Seed preparation
The seed is a small, hard, three-angled brown nut. Store it dry and cool until about two months before you want to sow.
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Herb growing guide
Knotgrass, or prostrate knotweed, is a tough, low annual of paths and trampled ground. Its seed is dormant when fresh, so chill it for a month or two, then sow it on the surface in cool weather and keep it in the light.
The seed is a small, hard, three-angled brown nut. Store it dry and cool until about two months before you want to sow.
Not needed. The dormancy is broken by cold and moisture, not by damaging the coat.
Recommended. Mix the seed with damp sand or place it on damp paper in a closed bag and keep it in the refrigerator at about 4 °C (39 °F) for 4-8 weeks. In an Australian study this raised germination from 12% to over 80%. Alternatively, sow outdoors in late autumn or winter in cold-winter regions and let the weather do the chilling.
Not needed as a separate step; the seed takes up water during stratification.
Knotgrass germinates in cool weather, roughly 5-25 °C (41-77 °F). In tests, day/night temperatures from 15/5 °C to 30/20 °C (59/41-86/68 °F) gave over 80% germination in one population, but germination fell to about half at 35/25 °C (95/77 °F). In temperate climates sow in late winter or early spring; in India and other warm regions sow in the cool season.
Scatter the seed on the surface and press it in. Emergence was highest on the surface, fell by half or more at 1 cm (0.4 in) and almost stopped at 4 cm (1.6 in) or deeper.
Any ordinary garden soil or seed compost. The plant tolerates poor, compacted and somewhat saline soil, but fine, firm soil gives the even contact small surface-sown seed needs.
Keep the surface damp until seedlings are established. The seed still germinated well under moderate drought in tests, but a dry surface stops it.
Leave the seed uncovered. Germination was 92% with a daily light period and 49% in full darkness.
Chilled seed comes up over about three weeks in cool weather. Unchilled seed may sit for months and come up only after a winter.
Sow where the plants are to grow. If seedlings must be moved, do it while they are very small, with a plug of soil, and water well.
Thin seedlings so each has room to spread; stems grow along the ground up to about 60 cm (2 ft) long. Water in long dry spells while young; established plants manage with little care and need no feeding or pruning.
Knotgrass is a widespread weed of crops, pastures, turf and paths, and some populations resist common herbicides. Grow it only where spread does not matter, and check local rules before sowing outside a garden.
It thrives where few plants do: trampled, compacted ground, gravel edges and dry, poor soil. A sunny spot gives the densest mats.
Flowers are tiny and sit in the leaf axils along the stems, so seed ripens a little at a time over a long period. Cut whole stems into a paper bag as the first seeds turn brown, dry them and rub the seed out.
Chill the seed, sow it on the surface in cool weather and grow knotgrass where its spread is welcome.
Fresh seed is dormant and needs light. Chill it moist for 4-8 weeks, sow on the surface and keep it damp in cool weather.
No. Knotgrass is a small, low annual (Polygonum aviculare); Japanese knotweed is a large, invasive perennial in a different genus.
It can. It sheds seed over a long season and colonises paths and lawns, so keep it in a contained area and remove flowering stems if needed.