How can a clover be a weed? Is it all bad? Let’s find out!
California burclover (Medicago polymorpha) is an invasive annual weed that looks a lot like other clovers. The name polymorpha refers to the fact that the burrs can be smooth or snaggish. As far as weeds go, this one isn’t entirely bad. Also known as burr medic, bur trefoil, and creeping burr, this weed actually has a lot going for it.
Cousin to white clover, black medic, and strawberry clover, California burclover is sometimes grown on purpose to feed livestock. Being an annual, however, it will leave bare patches in your lawn, come summer. Also, those little burrs can wad themselves up on your favorite sweater and they are not particularly fun to step on barefooted. While some burrs are smooth, most of them feature rows of tiny velcro-like hooks that snag. Like other weeds, the best time to pull them out is when they are small and young, before they go to seed.
California burclover identification
Seed leaves (cotyledons) are oblong. The first set of true leaves are rounded. Mature burclover leaves look like they fold in the middle and are three round leaflets. They may have reddish midveins and toothed margins. Stems can reach 2 feet long and tend to trail, but may be upright, and they break easily. Small yellow flowers form in clusters at the end of stems. The seed pod is either smooth or a prickly burr that sticks to pet paws and fur, shoes, clothes, and enough other things that this pesky weed can easily be brought into your garden or landscape after a stroll around the block. These burrs look as though they are twisted on themselves. They start out green and then turn brown and hard. While these prickly burrs can get tangled in your pet’s fur, they are not the “stinging” “life threatening” weeds sensationalist articles claim. We will leave those claims to the foxtails.
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 is a common California weed that plays host to several garden pests.
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
Pests carried on sowthistle
Pests carried on sowthistle include lettuce aphids (Nasanovia ribis-nigri), lettuce root aphids (Pemphigus busarius), green peach aphids (Myzus persicae), and nematodes. Sowthistle should also be considered a vector of several different plant viruses. Pulling these weeds from your garden can break the disease triangle for many of these viruses, reducing or eliminating the need for more extensive treatments.
Pulling up seedlings as soon as they are seen is the easiest control. Unlike many other weeds, sowthistle does not regrow from root fragments. Since sowthistle only reproduces by seeds blown on the wind, preventing those seed heads from forming can significantly reduce your workload in the one run.
Luckily, sowthistles are easy to pull up.
Four-leaf clovers may bring good luck, but some clovers can be a real pain.
The word clover actually refers to three different genera of plants: Trifolium, Medicago, and Melilotus. There are over 300 species of clover and they are found throughout the Northern Hemisphere and occasionally in South America and Africa. Depending on who you ask, clovers can be beneficial ground covers or pesky weeds.
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.
Annual Clovers grow mostly in a prostrate manner from a single taproot. They feature tiny yellow flowers. CA burclover (Medicago polymorpha) and black medic (Medicago lupulina) are turfgrass weeds, while little hop clover, or shamrock clover (Trifolium dubnium) is frequently added to turfgrass mixtures.
Sweetclovers are upright annuals or biennials that grow from 2 to 5 feet tall. White sweet clover (Melilotus alba) and yellow sweetclover (Melilotus officinalis) often turn up in ornamental plantings.
Perennial clovers are often planted on purpose to reduce the need for nitrogen fertilizers. White clover (Trifolium repent) and strawberry clover (Trifolium fragiferum) both have the compound flower heads common to these clovers.
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.
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.
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 the Bay Area 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.
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.
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:
As with all weeds, this is an ongoing battle. Because these plants carry disease, it is better to be vigilant.
Sunny yellow flowers, toothed leaves, and a seed head that simply begs to be blown are all characteristic of the weed commonly known as dandelion.
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.
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 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.
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.
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.
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.
There’s the toe tappin’, git yer yee-haw on sort of bluegrass, and then there’s one of the most common California weeds: annual bluegrass.
Annual bluegrass (Poa annua) is a cool season annual or biennial that appears in the Bay Area with the first rains. This weed is a member of the grass family.
Annual bluegrass identification
Annual bluegrass starts out looking like many lawn grass varieties, Kentucky bluegrass, in particular, except that it has shallower roots, seeds more rapidly, and it is a lighter shade of green. To the untrained eye, grasses are grasses. A yellowish to dark green blade emerges, a couple more blades show up, and then a flowering stalk comes out of the center, hosting a flower cluster that spreads this problem far and wide. To identify annual bluegrass, you will need to take a closer look at the blade. The tip is said to look like the bow of a boat. The mid-blade may have a crinkly section. And the collar, where the blade meets the sheath (or stem), has a slightly pointed, jagged tip. Annual bluegrass grows low to the ground, spreading in clumps that can be 3 to 12 inches tall. The root system is fibrous and you may even see roots emerging from the lower portion of the aboveground stem. Flowers may be seen December through July. Flower heads are egg-shaped or triangular, and can be bright green or purplish.
Why do you care?
At first glance, this weed may look like an acceptable addition to your lawn. It’s a grass. It’s green. It grows like crazy. So, why would we consider this particular grass a weed? Well, first, it turns brown and dies back as soon as the top of the soil gets dry, leaving ugly, dead patches in your lawn. Those patches then erode or create homes for other weeds. In the garden, this weed robs your edibles of water and nutrients needed to stay healthy and produce an abundant harvest.
Annual bluegrass control
Watering your lawn deeply and infrequently will make life more difficult for annual bluegrass. It will also make your lawn healthier and more drought tolerant. Also, maintaining your lawn at a height of 3 or 4 inches will shade out this weed. Individual clumps can be dug out as soon as they are seen. I feed them to my chickens, but you can add them to the compost pile, as long as they haven’t gone to seed. Heavy infestations can be treated with pre-emergence herbicides in late summer or early fall, if you use that sort of thing. [I don’t.]
If annual bluegrass is seen in the garden, pull it out before it has a chance to go to seed and spread. You can also lay 6 to 8 sheets of wet newspaper over unplanted areas of the garden and then cover the paper with 2 to 3 inches of organic mulch, such as pine needles, straw, or aged compost. The wet newspaper acts like a weed barrier and the mulch feeds the soil while interfering with weed seed development.
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.
You can grow a surprising amount of food in your own yard. Ask me how!