It makes sense to be cautious about sowing seed after using weed killer. Certain herbicides can harm sprouting seeds and young plants. However, while you must wait several months to sow seed after applying some weed killers, you only need to wait a few days after applying others. The reason for this difference lies in the effect of the active chemicals in the individual products. Read the label carefully and follow all the directions when applying a weed killer.
Pre-emergence weed killers prevent seeds from sprouting. They create a chemical barrier on the soil surface that suppresses seed development. What this means is, if you sow your own seed after applying a pre-emergence weed killer, the seed isn’t likely to grow. However, some pre-emergence products only affect grassy weeds, so you can safely sow most vegetable and flower seeds after applying these herbicides. The same doesn’t apply to reseeding or overseeding your lawn. Grass seed won’t sprout until a pre-emergence weed killer has decayed and become ineffective. For example, it isn’t safe to sow lawn seed until four months after applying a crabgrass preventer.
Sowing Seed After Applying Glyphosate
Sowing seed after applying a pre-emergence weed killer disturbs the chemical barrier on the soil surface, which means that weed seeds may germinate too.
You can sow seeds in as little as a week or even sooner after spraying glyphosate, a systemic, nonselective weed killer. Glyphosate moves from the leaves to the roots of plants, destroying the entire plant, but leaving no residue in the soil. The chemical affects many types of plants, including weeds, grasses and desirable plants, but after the liquid is absorbed into the plant, it doesn’t pose any further threat. You can safely sow ornamental flower seeds a day after spraying with glyphosate and grass and vegetable seeds, three days after, even though the herbicide takes up to seven days to destroy weeds. If you remove the dying weeds too soon, live roots could remain in the soil, ready to regrow. Another systemic weed killer that doesn’t affect seeds is pelargonic acid.
Many selective weed killers leave little or no trace in the soil, and they target certain plants while leaving others unharmed. Generally, these types of herbicides destroy either grassy weeds or broadleaf weeds. You can safely sow most seeds in your vegetable or flower patch a day after applying selective herbicides, such as sethoxydim, clethodim and bentazon, for grassy weeds. These herbicides only affect your desired plants if the plants belong to the grass family. For lawns, herbicides that destroy broadleaf weeds are effective, but it isn’t safe to reseed until a month after applying these products, unless the label states differently.
Selective weed-killers are often garden-friendly. They destroy grassy and broad-leaf weeds without leaving a trace in the soil. They are ideal for killing weeds in lawns while leaving other plants unharmed.
Planting your grass too soon after using some weed killers can ruin your lawn. In some cases, the seeds may fail to grow if traces of the weed killer are still in the soil. Some herbicides also damage sprouting grass seeds and young plants. You will need to be cautious about how you space the period between weed killer application and grass sowing.
Sowing grass seeds after applying selective weed killer
Knowing how long weed killers stay in the soil helps you determine the ideal time to sow your grass seeds. Besides giving the weed killer time to decay, you also need to allow the weeds to die. Some weed killers evaporate within two to three days, while others take a longer time.
Glyphosate is a systematic weed killer that destroys whole plants from the roots to the shoots without leaving any residue in the soil. The herbicide affects several plant types. These include grasses and any other desirable plants that accidentally absorb the chemical.
Pre-emergence weed killers work by creating a chemical barrier on the soil surface that prevents weeds from sprouting. They kill the weed at the initial stages and often affect plants of the grass family. That means if you plant your grass soon after applying this type of chemical, the seeds may not germinate until the weed killer becomes ineffective.