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Horticulture Questions and Answers

Home  >  Lawn Care  >  Selection, Culture and Care  >  When should I seed a cool-season lawn and what should I sow?

When should I seed a cool-season lawn and what should I sow?

In the Saint Louis area, the best time to seed a cool-season lawn is in the fall, from late August to mid-October with early September being the ideal time.

At this time of year, the soil is still warm so grass seed germinates faster and the cool temperatures favor the growth of cool-season grasses. Additionally, weed development is less of a problem and the newly established turf grass has two seasons of optimum growth before facing a hot summer.

The next best time is March or April while the weather is still cool, but competition from weeds, especially crabgrass can be a problem.

Only preemergents (crabgrass preventers) that contain Siduron or Tupersan can be used when seeding. Others applied at the time of seeding or within their effectiveness window will prevent grass seed from germinating.

Before seeding have the soil tested to determine the type and amount of fertilizer to apply to your lawn. Work the fertilizer and lime, if needed, into the top 4 to 6 inches of soil. Level the soil so the seed bed is firm and free of large lumps. Spread the seed evenly at the recommended rate. Roll the surface lightly to put the seed in contact with the soil or using a rake, lightly rake the seed into the top one quarter inch of soil.

After seeding, water the area well. Keep the surface of the soil moist for ten days to two weeks or until the grass seed has germinated. In warm weather this may require watering several times a day.

When seeding a new cool-season lawn, you should consider planting a mixture of grasses not just a single variety. An ideal grass seed mix provides good color, quality, density, disease resistance, and the ability to adapt well to various locations in your yard. This is especially true if your lawn has both open and moderately shaded areas.

The predominant cool-season grasses used in the Saint Louis area are turf-type tall fescues, Kentucky bluegrass, perennial ryegrass and fine leaf fescues.

The turf-type tall fescues are a marked improvement over the wider bladed Kentucky 31 tall fescue and are better adapted as a lawn grass than Kentucky 31.

Of all of the above, 95/5 mixes of 3 to 5 varieties of turf-type tall fescue (95%) and a compatible variety of Kentucky bluegrass (5%) have become the mixtures of choice in the Saint Louis area and the transition zone for full sun to moderately shaded lawn areas.

Densely shaded areas will require a mixture with a higher concentration of fine leaf fescues and are often marketed as a “shady lawn mix”.

Many area seed companies formulate their own mixes and adjust the varieties in them as improved varieties adapted to this area become available. Many local garden centers carry these formulations.

Proper seeding rates per 1,000 square feet:
        Turf-type tall fescue @ 6 to 8 pounds
        Kentucky bluegrass @ 1 to 3 pounds
        Perennial ryegrass @ 6 to 8 pounds
        Fine leaf fescue @ 5 pounds