Dan Hemenway
Clover
Whether three- or four-leaved, you’re lucky if your lawn contains clover. Like dandelions, ‘White Dutch’ clover, the kind commonly found in lawns, rates high for sequestering fertility chemicals in Kourik’s table of dynamic accumulators.
Clover supports bacteria in its roots that take nitrogen out of the air in the soil. If the soil is compacted, there is little or no room for air, so the bacteria have nothing to work with. I’ve dug alfalfa in tractor-compacted soil, and even though the seed had been inoculated with the right bacterial species, there were no tell-tail nodules (tiny bumps) on the roots. Clover and grasses combined can make soil more friable (a structure beneficial to soil life, including nitrogen-fixing bacteria and fungi that are so beneficial to plants that they almost seem to cultivate them). That accounts for the benefit of having all three plant types — dandelion, clover, and grasses — in your lawn. Fortunately, this tends to happen naturally, although it may be helpful to broadcast clover if it is absent, being sure to buy inoculant from the farm or garden store and apply it to the seeds according to directions. (Vegetable-garden legume inoculant will not fix nitrogen on clover. You have to buy the right type.)
Clover roots descending from the site where its seed germinated are taproots, a bit more divided and not quite as effective as dandelion as an organic crowbar. ‘White Dutch’ clover also has stems that spread along the surface, making branches as they go. In my observation, these lateral stems do not form a taproot. Instead they form a network, contributing to soil friability, although less so than grasses. Among these fine roots, nitrogen-fixing bacteria, if they are present in the soil, convert inert atmospheric nitrogen to fertilizer. Some of the fixed nitrogen leaks from clover roots, stimulating the grasses and dandelions.
Unlike most other plant groups, growth of legumes, such as clover, is not limited by available soil nitrogen. Instead, clover growth is limited by the amount of available phosphorus. According to Kourik’s table, ‘White Dutch’ clover is particularly good at extracting phosphorus from soil. Safe, economical, and environmentally appropriate sources of phosphorus fertilizer are hard to find. Often, soil “ties up” phosphorus in a chemical form that most plants can’t use. Phosphorus accumulators can take up some of the tied-up phosphorus. Unlike nitrogen fixed in the atmosphere, which is about 70% nitrogen, clover can’t make phosphorus out of thin air.
Like dandelions, clover blossoms also provide food for the adult insects whose babies will munch some of your garden pests.
Clover leaves are edible. Raw they taste like many edible leaves, at least to me.
Grasses
The grass-clover relationship is dynamic. It has been the basis of many New England pastures and carries over into the lawn. Grass hungers for the nitrogen that clover fixes. When soil nitrogen is relatively low, clovers grow and grasses hunger.
When soil nitrogen is high, grass crowds clover for sunlight and, if soil is dry, moisture. When nitrogen is low, clover can hold its own, crowd grass, and do its thing. Now comes the interesting part: when ‘White Dutch’ clover is grazed or cut, its nitrogen-fixing bacteria go into overdrive, fixing more nitrogen to replace the lost clover foliage. The bacteria depend on the sugar produced by photosynthesis, so they want to stimulate replacement of the foliage where photosynthesis takes place. As the clover regrows, it has a nitrogen advantage over the grass, so clover crowds the grasses. As nitrogen slowly seeps from the clover roots, the grasses begin to recover and crowd the clover.
So if you harvest lawn clippings for garden mulch, you move a really good balance of soil nutrients to your garden and stimulate more nitrogen fixation and more uptake of mineral fertility nutrients.
Where clover (and dandelions) seem few and far between the grass plants, you might try a light dressing of limestone, or, better, if you can get it, dolomite. In my experience, this tends to foster particularly good growth of the clover and appears to stimulate germination of dormant clover seed. Limestone and dolomite each improves soil structure and moisture-managing abilities of the soil and compensates the acidity common to soils in the Northeast.
So there you have it. With a balance of dandelion, grasses, and clover, your lawn can fertilize your garden while providing soil cooling and water conservation. Between mowings, dandelion and clover blossoms foster pollinators while feeding the adult insect species whose babies eat, slurp, or parasitize some of the pests of your vegetables. In spring, you get early greens when folk wisdom and science both say they are particularly healthful. You can provide more or less continual pollen for desirable insects by staggering your mowings. Growing a few beneficial flowers, such as alyssum, right in your garden also can help cover gaps from mowing.
This story is part 2 in a two-part series about common yard plants that benefit the garden. Part 1 focused on dandelions.
