How to Thicken St Augustine Grass

St. Augustine is a warm season turf that is loved for its dense coverage and big, soft blades. It can be a challenge to maintain, but with a dedicated routine, you can keep the lawn green and thick.

Growing Conditions For St Augustine

The best way to achieve a healthy lawn is by focusing on the growing conditions. This includes:

  • Sunlight – This sun-loving grass thrives in the heat of spring and summer. Although it’s more shade tolerant than other warm season grasses like Bermuda or Zoysia, it prefers to be in full sun.
  • Soil – St. Augustine grass was bred to grow in sandy, coastal soils, so it likes ground that drains well but retains moisture. Good aeration, nutrient profile, and a slightly acidic pH balance are also important to keeping the grass healthy.
  • Water – Since the grass loves high temperatures and direct sunlight, it needs to stay well-hydrated. St. Augustine grass has higher watering requirements than other warm season grasses.

Can You Reseed St Augustine Grass?

St. Augustine was intentionally bred as a new species of grass, and its seeds don’t grow into mature grass systems. You can only purchase St. Augustine as sod or grass plugs. Sprigs from a grass system can be propagated, but they don’t do as well as sod or grass plugs, which have robust root systems that are established and ready to spread.

The grass spreads by stolons, above-ground runners that set down roots as they grow longer. This makes them easy to establish, especially when the growing conditions are right.

How Can You Encourage St Augustine To Grow?

Fertilizing Lawn

Grass growth has a lot to do with weather: St. Augustine comes out of dormancy when soil temperatures remain above 60 degrees, and it thrives in temperatures above 80.

Otherwise, keeping to a consistent annual maintenance schedule is the best way to keep the grass green and lush. Your location’s climate will dictate exactly when in the year you should do one or another maintenance activity. When you follow your schedule, you’ll stay in sync with the grass rather than waiting for it to be stressed to attend to it.

Fertilizer For St Augustine

Your lawn will appreciate different nutrients at different points in the year. The first application should come at the end of winter when your grass will soon be coming out of dormancy. You won’t have any applications in midwinter, since the grass is dormant and can be stressed when excess nutrients are applied.

Potassium can be put down in late winter as a soil preparation, but it will be in early spring when you should apply a fertilizer with nitrogen and phosphorus. The NPK ratio of a fertilizer will let you know the formula’s balance, and different products will be applied at different times of the grass’ growing seasons. Slow release NPK fertilizer is best for St. Augustine lawns, in either synthetic or organic solid forms like granules and compost.

Be sure to only apply phosphorus fertilizers in the early spring when the grass is coming out of dormancy. The phosphorus is used for root development, and once roots are established, it won’t be absorbed much. Extra phosphorus in the soil can make iron unavailable by raising the pH and making the soil more alkaline, which bonds iron molecules to other particles and can’t be absorbed by the roots.

Iron and nitrogen can be applied throughout the growing season to give your grass a burst of green production as necessary. Too much nitrogen can prompt too much growth, so an application of an iron supplement in midsummer will keep your growth and thatch levels manageable while greening up the lawn.

Herbicide For St Augustine

Lawn Herbicide

Dense turf is an important way to out-compete weed growth, but sometimes weeds slip under the radar. Grassy weeds like crabgrass, rye, or poa annua can show up and crowd out your St Augustine. Targeted herbicides at the right time of year will help your lawn stay free of unwanted growth.

Pre emergent herbicides

Pre emergent herbicide should be put out at the end of winter or in very early spring for cool season weeds, and again at the end of summer to prevent fall and winter weeds from establishing. Your pre emergent application will target grassy weeds, which then helps your grass grown in thick and not leave as much space for potential summer weeds.

A pre emergent needs to be applied before daily temperatures reach a consistent 55 degrees, at which point weeds like crabgrass will start to germinate. Grassy weeds get mixed in with your lawn so much that it’s very difficult to target them once they’re established.

Post emergent herbicides

In spring and summer, once your grass has fully grown in, you can apply a post-emergent herbicide to any broadleaf weeds, like dandelions and clover, that grow in after the grass does. Some fertilizers, particularly weed and feed products, contain weed killer that targets those midseason weeds.

Mowing An St Augustine Lawn

Mowing Lawn

From spring to fall, St Augustine lawns need to be mowed regularly once a week. If the grass gets too tall, it will shade itself and the bottom portions of the grass won’t receive enough sunlight. If it gets cut too short, it will stress the grass. It’s generally recommended to keep St Augustine grass at about 4 inches in height, on the taller side compared to many other turf grasses.

Avoid mowing when the grass is wet so it gets an even cut. Leaving lawn clippings on St Augustine builds the thatch layer that helps protect the stolons, but if you have too much thatch building up, feel free to collect the clippings with as you need to (more on that below).

Watering Schedule For A St Augustine Lawn

St Augustine grass needs a lot of water! While it will quickly show signs of stress, it will bounce back from periods of dryness with proper care. Your lawn needs about half an inch of water at least twice a week during the spring, summer, and fall, and about once a week during the winter.

This usually is about 30 minutes of watering per session, and the grass likes large servings less frequently. This allows the roots to dry out; you don’t want to let them get too wet, or they may get damaged by fungal growth or root rot.

Aeration For A St Augustine Lawn

If the lawn looks like it’s not growing in well, with pale, patchy, short, or flat blades, your ground may be too compacted for the grass. Compacted soil can be easily fixed with a core aerator, which will get work oxygen into the topsoil and allow better water penetration. Both air and water will encourage better root growth and more stolon production for even coverage, with blades that are upright, firm, and dark green.

Should I Dethatch My St Augustine Grass?

A St. Augustine yard may need to be dethatched once a year, but in general, the thatch is an important part of the turf that protects and stabilizes the grass’ stolons, or runners, which are like long vines. They do put down their own roots on each node, but the nodes are connected along the runners back to a main root system that will feed it throughout its life.

Dethatching Lawn

The end of winter and beginning of spring would be the best time to rake up any dead grass or excessive thatch buildup, just before the grass comes out of dormancy and about to enter its most active phase of growth. When you do have to dethatch, use a soft rake and add new topsoil to stabilize and protect the stolons and their roots.

Pests and St Augustine Grass

Insects like ants, aphids, and other pests are most active between the late spring to the end of summer. Since you’ll be out in your lawn caring for the grass regularly throughout the year, you are the best monitor to notice if there’s stress or dieback in your lawn from an infestation of some kind.

A healthy lawn is somewhat pest resistant, but if you notice bare spots, yellowing, or thinning, a close look will let you know whether you’re dealing with insects or another issue. You should generally wait to see a pest before applying anything, since each will have a different way to be dealt with.

Diseases In St Augustine Grass

St Augustine is especially vulnerable to fungus and root rot, since it likes a lot of water. Although it likes well-drained soil, it also doesn’t like to dry out completely. Thatch helps keep the ground from losing too much moisture, but peat moss is known to be especially good at supporting moisture control, so the grass stays well-hydrated while combating fungal growth.

Signs Of A Stressed St Augustine Lawn

When your St Augustine grass is stressed from compacted soil, as mentioned above, it grass will be pale, flat, and thin. Other color indicators help you know that the lawn is stressed:

  • Yellow grass – Grass that’s turning yellow may be caused from a few different factors. Stress from pests, root rot from too much water, or a nitrogen or iron deficiency can all lead to your grass turning yellow. Fungus may also be a cause or yellowing and dieback. If it’s yellowing but not dying, it’s likely an iron deficiency.
  • Brown or tan grass – Usually, dry-looking grass means dehydration. When St Augustine gets dehydrated, it sacrifices grass noes on the inner stolons to pass resources down onto younger grass blades further down.
  • Purple grass – St Augustine can turn a purple color when it puts up grass blades with seeds, a sign the grass is stressed and trying to reproduce (which, as noted, it can’t). When it goes to seed, it’s usually due to excessive cold or dehydration, but it can also be due to low nutrients in the soil.

When you notice any these different signs in your grass, or if you think it’s just not growing well, it’s important to consider all the environmental factors before deciding on a solution to be sure you’re targeting the right problem.

How Do You Fix St Augustine Grass That Is Thinning?

Watering Lawn

If your St Augustine grass is thinning, either from a lack of water, compacted soil, or low nutrients, investigate the source of the thinness. Fungus and pests may be sources of thin or patchy growth as well. Making sure the grass is in good environmental conditions is the best way to encourage your lawn to grow back in thick and dense.