Why is my grass seed not germinating?

Grass seed that has not come up has usually run into one of six problems: not enough time, not enough water or too much, no contact with loose soil, a weed preventer still in the soil, the wrong season for that grass, or old or poor seed. You can rule most of them in or out in a few minutes with the seed bag, a calendar and a look at the soil.

1. It has not had long enough

Check the calendar before anything else. Tall fescue and perennial ryegrass germinate in about 4 to 7 days, while most Kentucky bluegrass cultivars need 10 to 14 days.^[1] Centipedegrass can take 14 to 28 days.^[1] EPA's seeding guidance gives a wide overall range: grasses should emerge within 4 to 28 days of seeding.^[7]

Those times assume warm, moist soil. Seeding is held back by unstable soil temperature and soil moisture content during germination,^[7] so a cool spell or a dry week can reset the clock. A fescue and bluegrass mix often looks patchy for the first two weeks because the fescue comes up first.

2. The surface dried out, or stayed soggy

Seed has to stay moist from the day it is sown until the seedlings are up. The rule is to irrigate lightly and frequently until seed germination and initial establishment is complete,^[2] but too much water can wash away or drown the seed.^[2] Once a seed has sprouted, the seedling has little to no drought tolerance,^[4] so one hot, dry afternoon can undo a week of watering.

Too much water causes its own failure. Germinating seedlings are very susceptible to attack from several soil-borne fungi that thrive in wet environments,^[2] which is why it pays to use fungicide-treated seed to combat seedling damping-off.^[2] Seed in low spots that stay wet often rots while the rest of the lawn comes up. Our guide to how often to water new grass seed has a schedule.

3. The seed never reached the soil

This is the most common cause on an existing lawn. Simply applying seed over the top of an existing turf without any soil preparation usually does nothing more than feed birds and wildlife.^[2] Seed needs loose soil around it so that when the germinating seed sends down its root, the plant will quickly have access to water and nutrients.^[3]

Scratch the surface in a bare spot. Seed sitting on thatch, hard clay or leaves points here, and so does seed that washed into the low end of a slope after a storm. A light straw mulch helps on both counts: it is meant to help conserve moisture, reduce seed movement from rain and irrigation, and further enhance establishment.^[3]

4. A weed preventer is blocking it

Crabgrass preventers stop seeds from germinating, and they work on grass seed too. Henrico County's Extension office says of the common preventers: "All of these products, with the exception of Tupersan®, will also prevent turf grass seed from germinating."^[6]

The waiting periods are long. Turfgrass seeding may be restricted for 60 to 120 days following treatment with preemergence crabgrass preventers,^[5] and most herbicides require a 30 day wait before turfgrass seeding is allowed.^[5] After a fall preemergence herbicide aimed at annual bluegrass, seeding must be delayed for two to four months.^[5] Overapplying makes it worse: if excessive rates are applied, the herbicide persists for several months and may prevent turfgrass seedling establishment.^[5]

Warm-season seed has an extra trap. Some starter fertilizers include a crabgrass preventer made with siduron or mesotrione, which does not harm germinating cool-season grasses, but siduron and mesotrione kill warm-season turfgrass seedlings.^[5] Check the active ingredients on the bag before seeding bermudagrass.

A uniform failure across a treated area, with seed still visible and unsprouted, is the classic sign. Check "weed and feed" products too, and ask your lawn service for its application records.

5. The season does not suit the grass

Each type of grass has its window. In Virginia, cool-season grasses are ideally established in the late summer to early fall, with spring as the secondary time,^[4] and warm-season grasses are ideally established in late spring to mid-summer.^[4] Bermudagrass sown in October, or fescue sown in a July heat wave, may sit in the soil without sprouting or come up and die. Seed sown in late fall can also stall until spring.

Something may have come up that is not your grass. Annual bluegrass germinates around the same time desirable cool-season turfgrass is seeded,^[5] so check that the seedlings match what you sowed.

6. The seed, the rate or the soil

Read the bag. Virginia law requires lawn seed labels to show the percentage of germination for each named grass and the month and year the germination test was completed,^[8] and cool-season lawn seed carries a sell-by date no more than 15 months from the germination test.^[8] Seed well past that date, or kept in a hot garage, often comes up thin.

Rate matters both ways. For tall fescue on bare soil, aim for seeding somewhere between 10-15 seeds per square inch,^[3] and seed piled thickly fails as surely as seed spread too thin.

If everything else checks out, test the soil to determine if low pH or nutrient imbalances are responsible.^[7]

Fixing it

Reseed only after you have fixed the cause, and only if there is still time in the season. If a herbicide is to blame, wait out the label interval. For overseeding failures in particular, see why grass seed did not come up after overseeding; for spots that fail every year, see why a lawn has bare patches.

Stop and call a pro if

• A herbicide is the likely cause and you cannot tell from the labels how long to wait.
• Water runs across or pools on the seeded area, which means the grade needs work before reseeding.
• Seed has failed twice in the same place despite good soil contact and watering.
• The soil test shows a problem across the whole lawn, or the area is too big to rework by hand.

Browse more lawn and landscaping answers, compare sod and seeding services, or find lawn and landscaping businesses near Blacksburg. To have the area reseeded properly, describe the job once and local businesses can quote it.