Seed Selection and Blend Design

The seed is the whole point. Everything else in the slurry — the mulch, the fertilizer, the tackifier — exists to help that seed germinate and establish. Choosing the wrong seed for the conditions guarantees a disappointing result no matter how well everything else is done, which is why seed selection follows directly from the site assessment.

What Drives the Decision

Four factors determine the right seed for a job:

Climate zone. The first fork in the road is cool-season versus warm-season grass. Cool-season grasses (tall fescue, ryegrass, bluegrass) thrive in moderate temperatures and are planted in late summer–early fall or early spring. Warm-season grasses (bermuda, zoysia, bahia, buffalograss) want heat and go in late spring–early summer. Planting the wrong category for your climate, or at the wrong time, undercuts the whole job. (See The Science of Seed Establishment.)
Sun and shade. Full sun, partial sun, or heavy shade each call for different species. A sun-loving blend thins out under trees; a shade blend gets scorched in the open. On a site with both, the right answer may be different blends in different zones.
Intended use. A manicured residential turf, an erosion-control cover crop, and a native restoration planting are entirely different seed decisions. Turf is chosen for appearance and durability; erosion-control seed for fast, soil-holding cover; restoration seed for ecological fit, often with required native species.
Site conditions and stress factors. Drought, salt exposure (roadsides, coastal sites), poor soil, heavy traffic — each stress narrows the species that will succeed. The seed has to be matched to what the site will actually throw at it, not to ideal conditions.

Blends vs. Single Species

Most jobs use a blend of multiple species or varieties, and they do it for one core reason: insurance. Conditions across a site are never perfectly uniform, and weather is never perfectly predictable. With a blend, if one species struggles in a particular spot or season, the others compensate and you still get cover. A single species is a single point of failure; a blend spreads the risk.

Blends also let you combine complementary traits — pairing a fast-germinating nurse crop like perennial ryegrass, which provides quick early cover and erosion protection, with slower, more desirable grasses that fill in behind it. The fast grass holds the site while the better grass establishes. This is standard practice on quality work, and it's why "what's in the blend and why" is a fair question to ask any contractor.

Pure Live Seed (PLS)

This is the concept that trips up people moving from residential into spec-driven work, and it's worth understanding clearly. Not every pound of seed in a bag is viable, weed-free seed. Pure Live Seed (PLS) is the fraction that actually is:

PLS % = (% purity × % germination) ÷ 100

So a lot that's 95% pure with 90% germination is about 85.5% PLS — meaning a bag of it contains noticeably less viable seed than its weight suggests. This matters because specifications require seeding rates in PLS pounds per acre, not bulk pounds. A spec calling for a PLS rate is calling for a guaranteed quantity of viable seed on the ground, and meeting it means doing the math and applying enough bulk seed to deliver the required PLS. Get this wrong and you've under-seeded a job that looks compliant on paper. (See DOT and Agency Specs and Specification Literacy.)

The companion to PLS is the seed tag — the label on every quality seed bag listing species, germination percentage, purity, weed content, and test date. The tag is how you verify what you're actually planting, and it's a required submittal on most spec work. No tag means you don't truly know what's in the bag.

Seeding Rate Matters as Much as Species

Picking the right species is half the decision; applying the right amount is the other half. Seeding rate — how much seed per unit of area — is a real variable, not an afterthought:

Too little seed produces a thin, sparse stand that's slow to fill in and leaves room for weeds to move into the gaps.
Too much seed wastes money and can backfire — overcrowded seedlings compete with each other for water, light, and nutrients, and the stand can actually come in weaker.

The right rate depends on the species, the use, and the conditions — a high-traffic athletic turf, an erosion-control cover crop, and an overseeding job all call for different rates. And on spec work, the rate isn't your call at all: it's specified, and it's specified in PLS pounds per acre (see above), which means doing the math to convert from the bulk seed you're actually loading.

Reading the Seed Tag

The seed tag is worth knowing how to read line by line, because it's both your quality check and a required submittal on spec jobs:

Species and variety — confirms you're planting what was specified.
Purity (%) — how much of the contents is the named seed versus other material.
Germination (%) — how much of that seed is expected to actually grow.
Weed seed and other crop (%) — contamination you don't want, especially noxious weeds.
Test date — germination rates decline with age, so an old test date is a red flag. Fresh testing matters.

Together, purity and germination give you the PLS figure. A bag with no tag, or an old test date, tells you to ask questions before you load it.

Getting the Seed Right

Seed selection ties the whole assessment together: the climate and timing come from where and when you're working, the species and blend come from the sun, use, and stresses the site presents, and the rate — on spec work — comes from the PLS math. It's the decision the entire slurry is built around.

For quality seed and custom blends matched to your conditions, visit Hydroseed Supply™.

Next: continue with Matching the Recipe to the Project.