Interseeding Grasses

Choosing Seeds

• Use only grass seed varieties that you know can thrive in your climate, and purchase seeds only from reputable garden centers or extension services. Some grasses are more tolerant of different levels of temperature and moisture, so the types of seeds you choose will vary depending on your climate. If in doubt, contact a professional from an extension service or garden center for help selecting a seed combination.

Weed Control

• Controlling weeds is the most important aspect of interseeding, especially within the first year when plants are becoming established. Most areas to be interseeded are treated with broadleaf weed herbicide at least six to eight weeks before planting. Mowing the newly sprouting seeds is another key to weed control. Any existing weeds or unwanted grasses in the area should be mowed as low as possible before insterseeding, then removed or mowed frequently as the new grasses start to grow. Once the new seeds sprout, they should be mowed no lower than 4 inches to prevent weeds from getting sunlight and water. For species of grass native to your climate, keeping them as long as 8 inches in grazing areas helps fight off weeds.

When to Seed

• Till the soil to a depth of 10 to 12 inches before seeding the grasses. This kills the remaining unwanted weeds. For the seeding process, you can use a drill seed press or a broadcast spreader to distribute the seeds. Seeds should be uniformly distributed to a depth of ¼ to ½ inch over the whole surface. You can seed at nearly any time of year; early spring, after the threat of frost has passed, is the most common. You can also seed after the growing season is over but before the first frost hits; the seeds will sprout up the following spring, and the grasses get a jump on growing before weeds. You can also broadcast seed very early in the year, when the soil thaws during the day and freezes at night, to help incorporate the seed into the soil itself for a strong bloom in the spring.

No-Till Seeding

• If you're interseeding grasses into sod, you won't till the surface, but you do need to eliminate competition from the sod. To do so, you can mow the sod as low as possible or kill it off with an all-purpose herbicide application at least six weeks before seeding. For this type of seeding, you must use a drill seeder to implant the seed into the soil below the sod. The thick layer of dying sod will serve as a type of mulch to conserve moisture for the seeds. All no-till interseeding should be done in early spring, after the final frost has passed.