Hydroseeding Buffalo yards, slopes and fresh-dug ground

What's in the tank, and the fertilizer rule it follows

A hydroseeding slurry has four working parts. Seed is the obvious one. Wood-fiber mulch, made from natural wood and usually dyed green, gives the seed a damp cover and shows where coverage is thin; New York's erosion-control standards list it at 50 pounds per 1,000 square feet when it serves as the mulch by itself. A tackifier glues the fibers to the soil and to each other so wind and rain don't strip them. Fertilizer, and lime where the soil needs it, rides in the same load. The state's guidance for small homesites notes that on a hydroseeded lawn, lime and fertilizer can go through the seeder itself.

That fertilizer is regulated. Under New York's Nutrient Runoff Law, the DEC says hydroseeding lawns with phosphorus fertilizer is prohibited, with two exceptions: the area is being hydroseeded to establish a new lawn, or a soil test of that area shows a phosphorus deficiency. So a brand-new lawn on a graded lot can get a starter blend with phosphorus in it. Overseeding a lawn that's already established is different, and phosphorus stays out of the tank unless a soil test shows the ground is short on it.

The same law bans spreading any lawn fertilizer containing nitrogen, phosphorus or potassium between December 1 and April 1. Seed can still go down in that stretch. Fertilizer has to wait for spring.

New-build lots, pool fill-ins and trench lines

Freshly disturbed ground is where hydroseed earns its keep, and each kind brings its own problem to solve before any seed goes down.

• New construction lots. Months of trucks and equipment pack the subsoil hard. The DEC's permanent-seeding standard calls for chiseling or disking severely compacted areas to at least 12 inches to give roots a rooting zone. Skip that on a new home site and grass over the packed spots stays thin and browns out first in a dry spell.
• Pool fill-ins. The fill under the old pool has to be placed in compacted lifts before the topsoil cap goes on. If it wasn't, the old pool footprint keeps sinking and takes the new lawn with it.
• Sewer, water and conduit trenches. A trench across a yard leaves a long, narrow strip that's fussy to sod and easy to spray. Backfill compacted in lifts and left slightly crowned settles flush instead of into a trough. The same goes for water service and electrical conduit runs.

Topsoil depth matters on all of them. For a mowed lawn over silt loam, loam or clay loam, the state's topsoiling standard sets a 4-inch minimum; over deep sand it's 6 inches. That standard also says topsoil shouldn't be spread while it's partly frozen or muddy, which is why a spring job here sometimes waits on the ground rather than the calendar.

When to hydroseed in Erie and Niagara counties

Late summer is the sweet spot. Cornell Cooperative Extension names August 15 to September 15 as the prime window to seed a new lawn in New York. The soil is still warm, nights are cooling off, and the summer's crabgrass is near the end of its run instead of just getting started. The state's erosion-control standard makes the flip side plain: late June through early August is a poor time to seed, and parts of a midsummer seeding can fail from heat and drought.

Fall has a hard edge. The National Weather Service office in Buffalo defines the growing season as ending at the median first fall freeze, and it stops issuing frost and freeze alerts on October 21 for Niagara and northern Erie counties and on October 11 for southern Erie County. Grass sprayed in mid-September gets several weeks of rooting before that. Seed sprayed after the soil turns cold behaves more like a dormant seeding, sitting through winter and sprouting in spring.

Spring is the second window. Once the ground has dried enough to work, seed can fill in well, but it grows up alongside spring weeds and heads into July heat with young roots, so it needs steadier watering than a fall seeding. Tackifier has its own limits too: when it's used to hold straw, the state standard says to keep it out of the rain and calls for a 24-hour cure and soil warmer than 45°F.

Slopes and banks: hydromulch, straw or a fiber-matrix blanket

On a steep bank, the mulch matters as much as the seed, and the DEC's erosion-control standards are candid about the tradeoffs. Wood-fiber hydromulch needs no tie-down, but on its own it gives less erosion protection than 2 tons per acre of straw. Straw, by the same standard, gives germinating seed the most favorable microclimate but blows around unless something anchors it. The pairing the standard calls best for grass is straw mulch anchored with 500 to 750 pounds per acre of wood-fiber hydromulch sprayed right over it.

Steeper or longer slopes can take a sprayed fiber-matrix blanket: thermally processed wood fibers locked together by a cross-linked tackifier into a crust-like mat. The standard sets 3,000 pounds per acre for slopes up to 3 horizontal to 1 vertical, asks for 48 dry hours after spraying so it can cure, and rules it out between September 30 and April 1. It also recommends spraying seed first and the matrix second, because a heavy fiber layer can hold seed off the soil.

The standard also keeps sprayed blankets out of concentrated flow such as ditches and channels, and plain hydromulch is weaker than any of them. Where water runs along a swale bottom or a ditch line, it needs an anchored erosion-control mat made for waterway centerlines, or stone, and often a drainage fix upstream, before any seed will hold.

Watering and waiting: the first six weeks after spraying

The seed only does its part if the surface stays damp. Cornell's turfgrass program says to water just enough to keep the surface moist, since heavier watering can float seed and soil right off the spot. In practice that means short, frequent sprinkling, sometimes twice a day in a warm, windy stretch, instead of one long soak. Once seedlings cover most of the ground, let the surface dry between waterings and cut back gradually so roots chase the water down.

Expect the lawn to come up in waves rather than all at once. The ryegrass in a mix shows first, and the Kentucky bluegrass that makes up most sunny-lawn mixes can take weeks longer before it starts spreading and knitting the turf together. A new lawn that looks streaky at three weeks is usually right on schedule.

Hold off on mowing until the grass is at least 4 inches tall, and use a sharp blade, since a dull one tears seedlings out of the soil. About 2 to 3 weeks after the seed comes up, Cornell suggests a feeding of 1 pound of nitrogen per 1,000 square feet. The state's small-homesite guidance goes further on traffic, recommending that new seedlings be protected from use for a full year so a dense sod can form. In a backyard, that means keeping cars, heavy play and dog runs off the new grass through its first season.