St. Augustinegrass Floratam: the shade answer in the warm season

Floratam is the only warm-season species here that keeps a usable stand in real shade, rated 4 of 5. That is its whole reason to exist. The cost is a coarse blade that cannot be cut below 50 mm, the weakest wear tolerance in the warm-season group, and a thatch problem that never goes away.

Shade rating 4 and how it is used

Below four hours of direct sun, hybrid bermudagrass dies, zoysia thins, and St. Augustinegrass persists. It achieves this with a broad leaf blade that captures low light efficiently, and it is rated 4 of 5 for shade among warm-season species, the highest here.

Shade tolerance is conditional on two things. Raise the cut to the top of the band, 75 mm, so the leaf area is maximised. And cut nitrogen by a third in shade, because excess nitrogen produces soft leaf that cannot pay for itself at low light levels and becomes the entry point for grey leaf spot.

Why 50 mm is the floor and 75 mm is often correct

Floratam has the widest leaf blade in this profile set and a stolon system that sits above the soil. The floor is 40 mm and the working band is 50 to 75 mm. Mow it at 50 mm and the lawn looks managed; mow it at 75 mm and it looks like a meadow; mow it at 40 mm and you remove the stolons that carry the plant.

Scalping St. Augustinegrass is the most common way to destroy it. A single pass at 30 mm in summer exposes the stolons directly to the sun and can kill a 20 square metre patch outright, because the stolons have no soil contact and no root system of their own.

Nitrogen, iron and the chinch bug risk

Budget 15 g of nitrogen per square metre per year, split 40:35:25. Push it higher and the turf becomes soft, thatchy and far more attractive to chinch bugs, the insect that kills more St. Augustinegrass in the southern United States than any disease.

The first sign of chinch bug damage is a yellow patch in full sun in midsummer that expands in a ring pattern. Confirm it by parting the grass at the edge of the yellow area and looking for 3 mm black and white insects at the stolon layer. Treating on a calendar does not work; treating on a confirmed sighting does.

Iron at 2 g per square metre is a better colour fix than extra nitrogen on this species, for exactly the reason it is on bermudagrass: colour without soft growth.

Thatch 5 of 5 and the annual programme

Thatch tendency is 5 out of 5. The coarse stolons are high in lignin and decompose slowly, and the high cut means clippings contribute to the mat rather than hurting it. A Floratam lawn that has never been dethatched carries a 20 to 25 mm mat by year four.

Dethatch in late spring after full green-up, taking 5 mm a year rather than everything at once. Follow with 2 mm of topdressing sand. Where the mat is already over 20 mm, plan three consecutive years of 5 to 7 mm passes and expect the lawn to look poor for a month after each one.

Wear tolerance is 2 of 5, the lowest of the warm-season group, so keep paths and play areas off this species.

Questions that come up on this page

Can St. Augustinegrass be grown from seed?

Floratam cannot. It is propagated only as sod or plugs. Any seed sold as St. Augustinegrass is a different, unfixed strain with unpredictable colour and texture.

Why is my Floratam yellow in summer?

Check three things in order: chinch bugs at the stolon layer, grey leaf spot on the leaf blades, and take-all patch in the roots. Chlorosis at the leaf tip with green veins is usually iron deficiency on a high-pH soil.

How often should it be mowed?

At 50 mm, weekly through the growing season. At 75 mm, every 10 to 14 days. The one-third rule is rarely the binding constraint on this species because the growth rate is moderate.

Sources

The public reference material the figures on this page were checked against:

• Purdue Extension
• Illinois Extension
• University of Delaware Cooperative Extension