Trifolium pratense L.
Trifolium pratense L. var. frigidum auct. non Gaudin
Trifolium pratense L. var. sativum (Mill.) Schreb.
Red clover is native to Europe, western Asia, and northwest Africa. It was brought to North America (and many other places), and it is now abundant. Red clover is grown extensively for pasture animals.
Here is a comparison among red, white, alsike, and crimson clovers:
|Plant||Plant stems are 4-16" (10-40 cm) long, but often lying on their sides, so these clovers are usually close to the ground||12-24" (30-60 cm) tall, typically somewhat smaller than red clover and larger than white clover. It has multiple hairless, fairly flexible stems||20" (50 cm) high.|
|Flowers||On flower stalks 1-4" (2.5-10 cm) long. Flowerheads are ½-1¼" (1.3-3.2 cm) around, rounded, white, sometimes pinkish||½-¾" (1.3-1.9 cm) around, and may be pink on the bottom, grading to white on the top; or pink throughout. The shade of pink is lighter than with red clover||Deep red, forming rounded conical flowerheads about 1" (2.5 cm) tall and ⅝" (1.7 cm) around. Flowering occurs during April to May.|
|Leaves||Leaves are round or oval, in groups of three, each roughly at right angles to the others.|
|Habitats||Waste ground, pastures, open fields, roadsides, railroads||Moist meadows near woodlands, pastures, abandoned fields, and roadsides|
|Occurrence||Very common||Common, but less so than red and white clovers|
Identification: Plants are 8-31" (20-80 cm) tall, multiply branched, often partially lying down. Stems are sometimes purplish and sometimes hairy. Leaves are in 3-leaf clusters. Leaflets ⅜-2½" (1-7 cm) long × ⅜-1½" (1-4 cm), with a distinctive pale green crescent or “V” on the outer half of the leaf. They vary from roundish to an elongated oval. Flowers are pink to rose (rarely white). Flowerheads are about ¾" (1.9 cm) around.
Medical: As is typically the case with very common plants, various healing properties have been attributed to red clover. One of the more widely believed properties is that clover contains substances that can treat post-menopausal symptoms. A controlled study by the George Washington University School of Medicine, published in the journal Menopause, found that clover has no such effect.
But as a fertilizer...
Rolling your own fertilizer
Nitrogen is one of the essential building blocks of all life. There is no shortage of nitrogen—it makes up almost four fifths of our atmosphere—but neither plants nor animals can use it directly in its atmospheric form (N₂). It takes energy to convert it to a usable form, for instance, to ammonia or nitrates. Energy from lightning, for example; or energy from the vast amounts of electricity used to create commercial nitrate fertilizers. If a plant could somehow harvest nitrogen directly from the air, it would be able to make its own fertilizer, allowing it to colonize soils that were too poor in nutrients for other plants.
Legumes, including alfalfa, clover, peas, beans, lentils, soybeans, and peanuts, have managed exactly this stunt, called “nitrogen fixing”—and without even solving the problem themselves. Instead, they brokered an amazing agreement with the real inventors of nitrogen fixing: symbiotic bacteria known as Rhizobia. The bacteria grow in nodules on the roots of legumes, supplying the plant with usable nitrogen in return for malates and succinates for energy and carbon. The bacteria combine nitrogen, hydrogen, and electrons like this:
N₂ + 8H+ + 8e– → 2NH₃ + H₂
We could write this more simply as:
nitrogen + hydrogen + electricity → ammonia + hydrogen
The eight hydrogen ions (8H+) in this reaction come mostly from water vapor. The electrons (8e–) can be thought of as electricity created by the bacteria. The results of the reaction include ammonia (NH₃) and hydrogen (H₂).
The created hydrogen reacts pretty quickly with oxygen, forming more water vapor. And the ammonia is very close to what the plant needs. In water, ammonia quickly reacts with hydrogen ions in the water to create ammonium ions:
NH₃ + H+ → NH₄+
ammonia + hydrogen ions → ammonium ions
You are already familiar with this reaction—it is the same one that makes you wrinkle your nose in disgust when you catch a whiff of ammonia. But what smells bad to you is a critical nutrient to most plants.
The ammonium ions created by the bacteria are absorbed directly by the roots of the legumes. The trapped nitrogen feeds the plant, with enough left over after the plant dies to foster the growth of other plants as well. Thus legumes are sometimes called green manure.
So before you get too irritated with the clover growing in your lawn, consider that it is busy fertilizing your lawn.
Trifolium pratense at the Oregon Flora Image Project
Trifolium pratense on Missouriplants.com
Trifolium pratense in Paghat's Garden
Trifolium pratense on Wikipedia
Trifolium pratense on Plants for a Future, a resource and information centre for edible and otherwise useful plants
Trifolium pratense on hort.purdue.edu
Trifolium pratense on the Virginia Tech Weed Identification Guide
Trifolium pratense description by Thomas H. Kent, last updated 25 May 2020.