Three types of weed

An ephemeral weed is a weed that has several life cycles in a growing season.

An annual weed is a weed that completes its life cycle in a growing season.

A perennial weed is a weed that lives through several growing seasons.

Figure 13.4 Young cleavers. Seeds on older plants stick to the fur of animals

The range of weed species includes algae, mosses, liverworts, ferns and flowering plants. These species display one or more special features of their life cycle which enable them to compete as successful weeds against the crop, and cause problems for the horticulturist.

  • Ephemeral weeds, such as groundsel and chickweed, produce seeds through much of the year. Weed seeds often germinate more quickly than crop seeds and thus emerge from the soil to crowd out the developing plants. Their seeds germinate throughout the year. Their roots are often quite shallow.
  • Annual weeds, such as speedwells, annual meadow grass and fat hen, are similar to the ephemerals in their all-year round seed production. Their seeds take longer to ripen those of ephemerals. They may develop deeper roots than ephemerals.
  • Perennial weeds, such as creeping thistle, couch-grass, yarrow and docks, have long-lived root system. Each species has an underground organ that is difficult to control. The creeping thistle has long lateral roots; couch has long lateral rhizomes; yarrow has long lateral roots and docks have deep, swollen roots.

Whilst seed production may be high, especially in the last three of the four above-mentioned species, it is the spreading underground organs that present the main problems to horticulturalists. The large quantities of food stored in their vegetative organs enable these species to emerge quickly from the soil in spring, often from considerable depths if they have been ploughed in. The fragmentation of underground organs by cultivation machinery often enables these species to propagate vegetatively and increase their numbers in disturbed soils.

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