How often should I water new grass seed?

Water new grass seed lightly and often, enough to keep the top of the soil moist without puddles, until the seedlings are up. Then water less often but for longer, and after the first three to four weeks switch to the deep, infrequent watering an established lawn needs. The weather sets the exact schedule, so check the soil rather than the clock.

Stage 1: from sowing until the seed sprouts

The goal is a surface that never dries out. Irrigate lightly and frequently until seed germination and initial establishment is complete,^[1] but avoid excessive amounts of water because this could either wash away or drown the seed.^[1]

In practice that means short waterings that wet the top layer of soil and stop before water collects. In cool, cloudy fall weather one light watering in the morning may hold all day. On a warm, sunny or windy day the surface can dry by mid-afternoon, and a second short watering keeps the seed going. Your fingers are the best gauge: the soil surface should feel damp, like a wrung-out sponge.

How long this stage lasts depends on the grass: tall fescue and perennial ryegrass usually sprout in 4 to 7 days, most Kentucky bluegrass cultivars in 10 to 14 days.^[4] Keep going until the whole mix is up, not just the first green haze.

Do not overdo it. Keep newly established sites moist but not saturated,^[1] because the newly germinating seedlings are very susceptible to attack from several soil-borne fungi that thrive in wet environments.^[1]

Stage 2: young seedlings

Once the grass is up, it is at its most fragile. Seedling or recently established lawns (less than a year old) have little to no drought tolerance,^[2] so a missed day in hot weather can kill a stand that took two weeks to grow.

Now begin to change the pattern. As establishment progresses, gradually cut back on the amount of water you apply in order to start promoting a deep root system.^[1] Water a little less often and a little longer each time, so the moisture reaches below the shallow new roots and they follow it down.

Mowing is part of this stage. For tall fescue, begin mowing as soon as your new lawn reaches a 3-inch height^[1] and never remove more than one-third of the leaf blade at any mowing event.^[1] Mow when the soil is dry enough to walk on without leaving footprints in it, and skip the watering that morning.

Stage 3: moving to an established-lawn schedule

The extra attention does not last long: newly sodded or seeded lawns require more frequent watering (for the first three to four weeks) than do well-established lawns.^[2] After that, water like an established lawn.

For an established lawn, most turfgrasses require approximately 1 inch of water per week^[2] from rain and irrigation combined during warm weather. Deep and infrequent watering that thoroughly soaks the rootzone to a 4-inch depth^[2] builds deeper roots, as opposed to light and frequent irrigation, which promotes shallow roots and germination of weed seeds.^[2] Given the slow infiltration rate of most Virginia soils, smaller amounts of water applied every three to four days may be required to allow water to enter the soil without causing runoff.^[2]

Henrico County's SMART Lawns booklet lists watering deeply 1-2 times per week as needed^[5] among its practices for established lawns, and it describes a simple check called the "screwdriver test": push a screwdriver into the soil, and if it cannot be easily inserted at least two inches deep, it's time to water.^[5]

Getting the most from each watering

• Water early. The best time is a few hours before or just after sunrise.^[2] Night watering is to be avoided unless it is the ONLY time possible because it greatly increases the chances of fungal diseases.^[2]
• Use the right sprinkler. Choose sprinklers that keep water close to the ground rather than sending a fine mist or spray high into the air,^[2] and set them so they water the seed, not the driveway. A hose-end timer makes the light, frequent stage far easier to keep up.
• Mulch the seed. Consider lightly mulching the seeded areas to help conserve moisture, reduce seed movement from rain/irrigation events,^[3] with small grain straw at about 1 bale/1000 sq ft^[3] and some soil still visible through it.
• Let rain count. If regular and repeated watering is not a possibility, then simply leave the site alone and let Mother Nature provide the moisture.^[3] Skip a watering after a good rain.

Seed is not sod

New sod is watered differently. With sod, larger amounts of water can be applied less frequently because sod provides soil and root mass that hold moisture,^[1] although in hot weather above 80°F, new sod needs watering every day until it roots.^[6] See how often to water new sod for that schedule, and seed or sod in Virginia if you are still deciding.

Stop and call a pro if

• Seed is washing into piles or channels every time it rains or you water, which points to a slope or grade problem.
• Areas stay soggy for a day after watering, or seedlings are collapsing in patches.
• Seedlings came up and then died despite steady watering; see why grass seed is not germinating.
• You cannot water for the first few weeks and the lawn needs to establish quickly.

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