Identifying Weeds – Garden Weeds

Nature of weeds

Identifying Weeds - Garden Weeds Identifying all the different types of weeds in your garden and understanding their means of survival is the first step towards controlling them organically. It can pay to tolerate some weeds, but the worst offenders must be prevented from growing and spreading at the earliest opportunity.

Annual and biennial weeds

Annual weeds germinate, grow, flower, set seed and die all within one year, and may even complete several lifecycles in a single year. Biennial weeds take two years to complete their life-cycles, forming only leaves in the first year and running to seed in the second.

Annual weeds that go to seed quickly are most adapted to the frequent cultivations that take place on the vegetable plot. Common examples include shepherd’s purse (Capsella bursa-pastoris), groundsel (Senecio vulgar’s), chickweed (Stellaria media), annual meadow grass (Poa annua) and hairy bittercress (Cardaminehirsuta). Other annual weeds commonly seen in the garden include fat hen (Chenopodium album), sow thistle (Sonchus oleraceus), mayweed (Matricaria perforata), speedwell (Veronica spp.), sun spurge (Euphorbia helioscopia) and herb robert (Geranium robertianum).

Biennial weeds such as burdock (Arctium spp.), hogweed (Heracleum sphondylium), ragwort (Senecio jacobaea), garlic mustard (Alliaria petiolata) and teasel (Dipsacus fullonum) are more likely to be a problem among shrubs, herbaceous plants and fruit, and along paths and hedge bottoms. They usually have a deep tap root and overwinter as rosettes of leaves.

Annual and biennial weeds die quickly if pulled out, hoed off, rotavated or mulched (see Tips on Weed Control). However, they ensure their survival by producing large numbers of seeds and it is this that causes the problem. If you are going to make any long-term impact on their numbers you must act before they seed.

Not all the seeds that are shed germinate immediately. They become dormant and are incorporated into the soil. As a result every spadeful of topsoil in the garden can contain hundreds of weed seeds. Every time you cultivate the soil and expose the seeds to light and a difference in temperature, the dormancy of some of them will be broken and a flush of weed seedlings will result. You can therefore avoid problems by digging and turning over the soil as little as possible (see No-Dig Gardening). Use the stale seedbed technique (see Ways to Control Weeds) if you are sowing seeds.

Perennial weeds

These are weeds that persist for more than a year, on lawns, for example. Established plants can be very difficult to eliminate. Some have underground storage organs which enable them to survive if the top of the plant is killed by cultivation or cold. Others produce hardy rosettes of leaves which escape the mower. Many will regenerate from pieces of root or stem as well as (or instead of) seed. It is a weed’s particular means of survival that determines the best method of controlling it.

With tap roots

These have a large simple or branched vertical storage root. Examples are dandelion (Taraxacum vulgar’s), dock (Rumex spp.), comfrey (Symphytum officinalis) and cow parsley (Anthriscus sylvestris). They will regenerate from pieces of root if these are cut up by digging, forking or rotavating, and most also produce many seeds.

Forking can bring roots out whole. However, if this is not a practical means of control, put down a light-excluding mulch for a growing season or rotavate several times. Only very regular hoeing will eliminate such weeds, but they will be most weakened if you hoe them just after they have flowered, when reserves from the tap root have been put into the blooms.

With shallow spreading roots

These weeds, like couch grass (Elymus repens), nettles (Urtica dioica), ground elder (Aegopodium podagraria) and rosebay willowherb (Epilobium angustifolium) spread by storage roots or rhizomes. Each bit of root or rhizome that is chopped off sends up new shoots. Most also produce seed.

The roots can be forked out if they are not too matted. Alternatively, rotavate several times or put down a light-excluding mulch for one growing season. Digging and burying the roots deeply is another possible method of control.

With deep spreading roots

These have storage roots that penetrate deeply and send up new shoots if the top section is removed. Nearly all also produce some seed. Examples are coltsfoot (Tussilago farfara), hedge bindweed (Calystegia sepium), field bindweed (Con volvulus arvensis), horsetail (Equisetum spp.) and creeping thistle (Cirsium arvense).

These weeds are difficult to control. Hoeing or forking can be effective if you are very persistent. A light-excluding mulch will take at least two growing seasons to have any effect. In some situations, a good alternative is to grass over the area and mow it as lawn for one or two seasons.

With runners

These have creeping stems above ground. Plantlets form along the stems and put down roots, finally becoming detached from the parent. Some spread by seed. Examples are creeping buttercup (Ranunculus repens), cinquefoil (Potentilla reptans), ground ivy (Glechoma hederacea), silverweed (Potentilla anserina) and selfheal (Prunella vulgaris).

Such weeds can be controlled effectively by digging them under or forking them out if they are not too matted. On a large area, rotavate several times or apply a light-excluding mulch for one growing season.

With corms or bulbils

These have small swollen storage organs at the base of the plant which can regenerate individual plants if they are spread by cultivation. Examples are lesser celandine (Ranunculus ficaria) and pink oxalis (Oxalis articulata).

These weeds are also very difficult to control as cultivating or hoeing spreads rather than kills the bulbils. To control them, you need to dig up individual plants plus the soil around the roots, which is very time-consuming. The bulbils can survive for a long time underground without dying, but a light-excluding mulch will work if you leave it down for at least two growing seasons.

With low rosettes of leaves

These are mainly lawn weeds, but they can spread to beds and borders. Examples are daisy (Bellis perennis), plantain (Plantago spp.), cat’s ear (Hypochaeris radicata), hawkweed (Hieracium spp.) and yarrow (Achillea millefolium). They form rosettes, which often grow outwards to form a mat of plants, and spread to new sites by seed. Hoeing or forking will easily remove single specimens of these weeds, but once they have formed a mat this becomes hard work. Dig them under if practical or, on a larger area, rotavate several times. Alternatively, apply a light-excluding mulch for a growing season.

02. February 2011 by Dave Pinkney
Categories: Organic Gardening, Weed Control | Tags: , , , , | Comments Off on Identifying Weeds – Garden Weeds


Get every new post delivered to your Inbox

Join other followers: