Diseases of lambsquarters

These weeds are susceptible to a large number of plant diseases. The list of diseases commonly found on lambsquarter, and the crops they infect, include:

• beet curly top (beans, beets, celery, melons, peppers, spinach, squash, tomatoes
• mosaic viruses (alfalfa, bean, beet, barley, cucumber, eggplant, hops, lettuce, squash, watermelon)
• potato viruses X, M, and S (potatoes)
• ringspot virus (mulberry, tomato, pepper, potato, and stone fruits)

The green peach aphid, a serious disease-carrier, seems to prefer lambsquarters, which gives us yet another reason for pulling these weeds out as soon as they are seen.


Lambsquarters description

Lambsquarters start out with tiny dull bluish oblong leaves. You may see a reddish purple on the underside. As leaves mature, they take on more of a toothed, lance shape. Leaves are covered with a white, powdery coating, especially when new. Stems are sometimes tinged red or purple. Flower clusters form much like the seed heads of millet and quinoa.


Lambsquarters control

Pull them out. Dig them out. Don’t let them go to seed.

How hairy bittercress grows
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Found pretty much everywhere, hairy bittercress prefers moist soil, open ground, and freshly disturbed areas. Like other weeds, it grows rapidly, often having two generations each year. You may think they have disappeared during the heat of summer but the first autumn rain will let you know that they were merely waiting for wetter conditions. These plants have long taproots.

Hairy bittercress seeds are held in capsules, called siliquae. When the fruit within ripens, there are valves on the siliquae that create a tightly wound coil. That’s why, when you touch them, seeds  explode in every direction. This method of seed dispersal is called ballochory.


Problems with hairy bittercress

Once hairy bittercress takes hold on your property, you will be dealing with it more and more each year, for better or worse. Because of its ability to fling seeds near and far, and grow quickly, hairy bittercress often finds its way into your garden on nursery plants. It is far simpler to put new plants into quarantine and monitor for weed growth right along with pests and diseases.


Before you shrug off this seemingly minor weed, you need to know that the real problem with hairy bittercress is the fact that it can host some nasty diseases. Specifically, tomato spotted wilt and cucumber vein yellowing can be carried into your garden on hairy bittercress. These diseases can have a huge impact on several of your crops, and not just tomatoes and cucumbers.


It is far easier to monitor the ground each spring and autumn for tiny rosettes and then use your long weeding tool to get under the taproot before it takes hold.

Cutleaf geranium lifecycle

Cutleaf geranium can grow as either an annual or biennial plant, and is commonly found in disturbed ground and abandoned areas. Each plant can produce up to 150 seeds and those seeds can remain viable for 5 to 10 years.


Controlling cutleaf geranium

As with most the weeds, it is best to start controlling it early, before plants have a chance to go to seed. Hoeing is the best control.

​While grown as poultry feed and ground cover, common chickweed provides food and shelter for lygus bugs, thrips, pale-banded darts or spotted-sided cutworms (Agnorisma badinodis), and dusky cutworms (Agrotis venerabilis). Common chickweed can also carry cucumber mosaic virus and spotted tomato wilt virus.


​Succulent leaves grow opposite one another, and have a pointed tip. Common chickweed can reach 4 - 6” in height, but it generally grows as a short, dense mat, especially in lawns. The roots are fibrous and found near the surface. Stems tend to be weak, and plants produce white flowers and seed capsules at the same time. Common chickweeds plants have 5-petalled flowers, but each petal is split, to create the appearance of 10 petals.​​There are three species of chickweed found in California and they all germinate quickly and in abundance, under the cool, moist conditions common to California winters. Chickweed can complete its lifecycle in as little as 5 weeks, with each plant producing 800 seeds. If a single chickweed plant goes to seed in your garden or landscape, it can take 8 years before the seeds of that first plant are no longer viable. Be on the lookout for chickweed seedlings from January through the end of March. 


Common chickweed

Native to Europe, common chickweed (Stellaria media) is now found in many regions of North America and Asia. Also known as winterweed and chickenwort, common chickweed has been used as food and herbal remedy, though there is little or no scientific research to back up claims of common chickweed’s ability to provide cooling relief. Many people find the taste of this somewhat succulent annual too bitter to enjoy. Common chickweed contains high levels of iron, but the bitterness is caused by saponins, which can be toxic in large quantities.


Common chickweed is differentiated from its non-edible cousins by fine hairs found only along one side of the stem, whereas other, non-edible chickweeds have hairs all around the stem.

The good side of burclover

In addition to being grown as livestock and chicken food, California burclover is also used as a ground cover, winter erosion control, green manure, and in soil restoration. A drought tolerant legume that thrives on slightly alkaline soil, burclover requires very little water and it grows rapidly into a dense vegetative cover that adds nitrogen to the soil. A single acre of burclover can produce 8300 lbs. of biomass in a single season! In many areas of the world, burclover is rotated in pastures with cereal grains for a continuous supply of healthy food for livestock. If you were/are a farmer growing hay for livestock, adding burclover to your oats and wheat can increase production by 3 to 5 times.


But you probably see burclover as a weed in your lawn, as I do. Now that I know burclover is also a nutritious legume, I will feel better about feeding those weeds to my chickens.

​Annual sowthistle (Sonchus oleraceus) is also known as milk thistle, hare’s thistle, soft thistle, and hare’s colewort. As a member of the sunflower family, sowthistles have a taproot and they produce a milky white sap (latex).

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Annual sowthistle description

If you live in California, you’ve probably seen millions of these. Sowthistles can grow in only 1/2 an inch of soil, and they grow quickly. The cotyledons (seed leaves) are slightly football-shaped and less than 1/3 of an inch long. Early leaves are alternate, somewhat hairy, and feature margins (leaf edges) with backward facing teeth. Like dandelions, the stem is a smooth hollow tube. Mature leaves are a grayish blue-green. Upper leaves are smaller than lower leaves and there is no petiole (leaf stem). In many cases, the stem looks as though it is poking through the middle of the leaf, making them perfoliate. Lower leaves are deeply lobed and tapered. The flowers are yellow clusters that close at night (nyctinasty). These flowers matures into fluffy seed heads that blow in the wind, just like dandelions, but the seed heads are generally not a complete sphere.

Clover description

Clovers are also called trefoils because they nearly always have leaves in groups of three. [A four-leafed clover is said to be quatrefoiled.] Clovers are legumes, along with peas, beans, and alfalfa. This means they have a symbiotic relationship with certain Rhizobium bacteria that allows them to fix atmospheric nitrogen and use it to grow. For the most part, clover seeds start to germinate in the fall, and continue until temperatures rise above 60°F. Clovers are classified as annual, sweet, or perennial.

Beneficial clover
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Adding clover as a ground cover or a green manure can mean future plantings will thrive or, as the saying goes, “They will be as happy as a pig in clover.” Of course, bees love clover flowers, so be sure to plant your clover where you are less likely to step on a bee.


Clover controls

If clover is causing problems in your garden or landscape, the best control methods are hand-pulling, hoeing, and mulch. The mulch needs to be 4 to 6 inches deep to block clover. Clover seeds are very rugged, so composting and solarization are generally not effective controls.

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If you have bright green clover popping up in a yellow lawn, your soil is probably low on nitrogen.


Did you know that a group of clovers is called a cluff? I didn’t either.

Bermuda buttercup is a sunny yellow flower that appears in San Jose, California, each winter and spring.


Originally planted as an ornamental (oops), we now know that this South African invasive weed has the potential to make life quite difficult for our native species.​

Also known as sourgrass, Buttercup oxalis, Oxalis cernua, or simply oxalis, this low growing perennial is difficult to control. [The oxalis family is actually quite large and we will discuss that another day.] Close cousin to creeping woodsorrel, oxalis contains relatively high levels of oxalic acid, which is what gives it its sour taste. That is also why they should not be consumed in large quantities by livestock or your backyard chickens.


​Bermuda buttercup description

Three heart-shaped leaves that resemble clover make Bermuda buttercup (Oxalis pes-caprea) easy to identify. Most Bermuda buttercup plants have a loose rosette of basal leaves and tall stems, usually a foot tall, that feature bright yellow, 5-petalled flowers. You may see brown or purple spots on the leaves. Tiny bulblets form around the stem and more bulbs develop underground. Bermuda buttercup plants produce an average of 10 to 20 bulbs each year. Bermuda buttercup also spreads using runners and through contaminated soil.

Controlling Bermuda buttercup

This weed is very difficult to control, once it takes hold. Pulling the weeds does little to eliminate them, since the bulbs left behind are perfectly capable of starting the whole process over again. While Bermuda buttercup is rarely a problem in lawns, in can quickly become a serious problem in landscapes and home gardens. In the past 10 years, this invasive weed has choked out many native plants.


Homeowners are urged to eradicate this weed, to help prevent its spread into wildlands, where permanent damage may occur. Use the methods below to control Bermuda buttercup on your property, and please educate your neighbors, before it is too late.

• dig up plants as they are seen, taking care to remove all visible bulbs [repeat as needed]
• do not use contaminated soil elsewhere in the garden, without sifting it clean
• remove flower buds as soon as they are seen, to reduce bulb development
• soil solarization is the only effective removal method.

You will rarely hear me suggest herbicides, but this is one case where their proper use may be warranted. Always read the label and follow directions exactly. Seriously.

If you really must have pretty yellow flowers in your garden or landscape, please don't let it be Buttercup oxalis.

Few weeds come up as quickly and resiliently as common groundsel.


Also known as old-man-in-the-spring, this European annual weed prefers our cool, wet winter weather, dying off each summer, but it never fails to return each year. In fact, common groundsel is classified as a ruderal species, which means it is one of the first plants to start growing in disturbed soil.

Common groundsel description

Like other members of the sunflower family, common groundsel (Senecio vulgaris) features a sunny yellow flower. Akin to dandelion’s, mature seed heads transform into puffballs that fly on every breeze. The flowers of common groundsel are smaller than those of dandelions, and the green bracts have black tips. The plant has an upright growth, reaching up to 2 feet in height, but usually closer to 16 inches.


Rather than the lion’s tooth leaves seen on dandelion plants, common groundsel features pinnately lobed leaves (with matching loops and curves on either side), and may be toothed near the edges. Leaves are smaller near the top of the plant and may be covered with fine hairs. The leaves are sessile, which means they attach directly to the plant. The stems are hollow and the root system is a shallow taproot.


​Disease vector

If robbing nearby garden plants of sunlight and nutrients weren’t bad enough, common groundsel is also a carrier of disease pathogens (vector). It can host Cineraria leaf rust (Coleosporium tussilaginis), a fungal disease. It can also carry the fungus that causes black rot, another fungal disease that can affect citrus, chickpeas, cucurbits, such as cucumber or melon, tomatoes, and peas.


A toxic weed

While hailed as a medicinal plant, common groundsel contains chemicals, called pyrrolizidine alkaloids, that can make people and animals ill. Chronic exposure can cause irreparable liver damage. You’d have to eat an awful lot of it, but I avoid feeding it to my chickens, just to be on the safe side.


​Controlling common groundsel

Common groundsel is self-pollinating. Each plant can produce 1,700 seeds, and there can be  three generations per year. That ends up being a lot of weeds! The best way to control common groundsel is to prevent it from spreading in the first place. This means snatching seed heads any time they are seen and tossing them in the trash. Seedlings are far easier to pull than mature plants, so learn to recognize them and pull them out every time they are seen.


Heavy common groundsel infestations can be slowed or halted with sheet mulching. Follow these steps to successfully sheet mulch an area:

1. Remove and dispose of all seed heads.
2. Cut the plants off at ground level and leave them where they fall.
3. Water the area fully.
4. Cover the area completely with 3" to 4" of wood chips.

As with all weeds, this is an ongoing battle. Because these plants carry disease, it is better to be vigilant.


Good luck!

The word dandelion, which means lion’s tooth, actually refers to several different plants in the sunflower family. Native to Europe and Asia, dandelions have been following humanity across the globe, taking advantage of soil disturbed by agriculture, fires, and construction. This makes them a ruderal species. Ruderal species are the first plants to colonize disturbed land.


Bane of lawns everywhere, the common dandelion (Taraxacum officinale) was brought to North America in the 1600s to be used as both food and medicine. The species name officinale refers to an early English word meaning medicinal.

Dandelion plants
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Cousin to lettuce and chicory, dandelions are easy to recognize, with their low-growing (basal) rosette of toothed leaves and bright yellow or orange composite flowers. Composite flowers are actually made up of several florets, clustered together. Dandelion florets reflect ultraviolet light, which attracts many beneficial insects, looking for nectar and pollen. Surprisingly, dandelions do not need to be pollinated to set seed. Instead, seeds are produced asexually, in a process called apomixis. As a result, all offspring are identical to the parent plant. Besides the floral stem, dandelions are acaulescent, which means they appear to not have any structural stems.


​Dandelion flowers

Dandelion flowers open each morning and then close each night, in a behavior called nyctinasty. Each plant can produce up to ten floral stems. The cuplike structure seen at the base of each dandelion floret is called a calyculus. Once the flower has matured, it will begin to dry out. After the dried petals and stamens fall off, specialized leaves, called bracts, curve backwards, exposing the seed ball. Each stem produces a single seed ball. These seed balls are commonly called blowballs or clocks. The seeds we see are actually a special type of fruit, called a cypsela. The feathery bristles that act like a sail are called pappi (pappus, singular). The hollow flower stem contains a bitter latex used to defend against herbivores.

​Dandelion latex

Latex is used to make rubber. While most of the latex used to make rubber today comes from the rubber tree (Hevea brasiliensis), you can make your own rubber from dandelion latex! You can make an elastic band simply by coating your finger with dandelion latex, allowing it to dry, and then rolling the latex off your finger. Voilà! You can also make a bouncing ball or waterproof fabric out of dandelion latex. [Did you know that a man named Charles Macintosh figured out how to smear latex between two pieces of fabric to make waterproof fabric? That’s why raincoats are often called macintoshes!] When dandelion latex dries, it stays sticky until it cures. Curing latex involves applying heat and sulfur. The curing process removes the stickiness. Dandelion rubber is stiff in cold temperatures and supple when it is warm. Only Russian dandelions make a latex that is strong enough to be used commercially. [I just learned that one company is researching the use of Russian dandelion latex to make automobile tires!]


Dandelions as food

All parts of the dandelion plant are edible, but you may want to harvest the newest leaves to avoid some of the plant’s bitterness. Eaten the same way as spinach, dandelion greens are packed with good nutrition, including high levels of vitamins A, B, C, and D, according to the University of Maryland Medical Center. Dandelions also contain a lot of iron, calcium, potassium, and zinc. Young dandelion roots can be peeled and eaten. They are said to taste like turnips, but I haven’t tried them yet. The roots can also be roasted and used as a coffee substitute. The flowers are also edible. They can be sautéed in oil with a little garlic and they can be used to make dandelion wine.


Dandelions as medicine

Traditionally, dandelion has been used to treat infections, digestive problems, as a mild laxative, and to stimulate the appetite. Dandelion leaf tea was said to “purify the blood” and the milky latex was used as both mosquito repellent and wart remover, though I couldn’t find any scientific proof to back up any of these claims. According to WebMD, no research has demonstrated any verifiable medicinal use of dandelion, though it does contain chemicals that decrease swelling and increase urine production.


Dandelion roots

These herbaceous perennials have taproots that are strong enough to counteract compacted soil. Hell, they can break through concrete! While dandelion roots are typically only 6 to 18 inches deep, some specimens go 10 to 15 feet deep! Dandelion plants can live for up to 10 years and reach 20 inches in diameter.


I used to try to eliminate dandelions from my lawn, despite my love for their bright yellow flowers and the irresistible seed heads. I finally decided to try putting the plants to work for me in my heavy clay soil. While mulching and growing green manures and cover crops has significantly reduced soil compaction on my property, I have a theory about dandelion taproots. It goes something like this: Since dandelion taproots are strong enough to break asphalt, I allow them to grow, regularly removing the greens (for salads and as a treat for my chickens), before flowers emerge. My theory is that the dandelion taproots will dig down into my compacted soil, bringing microorganisms with them, to create healthier soil. Even if it doesn’t work, I still get pretty flowers and edible greens. Maybe I’ll even try making dandelion wine, one of these days. If my theory is wrong and I end up with a severe problem with dandelions and other, similarly growing weeds, I make have to resort to other control measures.


Dandelion control

If you really must get rid of the dandelions in your lawn, it will take consistent effort on your part. As you already know, those seeds can blow in on the wind from miles away. This battle never ends. While herbicides will certainly kill individual dandelions, those same chemicals can be toxic to other living things, such as us, and our pets. Maintaining a healthy lawn and removing plants as soon as they are seen is the best control method. Cutting off young plants at ground level, a practice called grubbing, is effective only if you are diligent. Crabgrass preemergent herbicides advertised as effective against dandelions do not prevent seeds from germinating.


Love ‘em or hate ‘em, dandelions have been around for 30 million years, and they are here to stay.


You may as well make the most out of these common weeds.

​Poison hemlock population explosion

Poison hemlock often grows alongside creeks and in locations with shade and moist soil. Many areas, including Cupertino’s McClellan Ranch Park and the Trukee River, see population booms after wet winters. Seeds (of many different plants) that had been dormant for several years use that moisture to germinate, rushing to reproduce. Just don't be fooled by this deadly plant's delicate appearance.


Just as the “leaves of three, let it be” rhyme has provided years of protection from poison ivy, try embedding this rhyme in your brain to help you stay away from poison hemlock:
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If you suspect poisoning from this plant, call Poison Control immediately at 1-800-222-1222. A quick response can save a life.

UPDATE:

Thanks to John, curator at the Carrot Museum,  I have learned that poison hemlock, for all its toxicity, is also used as a medicine. Seeds, roots, and leaves, when handled properly, can be used to treat respiratory conditions, such as whooping cough, asthma, and bronchitis. Poison hemlock has also been used to treat painful joints, to counteract anxiety and epilepsy, and to reverse strychnine poisoning.

Devil’s apple is a poisonous weed from Africa.


Called Devil’s apple because of its toxic yellow fruit, Solanum linnaeanum made an appearance under my almond tree. When I went to pull it out, I discovered its substantial thorns.

Considered an invasive in Australia, Devil’s apple has been getting a lot of press lately. Dramatic statements declare that Solanum linnaeanum can cure skin cancer. And I could not find a single piece of scientific evidence to back up those claims. Hmmm. Yet another snake oil salesman… Why do we tolerate all those untruths?


The truth about Devil’s apple is interesting enough on its own, so let’s learn what we can.


​Devil’s apple is a member of the nightshade family, along with potatoes, tomatoes, and eggplants. These shrubs can reach 6 feet in height, and those spines can be 1/2 an inch long. I sure wouldn’t want to fall into one of those bushes!


Also known as apple of Sodom, Afghan thistle, and Dead Sea apple, this weed invades pastures, agricultural fields, roadsides, and now, my yard.


The yellow berries start out as a star-shaped, 5-petaled purple flower, the way most nightshades do, but then they start looking more like a small apple, hence the name. The fruit changes from white or green to bright yellow and it contains toxic alkaloids. DO NOT EAT THEM!!!


Devil’s apple is also host to the Malaysian Fruit Fly, which earns it a listing in the California Code of Regulations, as part of the state’s emergency eradication program. Other than that reference, I have not been able to find any mention of the plant in California, so I have submitted an information request to local Master Gardeners and UC Davis to see if this is a new weed in the Bay Area. I’ll keep you posted.


For the time being, if you see one of these in your garden or landscape, dig it out.

Warm temperatures and moist soil are all it takes to help weeds invade your garden, lawn, and landscape. Fighting weeds is a constant battle, but it is much easier while they are young and vulnerable.

Why get rid of weeds?

Getting ride of weeds is work, so why bother? There are many reasons for getting rid of weeds:
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• weeds take up valuable real estate, nutrients, and water
• weeds can block sunlight
• weeds can carry plant diseases
• weeds can provide food and shelter for common plant pests
• weeds may release chemicals that slow the growth of nearby plants (allelopathy)
• climbing vines, such as bindweed, can choke out other plants
• some weeds, such as dodder, parasitize host plants
• some weeds, such as foxtail, can harm pets
• invasive weeds can push native plants, insects, birds, and animals to extinction

​So, getting rid of weeds helps your plants stay healthy. Most of the time. 


Benefits provided by weeds

Before trying to rip out every weed on your property, you may be surprised (and relieved) to learn, as I was, that some weeds actually provide benefits. Because they grow and go to seed so fast, weeds reduce erosion and the loss of top soil. Weeds can also be used to support soil microorganisms and to add organic material back into the soil. Weeds absorb carbon, keeping it out of the atmosphere, increase biodiversity, and provide food and shelter for native insects and animals. In some cases, weeds act as trap crops, luring pests away from favorite plants.


Looking at the sunny dandelion in this new light, we see it has a taproot that grows in even the most compacted soil, provides nectar and pollen for beneficial insects, new greens can be used in a salad, and flowers can be used to make wine! So, not all weeds are bad. But most of them are not what we want in our gardens.


What is a weed?

Before we start learning about some of the more common weeds, let’s be clear about what a weed is and what it isn’t. According to ​Gallagher, “If you pull it out and it grows back, it’s a weed.”  I’ve always said, "A weed is a plant that grows after you try to kill it.” So, how do we get rid of unwanted weeds?


​Weed control

​Weeds are some tenacious opponents. They have evolved to go to seed only days after emerging from the soil. Their stems and roots tend to be brittle, so part of them is left behind to continue after you try to pull them out. There are only two ways to get rid of weeds: the Hard Way and the Hard Way.

Which of these weeds cause problems in your garden?

Annual sowthistle (Sonchus oleraceus) Like dandelions, sowthistle seeds travel on the wind, so they will always be back. Learn to recognize these weeds while they are young, before they go to seed.

​Burning nettle (Urtica urens) and stinging nettle (U. dioica), have tiny hairs along the stem that sting for several minutes and can itch for hours. ​
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Common lambsquarters (Chenopodium album) may be edible, but these weeds can also carry beet curly top, potato viruses M, S, and X, tomato ringspot, and several mosaic diseases of alfalfa, barley, beans, beets, cucumber, eggplant, hops, lettuce, squash, and watermelons. ​​

​Field bindweed (Convolvulus arvensis) may have pretty flowers, but that root system can down 20 feet or more! Also, bindweed frequently plays host to viruses that impact beans, potatoes and cereals, such as tomato spotted wilt, vaccinium false bottom, and potato X disease. If you discover bindweed in the garden, your best bet is to monitor the area frequently and pull new growth as soon as it is seen. You can also use sheet mulching.

Pigweeds (Amaranthus spp.) provide overwintering sites for disease-ridden green peach aphids and beet armyworms, which negatively impact beans, buckwheat, celery, cilantro, citrus, cole crops, cucurbits, lettuces, parsley, peppers, strawberries, and tomatoes. ​​​

​Spotted spurge (Euphorbia maculata) is a common weed that can reach a surprisingly large size. Mature plants can be several feet in diameter!

​Of course, poison ivy, poison hemlock, and crabgrasses are commonly referred to as weeds, as are the many invasive plants being installed haphazardly. Kudzu, ice plant, purple nutsedge, and English ivy are wreaking havoc on local environments wherever they occur. Once established, it is very difficult to get rid of them.


If you are unsure about a potential weed in your garden, post pictures in the Comments section and we can work together to identify it.