Weed control is the biggest problem facing plant establishment and one which has no easy solution. Weed seeds are present in many situations and lie dormant, but viable, for long periods. A weedy area converted to wildflowers will have a large reservoir of weed seeds in the soil, ready to germinate when conditions are favorable. In most cases, it is advisable to consider weed control in two phases part of site preparation prior to planting, and as an important component of the post-germination maintenance program.
Before planting, remove existing weeds by pulling, tilling under, applying a glyphosate herbicide, or by a combination of these methods. For additional weed control after site preparation, a soil fumigant may be used, or the area may be irrigated to encourage weed growth and then sprayed with a general herbicide.
In very weedy areas, the following method is suggested: (1) Till soil or spray vegetation with glyphosate herbicide. When using an herbicide, allow vegetation to die, then rake out the dead debris. If perennial weeds such as bindweed are present, using an herbicide is more effective than tilling. (2) Irrigate to encourage germination of weed seeds near the surface; most seeds will germinate within two weeks if consistent moisture is available. Do not till the soil again because this will bring even more weed seeds up to the surface. (3) Spray any new growth with glyphosate herbicide. (4) After raking out dead vegetation, allow soil to recover for 3-4 weeks before planting seed. From our experience, a recovery period of this duration is advisable because extensive use of glyphosate herbicides may cause a delay in germination and in the vigorous growth of seedlings.
Once the seeds have germinated, further weed control is usually necessary. If practical, pull all weeds as soon as they can be identified.
Other successful techniques are spot-spraying with a general herbicide or selectively cutting weeds with a string trimmer. Be sure to remove weeds before they reseed.
Many unwanted annual and some perennial grasses can be controlled with the herbicides Grass-B-Gon®*, Ornamec®* and Fusilade®*. These post-emergents do not affect broad-leaved plants so they can be applied over existing flowers; they are most effective when sprayed on new growth and young plants. Take care to avoid treating areas with desirable native grasses or fescues.
*Observe all precautions and follow manufacturer’s recommendations for application.