The benefits of weeds
A light hoeing of young annual weeds will kill them. Photo: Sol Morgan
As I’ve been preparing my beds for planting I’ve been noticing which weeds are occupying my garden. A weed is defined as a plant we don’t want. Mostly that refers to non-crop plants that compete with our crops. But are they really that bad? There are some benefits to having weeds in our garden.
Soil indicators: Many weeds I’m pulling are indicators of healthy soil, like chickweed and fathen. Others indicate that my soil is heavy in places and needs more organic matter, such as buttercup. By learning what my weeds are, I can learn about the state of my soil (check out NZ Common Weeds In Colour and An Illustrated Guide to Common Weeds of New Zealand).
Clover can indicate low nitrogen; English daisy, dandelion, plantain indicate acid/clay; docks prefer wet/clay; fumitory shows high potassium; couch indicates a hard pan; henbit suggests low fertility; and yarrow low potassium. We can then take advice from our weeds and make amendments to our soil as required.
Dynamic accumulators: So what do I do with all those weeds I’ve just pulled? Most annual and some perennial weeds can be composted.
Weeds persist because they’re good survivors. Being able to absorb nutrients from different soil zones gives them an advantage, and as a result they accumulate different nutrients. We can utilise their ability to “mine the soil” by adding them to compost. The greater diversity of plant residues (especially weeds), the greater range of nutrients (and organisms) compost will contain when mature.
Borage accumulates silica and potassium; chickweed holds potassium, phosphorus and manganese; dandelion accumulates sodium, silica, magnesium, calcium, potassium, phosphorus, iron and copper. Docks hold calcium, potassium, phosphorus and iron. Fennel accumulates sodium, sulphur and potassium; stinging nettles contain sodium, sulphur, nitrogen, calcium, potassium, iron and copper. Plantains accumulate silica, sulphur, calcium, potassium, iron and copper. Sorrels contain sodium, calcium and phosphorus. Sow thistle or puha has magnesium, potassium and copper. Yarrow has sulphur, potassium, phosphorus and copper, and even Californian thistle contains calcium, potassium and iron.
Many persistent perennial weeds like convolvulus, dock, couch and thistle are risky to put directly into compost as they may reroot. Put them into a drum of water and turn them into liquid fertiliser. Otherwise dry them out on concrete before composting.
A light hoeing of young annual weeds will kill them. During the summer I simply leave them as mulch, thus gaining their nutrient benefit.
Living mulch: It doesn’t take long for weeds to establish in bare soil. Knowing they accumulate nutrients, we can consider them a kind of green manure, used like lupin and mustard. It’s certainly better to have the soil covered. Weeds can be turned in like green crops and the ground is ready for planting soon after. Some, like chickweed, can stay while a crop like broccoli is growing. Just remove it before it goes to seed.
There are numerous ways you can use dynamic accumulators to improve soil health.
· To increase a specific nutrient. If you’ve had your soil tested and know you are deficient in any nutrient, grow a patch of dynamic accumulators that specialise in that nutrient for a season or two before planting your garden.
· As a cover crop. Because most dynamic accumulators are relatively fast growing and deep rooted, they work well as a cover crop to enrich and aerate the soil or prevent erosion before or between plantings. When you are ready to plant your garden, simply dig them into the soil.
· As a mulch. Many fast-growing dynamic accumulators can be cut back several times a season without serious harm to the plants. You can leave the leaves and stems where they fall or move them to an area where the extra nutrients are needed and use them as mulch.
· As compost. If you prefer a neater garden, cut back or pull up dynamic accumulators and add them to your compost heap.
· As companion plants. Plants located near dynamic accumulators are often noticeably healthier than those that are not. Some dynamic accumulators make more attractive companion plants than others, so do your research before planting anything you are unfamiliar with.
Some known dynamic accumulator plants:
Comfrey, dandelion, meadowsweet, lamb’s quarters, garlic, yarrow, fennel, watercress, purslane, buckwheat, parsley, wild strawberry, peppermint, chamomile, stinging nettle, thistle, vetch, plantains.
Food for thought: I’ve often said when talking of weeds, “you’re better off eating many of the weeds in your garden instead of our cultivated crops.” That’s due to their high nutrient value and lack of pesticides. Some, like milkweed and buttercup, are inedible; chickweed is edible and sweet; others have edible parts. They are worth some reading.
Sol Morgan
