Clovers

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.

White clover (Forest & Kim Starr) CC BY 3.0

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.

Little hop clover (Wikipedia) CC BY-SA 3.0

CA burclover (Ixitixel) CC BY-SA 3.0

Black medic (Tigerente) CC BY-SA 3.0

     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, also known as lesser trefoil or shamrock clover (Trifolium dubium) is frequently added to turfgrass mixtures.

Yellow sweetclover (AnRo0002)

    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.

Strawberry clover (Christian Fischer) CC BY-SA 3.0

Clover copycats

Clover is commonly mistaken for creeping woodsorrel and Bermuda buttercup, both members of the oxalis family (Oxalidaceae). Oxalis leaves, or false shamrocks, look very much like clover leaves, but they do not have a stipule. Stipules are small appendages, typically seen in pairs at the base of the leaf stalk.

Stipule (Pearson Scott Foresman) Public Domain

Beneficial clover
​
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.
​
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.