Food storage and geophytes

Potatoes are tubers. Tubers are are type of geophyte. Geophytes are plant organs used to store food and water. They are also used in asexual reproduction. There are several types of geophytes: bulbs, corms, and everything else. That “everything else” is what we call tubers. Potatoes and yams are stem tubers. Stem tubers can emerge from modified stems. These stems can start out as stolons or rhizomes. Stolons are stems that grow at or just below the soil surface as “runners”. These “stems” are converted into adventitious roots at the nodes and what would have been a bud above ground becomes a spud below. Rhizomes are 'runners' that connect a parent plant to its offspring.

A modified stem

The “eyes” seen on a potato are actually stem nodes. Within each potato, you will find the same plant cells you would find above ground: vascular bundles, pith (spongy tissue), and cortex (outer tissue). Now here’s the funny part. While our standard spud grows from stem tubers, sweet potatoes grow from root tubers. The internal cell structure is very different. Root tubers have no nodes. That is why sweet potatoes have a more elongated form. At one end, you will find crown meristem tissue, which grows into stems and leaves. At the other end, called the distal end, the tuber produces roots. But enough of that, let's start growing some potatoes!

Commercial potato farming

Growing potatoes is surprisingly easy and I urge you to give it a try. In his book, The Botany of Desire, Michael Pollan describes how one potato farmer would not feed what they had grown commercially to their family, due to all the fungicides, herbicides and pesticides that are applied to commercial crops. That was a little misleading, since those chemicals are heavily regulated and rarely last long enough to be found on the food we eat. The real reason behind growing an untreated patch of potatoes was so they could enjoy the potatoes whenever they wanted them, rather than having to wait for the chemicals to dissipate. Personally, I don't use chemicals.

How to grow potatoes

While potatoes can can certainly be grown from spuds bought at the grocery store, this is a bad idea. Foods bought in the store are safe for human consumption, but they are not guaranteed to be free from common garden pests and diseases.  You are far better off buying certified “seed potatoes”.

The easiest way to grow potatoes is in a barrel, raised bed, or in a tower. If potatoes are planted in the ground, you will be finding rouge spuds for many years. Also, digging them up from the ground is, let’s face it, work. Growing potatoes in containers makes harvesting significantly easier and they make nice summer patio plants!

To begin, fill the bottom of the container(s) with 4" of loose, moistened soil. Cut seed potatoes into 2 inch chunks, making sure that each chuck has several eyes (small seed potatoes can be planted whole). Place the chunks 6" apart and cover them with 3" of moistened soil and repeat the process until the container is filled. Water lightly and be sure to place planters where they will get lots of sun. To build a tower (which works nicely for strawberries and herbs, too), simply take a section of chicken wire or hardware cloth and create a cylinder. Landscape cloth can also be used, but it may fall over. You can also grow potatoes indoors, near a window, if it gets enough light. Potatoes need loose, well-drained soil and frequent, light watering. Never let potato plants sit in water, they will rot. Potatoes use a lot of nitrogen and potassium, and they prefer acidic soil (as low as 4.8 pH).

At first, it will look as though nothing is happening. As a gardener, you know the value of patience. With time, water and sunlight, tubers will send out roots and stems that will pull nutrients from the soil and create carbohydrates out of sunshine. (Don’t you just love photosynthesis?) Before long, the container will be filled with lush, green growth. Aside from occasional watering and feeding (aged compost works great!), that’s all you have to do until it completes the season’s life cycle.

Harvesting potatoes

Eventually, the lush above ground growth will start to die off. When it starts looking ragged, dump the contents of the container out on a tarp and remove the mature potatoes. Now comes the really cool part: mix the remaining soil with some aged compost and do it all again with the immature spuds! I have been growing potatoes from the same batch of seed potatoes since 2011. To me, homegrown potatoes taste far better than store bought spuds.

Pests and diseases of potato

We’ve all heard about the Great Potato Famine. Over one million people died and another two million abandoned Ireland, all because of potato blight. Potato blight causes the tuber to rot in the ground. Other potato diseases include charcoal rot, corky ringspot, cucumber mosaic, curly top, fusarium wilt, leafroll, pink rot, sclerotium stem rot, cankers, verticillium wilt, and white mold. Many of these diseases can be prevented with good drainage and proper spacing between plants.

Common potato pests include aphids, beet leafhoppers, cutworms, flea beetles, potato psyllids, potato tuberworms, silverleaf whiteflies, Colorado potato beetles, Jerusalem crickets, and wireworms. But don’t let these threats stop you from creating your own potato patch.

Start your own potato patch today!

With a name like bottom rot, you know it won't end well.

Bottom rot is a fungal disease of lettuce and other leaf vegetables caused by the Rhizoctonia solani fungi. This is the same fungus that causes damping off. It lives in the soil and can be a big problem in warm, moist conditions.

Plants affected by bottom rot

In addition to lettuce, bottom rot can wipe out your Chinese cabbage, escarole, broccoli, radish, collards, Brussels sprouts, cauliflower, and turnip crops. The Rhizoctonia solani fungus also attacks potatoes, onions, beans, and corn.

Symptoms of bottom rot

At first, all you may see is some wilting of outer leaves. Closer inspection will show reddish-brown, sunken lesions on the midribs of leaves touching the soil. Brown or white fungal tissue may be visible, and lesions may discharge a light brown ooze. Leaf spots and brown lumpy bits may also be present on the plant. The fungus grows inward, toward the center of the head or body of the plant. The damaged plant tissue then becomes susceptible to other soft rots, causing a total collapse of the plant.

Controlling bottom rot

Fungicides are ineffective against bottom rot, so prevention is your only option. These tips will help protect your leafy bottoms:

• Clear out decomposing plant material before planting.
• Improve drainage and soil structure by adding organic material.
• Space plants for good airflow.
• Control nearby weeds which may host the pathogen.
• Irrigate at ground level and avoid overhead watering.
• Do not use more nitrogen than is needed.
• Use a 3-year crop rotation to break the disease triangle.

​
As with all bottoms, keep them dry, and they will be happy.

If you have never tasted a stevia leaf, you probably won’t believe the level of sweetness this herb provides. It just doesn’t seem possible. A single, delicate green leaf placed on the tongue does nothing. Start chewing and you’d swear you just downed a spoonful of sugar! Let’s find out if this is a plant you can add to your garden or foodscape.

Native to Paraguay and the surrounding tropical regions, stevia (Stevia rebaudiana) is also known as sweetleaf. Stevia is the model used to create several ‘natural' sweeteners, except that most of them are not what we gardeners would think of as natural.

​The majority of these stevia plants are grown in China and the leaves are so highly processed that there is little left besides the sweetness. [Being 200 times sweeter than sugar, stevia packs a powerful sweetness punch, processed or not.] Using the unprocessed leaves as a sweetener, on the other hand, adds several different compounds, called glycosides, plus antioxidants, and we all need those!

​The stevia plant

​Being a tropical member of the sunflower family, stevia loves the heat. This tender perennial prefers USDA Zones 9 - 11, and is grown as an annual elsewhere. Stevia grows best under the same conditions as basil.  Like basil, stevia needs some protection from the high heat of our California summer. Plants can reach 1 to 4 feet high and wide, depending on temperatures and the local microclimate.

How to grow stevia

Stevia plants can be grown from seed, but results are hit-and-miss, as germination is tricky. If you decide to try your hand at seed starting stevia, begin indoors, 8 to 10 weeks before your last frost date. Seeds germinate best at temperatures between 68 and 75°F. Fill pots with a light potting soil or peat mixture. Press seeds into the soil and cover with perlite. This will protect seeds from the air and help the soil retain moisture, but provide seeds with the light they need to germinate. To avoid flooding seeds into the corners, water by misting heavily, at first.

Like peppers, stevia plants benefit from the use of a waterproof germination mat. This gives them the heat they need to get started. Cover the pots with plastic and check twice a day to ensure that the top 1/2-inch of soil remains moist until germination occurs, which should take 10 to 15 days.

Stevia needs well-drained soil. This makes them an excellent choice for large containers or raised beds, where high quality potting soil provides plenty of macropores and micropores in the soil. During summer heat, these plants need almost daily watering. Allow the soil to almost go dry before watering again.

If you allow your stevia plants to go to seed, you can collect seed heads or let them grow where they fall. If you collect the seeds, discard light-colored specimens, as they are probably not viable. Most often, new plants are started from rooted cuttings.

Stevia pests and diseases

Outside of greenhouses, cutworms and sugar addicts are stevia’s only serious threats. In close quarters, aphids, whiteflies, and thrips can can become a problem.

Harvesting stevia

You can use stevia leaves fresh from the plant or you can harvest and dry them for later use. The sweetness remains unchanged in either case. Leaves are at their sweetest just before flowering. Once the plant flowers, leaves do not taste as good or as sweet. Each plant can provide you with approximately 1/2 pound of dried leaves each year.

Using stevia

Stevia is used to sweeten teas and other beverages, fruits, yogurt, custards, salad dressings, and many other liquid-based foods. Stevia can be used to replace some, but not all, of the sugar in baked goods. [Sugar has certain chemical properties that are needed in baking that stevia cannot provide.]

Before adding even more sugar to your diet, how about adding stevia to the garden, instead?

Earworms. Those songs that get caught in our mind and play over and over and over… These are not those earworms, but they can be just as annoying.

You don’t grow corn, you say? Don’t think that your garden plants are off the hook, just yet. The larval form of the corn earworm (Helicoverpa zea) goes by several names, such as cotton bollworm and tomato fruitworm. Tomato?!!? Yes, this is the dreaded tomato fruitworm. And these innocuous-looking moths can migrate as far as 400 km (or nearly 250 miles) to get at many favorite garden plants, including melon, beans, spinach, soybeans, peas, okra, squash, and sweet potato.

​Heat-loving plants, such as tomatoes, peppers, basil, and eggplant, get a much better start when protected with a cloche early in their development. Seeds or seedlings can be placed under a cloche after the soil has been watered. Most of the moisture will stay trapped in the cloche, but occasional waterings will still be needed as the plant grows. Because a glass cloche holds heat and air within, it can get too hot and too humid for your young plant.

​Occasional venting is necessary. To do this, simply slide a piece of wood or a rock under one edge of the cloche to increase air flow. In the evening, before temperatures start to drop, remove the prop and allow the cloche to sit flat on the ground again. If your cloche is made with fabric, venting is not needed. Once the plant outgrows the cloche, simply store it for another season or use it on another, smaller plant.

Cloches can also be used to help sensitive perennials make it through winter.

Junebug damage

Adult Junebugs feed on leaves. They fly in from weedy areas to feed at night. During the day, they tend to hunker down in a shady spot or burrow into the soil until dusk. The damage they cause is similar to Fuller rose beetles, earwigs, and snails. Grasshoppers and caterpillars may also cause similar damage. The only way to be sure is to catch them in the act.

The more insidious damage occurs underground as Junebug grubs feed on the roots of your lawn, especially ryegrass and bluegrass. Symptoms of infestation include brown, dying patches. If things get really bad, you can actually roll up patches of turf because it is no longer attached to the ground! Large numbers of Junebugs can defoliate a young tree in a matter of days. This is especially true for avocado trees, which may need to be protected with netting.

Controlling Junebugs

Commercial growers use blacklight traps when Junebug infestations cause too much damage. This is not recommended for home growers because the trap may attract more Junebugs than it captures. Heavy infestations are treated with an application of entomopathogenic nematodes. For the most part, home gardeners can’t do anything besides hand pick them whenever they are seen. Junebugs really are clumsy flyers, so it’s not hard to catch them. They are attracted to lights at night and often bump into windows and screens. When I catch them, I feed them to my chickens, who are very happy to help with Junebug control.

If you have children, you can always gift them a butterfly net and offer a bounty on every Junebug they catch!

“Six years you shall sow your land and gather in its produce, but the seventh year you shall let it rest and lie fallow, that the poor of your people may eat; and what they leave, the beasts of the field may eat. In like manner you shall do with your vineyard and your olive grove.” Exodus 23:11

Growing toward sunlight

Instead of passively shrinking to one side as the sun’s harsh rays boil away a plant’s bodily fluids, we now know that plants actively grow toward (or away from) sunlight. [When a plant grows away from sunlight, it is called skototropism.]

Experiments conducted in the 1800’s demonstrated that plants will respond to any type of light: street lights, grow lights, or sunlight. When plants are attracted to this light, it is called phototropism. Phototropism is a function of the hypocotyl, or individual cells found in the same region. Hypocotyls are the embryonic stem found below the seed leaves (cotyledons) and directly above the root. You can easily see examples of phototropism when seedlings first emerge and they don’t get enough sunlight - they become leggy and lean toward whatever light they can. This is phototropism.

In heliotropism, not any old light source will do. It is only radiation from the sun that causes the reaction. And the mechanical causes of these two types of movements are very different.

Mechanics of plant movements

When plants move in response to the position of an external stimulus, it is called a tropic [TRO-pic] movement. If a plant’s movement is independent of the stimuli’s position, it is called a nastic movement. In phototropism, plant hormones (auxins), found in the meristem tissue of leaf and stem tips, photoreceptors, and multiple signaling pathways are used to direct a plant to grow more rapidly toward sunlight. In heliotropism, a structure called the pulvinus is used to direct movement.

The power of pulvinus

The pulvinus is an amazing, fluid-controlled joint found at the base of a plant leaf stem (petiole) or just below a flower.

The pulvinus causes movement by altering fluid pressure in the surrounding plant tissue. These changes in fluid pressure start when sucrose is moved from the phloem into the apoplast. The apoplast is the conjoined spaces between plant cells. As sugar is pumped into the apoplast, potassium ions are pushed out, followed by water molecules. This changes the pressure within the affected cells, causing movement. This is called turgor-mediated heliotropism. But not all heliotropic flowers have a pulvinus. Those that do not are still able to move by permanently expanding individual cells. This is called growth-mediated heliotropism. Pulvini are also used in response to nyctinastic and thigmonastic movements.

Heliotropic flowers

Heliotropic flowers face the sun from dawn to dusk. Slowly tracking the sun’s path across the sky, these flowers are believed to use heliotropism as a way to improve pollination, fertilization, and seed development. Heliotropic flowers often have five times as many beneficial insects present, due to the added warmth. [Many tropical flowers exhibit a modified form of heliotropism in which flowers maintain an indirect tracking of the the sun. This is believed to reduce the chance of potential overheating.] Beans, alfalfa, sunflowers, and many other species turn their blooms to follow the sun’s path across the sky each day. But sunflowers only use heliotropism in their early development, in the bud stage. Once a sunflower head emerges, it may track the sun for a short time, as an expression of phototropism, until the flower head reaches full size. The majority of sunflowers found in the northern hemisphere nearly always end up facing east.

Leaf heliotropism

Like floral heliotropism, leaf heliotropism is the method by which plants focus their leaves perpendicularly to the sun’s morning rays (diaheliotropism), or parallel to midday sun (paraheliotropism). Diaheliotropism allows leaves to capture the maximum amount of energy from the sun, while paraheliotropism protects plants from overheating and dehydrating.

How do your plants move during the day?

Periderm

The periderm is also made up of three layers: the cork, cork cambium, and phelloderm. Cork (phellem) is produced by a specialized layer of cambium tissue, known as the cork cambium, or phellogen. This cork cambium layer is only one cell thick and the cells divide in parallel (or periclinally) toward the outside of the tree. In some trees, the cork cambium layer also produces cells towards the inside of the tree. These inner cells are the phelloderm layer.

Function of cork

Cork keeps wine safe from the elements because it is impermeable to gases and water. Because of the cork, your wine stays where it is and (as long as the cork remains intact) will only grow better with time. The cork of a tree also blocks air and water. Cork is able to keep trees and wine safe from the elements, along with insects, bacteria, and fungal disease because it contains suberin. Surberin is a waxy material that creates a protective barrier. This barrier also blocks water and gas exchanges between the outermost layers of the tree killing the epidermis, cortex, and secondary phloem. This is the bark you see.

Trees and shrubs also use cork to cut off an unwanted body part (leaf, diseased twigs, mature fruit) from the rest of the plant. This is called abscission.

Berries vs. soroses

While mulberries may appear to have the same structure as blackberries and raspberries, botanically, they are quite different. Raspberries and other members of Rubus are made up of several drupes (a type of fruit) that are clustered around and attached to a dry thalamus. All of the drupes in a single fruit are made from a single flower. In mulberries, and other soroses, each rounded bit is its own fruit, formed from its own flower.

​Some garden words are fun to say. Schizocarp [ˈskitsōˌkärp] certainly qualifies.

A schizocarp is a type of dry fruit that splits into single-seeded parts, called mericarps, when ripe. Each mericarp is made from its own carpel. [A carpel is the female reproductive parts of a flower, including an ovary, stigma, and usually a style.] Mericarps can be dehiscent, which means they split open when ripe, or indehiscent, which means they stay closed.

The science of clay

Clay is just one type of soil. Soil is made up of varying combinations of sand, silt, clay, air, water, minerals, microbes, earthworms, and more. All those ingredients are arranged into soil structures called aggregates, which contain solids and spaces. [This is different from soil texture, which refers to the percentage of sand, silt, and clay found in a sample.] The particles of various minerals found in soil are measured in micrometers (μm), or microns [one micron equals one-millionth of a meter]:

• sand - unreactive quartz, shells, obsidian and other minerals; larger than 50 μm
• silt - boxy or spherical particles of quartz or feldspar; 2 to 50 μm
• clay - flat plates of feldspar that hold together using electrostatic forces; less than 2 μm

The spaces between soil particles are called macropores and micropores. Macropores are greater than 0.08 mm and they hold air and water. Because the spaces are larger, water moves passively, pulled by gravity. Micropores are less than 0.08 mm and mostly hold air. Macropores are so small that the surface tension of water molecules means active suction must be used to pull the water out of these tiny spaces. Clay soil has far more micropores than macropores, so water and nutrients are held tightly, which means it is less porous.

Porosity, or permeability, refers to the ability of air and water to move through soil. Soil that is rich in organic material tends to have better porosity. Porous soil allows roots to find water and nutrients, and allows for healthy gas exchanges. Being flat, clay particles lie on top of each other like a deck of cards. This is why clay soil is so susceptible to compaction.

Clay and soil compaction

Compacted soil can create a barrier to roots seeking water, nutrients, and stability. It can even alter nitrogen, making it unavailable to plants (denitrification). This is especially true next to streets, driveways, buildings, and other heat islands. [If your unimproved clay soil ever feels spongey, it may indicate a masked chafer infestation.] On the other hand, leaching of nutrients is far less common in clay soil. More often, we end up with a super abundance of certain nutrients that creates an imbalance for our plants.

Clay soil and plant nutrients

Clay is made up of many negatively charged secondary minerals. That negative charge loves to attract and hold on to cations, or positively charged particles, such as potassium, zinc, and nitrogen. [That’s why most San Jose soils have an abundance of potassium.] This attract-ability gives clay soil a high cation exchange capacity (CEC), which is a fancy ways of saying clay can hold onto 6 to 8 times more water and nutrients than sand. If you get a soil test (and I urge you to do so), you will also see a base saturation figure. To illustrate, CEC can be seen as the number of electrical outlets in your home, while base saturation is the number of those outlets currently being used. On average, sand has a CEC of 5-15, silt has a CEC of 8-30, and clay has a CEC of 25-50.

In the same volume of soil, clay has 100,000 times more surface area than sand, so there are plenty of places for attachments to occur. You can improve your clay soil’s base saturation by monitoring and correcting soil pH. Alkaline soils may need acidification, while acidic soils may need the addition of lime to bring the pH into a range suitable for plant growth (6.0 to 7.0). A proper pH can make important nutrients, such as iron, available to your plants.

Safety note: When planting trees around your home, keep in mind that root systems of plants growing in clay tend to be smaller, because so many more nutrients are available closer to the tree. This can result in a smaller in-ground support system for your tree, which makes it more likely to fall. Just sayin’…

Clay and drainage

When soil is extremely dry, it can’t absorb water because it becomes hydrophobic. Like a dry sponge, the water simply rolls off. Clay soil can act the same way. The rate at which water can enter soil is called its infiltration rate. Infiltration rates are given as millimeters of water absorbed per hour:

• sand - 30 mm/hr
• loam - 10 to 20 mm/hr
• clay - 1 to 5 mm/hr

It is normal and healthy for the pruned tip of a twig to dry up and seal itself off from pests and disease. When that death keeps moving inward, there’s a problem. This creeping death is called dieback. Dieback can be from environmental conditions, insect feeding, or disease.

Viral dieback

Lettuce is susceptible to viral dieback caused by the lettuce necrotic stunt virus. This pathogen causes stunting, leathery, dark inner leaves, and rotted areas on outer leaves.

Bacterial dieback

Apple, citrus, pear, and stone fruits are susceptible to bacterial blast, blight, and cankers, all caused by Pseudomonas syringae. This pathogen kills flower clusters and nearby leaves, along with twig tips. Fireblight is another bacterial infection that causes twig dieback. This disease is easy to spot because the dead twigs curl into a shepherd’s crook shape. Watch for fireblight in June. Huanglongbing, a deadly citrus disease, includes twig dieback as one of its early symptoms.

Too much water can result in a lack of vigor or sudden death by Phytophthora root and crown rot. Phytophthora is Greek phytón (plant) and phthorá (destruction), so the name means the plant-destroyer.

What is Phytophthora root and crown rot?

Phytophthora [Fie-TOF-ther-uh] is a family of water molds called oomycetes. Oomycetes fall somewhere between fungi and algae in the web of life. There are many different types of Phytophthora molds. They generally attack stems and roots. Stem damage occurs at or just above the crown, at the soil line, though it can appear elsewhere on a plant. These molds cause many plant diseases, including sudden oak death, potato blight, damping-off disease, and crown rot. Phytophthora root and crown rot can kill a tree or shrub if the soil remains wet for too long or when planted too deeply. [Moist soil around the trunk is never a good idea.]

Host plants

Nearly all fruit and nut trees, including cherries and kiwifruit, are susceptible to Phytophthora root and crown rot. But so are members of the nightshade and cabbage families. So, tomatoes, eggplant, and potatoes are vulnerable, as are cauliflower, Brussels sprouts, and cabbage. And all because of too much water.

Symptoms of Phytophthora root and crown rot

Plants affected by Phytophthora root and crown rot look drought stressed. Unfortunately, because the natural response is to provide more water - the last thing you want to do when Phytophthora is present. Symptoms start in just one branch or area of the affected plant before spreading. Leaves may turn purple or reddish. Plants may die suddenly or linger poorly for years before dying.

Symptoms can vary greatly, depending on the type and age of the plant, the plant’s genetic resistance to infection, overall health, soil temperatures, and moisture levels. The bark around the crown and upper roots of infected plants is dark. A dark sap or gum may ooze from damaged areas. Using a sharp knife, cut away an area of bark. Infected plants will show reddish-brown streaks or patches. Water-soaked areas on roots may also be visible. If white threads are visible between the bark and the inner layer or around the root system, it is Armillaria root rot.

​Preventing Phytophthora root and crown rot infestation

Proper water management is the best way to prevent and control Phytophthora root and crown rot. Never allow standing water to remain around tree and shrub trunks. Also, don’t let sprinklers hit tree trunks. These other tips can help you manage Phytophthora in your garden or landscape:

• Only use certified pest- and disease-free plants.
• Install plants at the proper depth.
• Avoid over-watering.
• Allow soil to dry out between waterings.
• Ensure proper  drainage.
• Quarantine all new plants for 4 to 6 weeks, including water that may drip from the containers.
• Sanitize tools, boots, and hands after handling potentially infected plants.
• Sanitize shoes with bathroom cleaner after walking through an infected area
• Do not add infected plants to the compost pile.
• Employ crop rotation to interrupt the disease triangle.

You may be able to maintain an infected plant with proper irrigation and good cultural practices, but it will never be the same. Phytophthora can stay in the soil for many years, so prevention is far easier than control.

NOTE: One new-to-us variety, Phytophthora tentaculata, is on the Dept. of Agriculture’s watch list. If it appears in your garden or landscape, contact your local Cooperative Extension Office. They may have helpful advice to protect your plants and need to know where this disease is spreading. 

The ginger plant

Ginger was one of the first spices to be exported from the Orient and it is a fascinating plant. As a plant family in its own right, ginger (Zingiber officinale) is cousin to turmeric and cardamom.

The ginger we eat is not actually a root. It is a rhizome. Rhizomes are modified, underground stems that put out lateral shoots and adventitious roots. Ginger plants do not have aboveground stems. Instead, they grow much like the grass in your lawn, with leaves rolled together at the base of the plant to form pseudostems, except that they can grow to three or four feet tall! Equally tall floral stems emerge directly from the rhizome. Flower buds start out green and then turn white and pink before opening up into mature flowers. Mature flowers can be pale yellow, deep purple, or brilliant red, depending on the variety.

Harvesting ginger

While you can harvest ginger rhizomes at any time, it is best for the plant’s long term health if you wait until the aboveground portion withers, similarly to garlic. The desired portion of the rhizome is cut off and the rest of the plant can be returned to its container. The cut off portion is then scalded to prevent it from sprouting. The older ginger gets, the tougher and drier the rhizome becomes. Ginger is a perennial plant, which means it keeps on growing. It may look as though it dies in winter, but don’t be fooled. Unless your region is too cold for ginger, it will come back year after year. Each little nub on a ginger rhizome is a potential new plant.

Seeing unripe fruit or nuts on the ground, under your tree, can be normal or may indicate a problem.

Fruit drop, or June drop, is a natural process that allows a tree to get rid of more fruit than it can support. Fruit drop is common to citrus, apple, avocado, almond, tomatoes, and many other crops. Earlier in the growing season, some trees will rid themselves of unwanted blooms (blossom drop) for the same reason. Some trees, such as loquat, can be messy during this time. Manual fruit thinning works the same way, reducing the quantity of fruit but improving its quality.

Magnesium levels

​Too much magnesium in the soil makes it difficult for plants to absorb calcium and other anion nutrients, which can lead to blossom end rot, bronzing, and many other problems. This is a common problem in areas with alkaline soil. The opposite is true in areas with acidic soil. Insufficient magnesium symptoms look very much like potassium toxicity symptoms: older leaves, at the bottom of the plant, start turning brown, between and alongside the leaf veins, working upward through the plant. Magnesium deficiencies in stone fruits often start out as slightly brown areas along leaf edges (margins) that expand inward, causing cracking, necrosis, and leaf loss. Magnesium deficiency in California is extremely rare.

Stabilizing magnesium levels

Reaching and maintaining ideal mineral levels in soil for healthy plant growth is both science and art - mostly science. To start, get a soil test from a local, reputable lab. Unfortunately, over-the-counter soil tests are not yet accurate enough to be useful. Once you have your results, you can take these other factors into consideration:

• Local water supply Irrigation water that is more alkaline, such as we have in San Jose, California, tends to make calcium and magnesium less soluble, and harder for plants to absorb. This is because of carbonate and bicarbonate ions in the soil. The chemical transformation between these molecules also tends to leave salts behind.
• Soil pH Acidifying alkaline soil with ammonium sulfate or sulfur can help reduce the number of ions (Residual Sodium Carbonates) that make magnesium more available to your plants. If you have acidic soil, wood ashes can be a good source of magnesium and other plant nutrients.
• Soil structure Compacted soil makes it difficult for plant roots to access nutrients. Overly loose (sandy) soil cannot hold nutrients long enough for roots to find them. Incorporating organic matter as a top dressing will improve soil structure and soil health, leading to healthier plants.
• Compost Applying compost, mulch, and green manure are good ways to add magnesium and other plant nutrients to your soil.

Finally, schedule regular soil tests for your garden and landscape. Look at these tests as an annual physical for the living skin of your property. The information in these tests will help you make informed decisions about the magnesium in your soil.

If older leaves on cucumber, melon, or squash turn yellow and leathery, they may have cucurbit aphid-borne yellows.

The cucurbit aphid-borne yellows luteovirus (CABYV) causes this viral disease. Luteoviruses are a genus of viruses that use plants as hosts. Aphids carry this disease and spread it to plants as they feed.

Symptoms of aphid-borne yellow virus

Early symptoms are chlorotic (yellow) areas on lower leaves. These spots expand to include the entire leaf, leaving the large veins bright green. The affected areas become leathery and brittle. Stunting and fruit drop are common symptoms as the plant struggles. Before genetic testing, gardeners thought this was plant aging (senescence), nutrient deficiencies, or other diseases, like cucurbit yellow stunting disorder.

How the disease spreads

As the name suggests, aphids carry this disease. As aphids pierce plant tissue to feed on sap in the xylem, they spread infection. Once infected, the aphid will continue to spread the disease as it feeds on squash family plants. Lettuces, beets, and many weeds can also become infected.

Controlling aphid-borne yellows

There is no way to control the virus, but you can reduce the presence of aphids in your garden with these tips:

• Install silver reflective mulch at planting time to repel aphids (remove it as temperatures rise).
• Install row covers to exclude aphids.
• Fertilize and irrigate plants properly to keep them healthy.
• Avoid using broad-spectrum pesticides, which kill off beneficial predators that eat aphids.
• Clear aphid-bearing weeds from the immediate area.

Remove and destroy infected plants to prevent the disease from spreading to nearby plants

Fresh, sweet cherries are delicious, but cherry trees can be difficult to grow.

According to UC California Backyard Orchard, “cherries are the most difficult trees to keep alive.” If you are still determined, let’s see what we can learn about these trees.

People have been enjoying cherries since prehistoric times. Cherries are stone fruits, which means the fruit is a drupe. There are two types of cherry trees: sweet (Prunus avium) and sour (Prunus cerasus). The two cannot cross-pollinate with each other. Both types are native to Europe and western Asia. Sweet cherries are also known as wild cherries or gean.