How to Use Seaweed on Your Lawn

A lawn is thousands of small plants packed shoulder to shoulder. They get mowed every week, walked on and exposed to high temperatures all summer long, so a lot depends on how deep their roots go. That pressure is why kelp is worth using on grass: kelp is a seaweed packed with natural growth compounds that help plants build roots and cope with heat and dry spells. Want to know how often to spray liquid kelp on your lawn, when in the season it does the most good and which mistakes to skip? Keep reading.

Kelp and Seaweeds are biostimulants

This is the big one. Plenty of people buy liquid seaweed expecting the deep green flush they get from a bag of lawn food, and they're disappointed when it doesn't come.

Kelps and seaweeds are a biostimulant, meaning a product that helps the plant use what it already has rather than supplying the main nutrients itself. (Here's a quick primer on biostimulants vs fertilizer.) It carries small amounts of minerals and a mix of natural growth compounds, but nowhere near the nitrogen your grass needs to stay dense and green.

So keep feeding your lawn and use kelp alongside your regular fertilizer and the compost or clippings you already return. The two work well together. In one glasshouse study on perennial ryegrass, seaweed extract combined with normal nutrients gave the best grass colour of any treatment.

If you aren't sure what your lawn is short on, a soil test from your local extension office costs little and tells you exactly what to add.

When to spray liquid seaweed on your lawn

Timing depends on your grass type.

Cool-season lawns (tall fescue, Kentucky bluegrass, perennial ryegrass, fine fescue) grow hardest in spring and fall.

Spring: Make your first spray once the lawn has greened up and you've mowed it two or three times. In much of the country that's April or early May.
Late spring into early summer: Repeat every two to four weeks. A spray a week or so before the first real heat gives the grass a head start on summer.
Midsummer: If the lawn goes dormant in a drought, pause. If you water and it stays green, a spray every three to four weeks is fine.
Late summer to early fall: This is the most valuable window. Late August and September is when you overseed thin spots and when roots grow strongly in cooler soil. Spray every two to three weeks until growth slows in October.

Warm-season lawns (Bermuda, zoysia, St. Augustine, centipede) grow in the heat. Start after full green-up in late spring and keep to a two- to four-week rhythm through summer, tapering off as nights cool in early fall.

For most home lawns that works out to four to six sprays a year. Best results usually come when applying at night.

How to apply it: hose-end sprayer, leaves or soil

Liquid kelp on a lawn is about as easy as yard work gets. A hose-end sprayer, the bottle-and-dial attachment that screws onto your garden hose, is the simplest tool. You set the dilution, walk the lawn at a steady pace and you're done. No spreader to calibrate and no granules left on the sidewalk.

You can use it two ways:

Foliar spray: misting it onto the grass blades, where the leaves take some of it in. Spray in the early morning or evening, when the grass is cool and the spray won't dry instantly. Skip it if rain is due within a few hours.
Soil drench: soaking it into the root zone. On a lawn, this just means spraying as usual and following with a light watering (about a quarter inch) to carry the kelp down to the roots.

Many gardeners do both in one pass: spray, wait an hour or so, then water lightly.

A few habits make every spray work harder. Mow first, then spray, so you aren't cutting off freshly coated blades the next day. Walk overlapping passes so you don't leave stripes. And keep your mower high: Purdue recommends mowing cool-season grass at 2.5 inches or taller, which shades the soil and supports deeper roots.

Exact dilutions for hose-end sprayers, foliar spraying and drenching are on the KelpEdge™ How to Use page.

Using KelpEdge™ on new seed and established turf

KelpEdge™ fits easily into the spring and late-summer routine above. It's a liquid, so it goes in a hose-end sprayer, a pump sprayer or a watering can for patches, and it can be sprayed on the leaves or drenched into the soil. The particles are very fine (about 4 micrometers), so it won't clog sprayer nozzles or drip lines.

Turf results have been encouraging. In an initial university growth-chamber trial on tall fescue seed, seed treated with KelpEdge™ germinated at 78%, compared with 68% for seed soaked in water alone. Those seedlings also had about 21% more root mass and 19% more shoot mass.

Established grass looked good too. In an initial university field-plot trial on turfgrass, plots treated with KelpEdge™, with no added nitrogen, had about a third more root biomass than untreated plots.

Here's how to put that into practice:

Overseeding in late summer: After spreading seed, water it in with diluted KelpEdge™, then keep the seedbed moist as usual. Repeat once the new grass is up and again a few weeks later.
Spring on established lawns: Add KelpEdge™ to your first spray after green-up, a week or so after your spring feeding, and repeat every few weeks into early summer.
Fall root-building: Keep spraying through September alongside your fall fertilizer, when cool-season roots are growing hardest.

As for what's in the bottle, KelpEdge™ is made from 100% wild Alaskan giant kelp (Macrocystis pyrifera) harvested near Ketchikan and processed within hours of harvest. It's extracted with a cold, mechanical process, with no high heat or harsh chemicals (more on how it's made). Independent lab analysis found 17 amino acids and natural plant growth compounds, including auxins and cytokinins, along with minerals such as potassium and calcium. Heavy metals tested well below EPA limits, which matters on a lawn where kids and pets play. It's OMRI Listed for organic use.

Common mistakes with liquid kelp on lawns

Spraying in midday heat. The spray dries before the grass can use it. Go early or late.

Skipping fertilizer. Kelp supports a well-fed lawn; it can't stand in for one. Keep your usual feeding schedule, and look into research on seaweed and stress: a review in Frontiers in Marine Science reported that seaweed extracts improved turfgrass growth above and below ground, and that works best on grass that already has the nutrients it needs.

Giving up after one spray. Kelp works through steady, repeated use during the growing season. Plan on a series of sprays, then judge the lawn by fall.

Spraying dormant grass. Wait for green growth. Brown, sleeping turf won't respond.

If your lawn could use deeper roots and a better start for new seed this fall, add a hose-end sprayer of KelpEdge™ to your spring and late-summer routine: get KelpEdge™ here.