Success with lawn seed in the subtropics and tropics

On this page:

• Selecting the right seed
• Species not suitable for Queensland
• Using soil stabilising species
• Planting turf seeds
• After planting
• Turf rolls or mats

Selecting the right seed

Much of the lawn seed sold by nationally based chains is unsuited to warmer climates. Many of these products are blends containing 85% to 100% cool-season species. The names on the packages do not normally indicate what the species mix is and may actually claim a deceptive range of climatic adaptation. A species list, using either the common name or scientific name, will normally be shown in smaller print somewhere on the packet.

Seed-grown warm-season turf species that will grow in Queensland

Of these, only green couch, Queensland blue couch and kikuyu seed are readily available. Siro Shadegro was developed as a premium shade-tolerant turfgrass species for tropical and subtropical conditions by CSIRO in Brisbane. The Department of Employment, Economic Development and Innovation (DEEDI) at Cleveland has worked with the licensed seed company to bulk up seed of Siro Shadegro prior to wider commercial release.

Narrow-leaf carpet grass, Whittet kikuyu and bahia grass are coarse-textured and need to be used with caution, as they tend to become invasive.

Although green couch is often sold generically (e.g. Speedy couch), there are some named varieties. Generally, these are more vigorous, denser, a darker green and may have other advantages when compared with common green couch. Examples of these improved varieties include Mohawk, Princess 77, Riviera, Sydney, Savannah, Jackpot, Sundevil II and Mirage.

What´s in the bag?

Purchased seed may be hulled or unhulled, or a mixture of both. Hulled seed germinates faster, but is more expensive.

The purity percentage shows how much of the material in the packet consists of seeds of the labelled species, the remainder being inert material or other seeds. The germination percentage indicates how many live seeds there are in the pure seed fraction. For example, a minimum 98% purity and 75% germination means that the seed company warrants that there is a maximum of 2% inert matter and other seeds present, and that at least three quarters of the seeds are viable.

Seeds are sometimes coated with inert materials to improve their flow or to protect them from being taken by insects such as ants before they can germinate in the seedbed. Other inert additives to a bag of seed may include fertilisers to improve seedling growth and wetting agents or hydro-mulches to retain moisture around the seed. None of these inert materials add to the ability of the seeds to germinate; in fact, when fertiliser is mixed so that it comes into contact with the seeds, there is a risk that it may actually reduce potential germination by killing seeds.

Species not suitable for Queensland

It is surprisingly common for temperate climate species to be found in lawn seed blends sold in Queensland; many are budget blends formulated for southern Australia. Check the packet for the following cool-season turf species prior to purchase, as these seeds will not produce a sustainable lawn under Queensland conditions. Although the seed may germinate well, the seedlings will not persist in our warm climate. Any long-term success with such blends in Queensland will be attributable to the presence of small quantities of green couch seed in some mixes.

Soil stabilisers

Green couch can take up to 21 to 28 days to germinate. This leaves an exposed soil surface. Annual and perennial ryegrasses (annual rye is cheaper, but generally with coarser leaves) can be used to give quick short-term cover and stabilise the soil in winter. In summer, a similar effect can be achieved with Japanese millet (Echinochloa crus-galli).

Apply the seed of the stabilising cover species at about 2-3 kg per 100 square metres, for green couch sown at 1-2 kg per 100 square metres. The winter-sown ryegrass will die as soon as temperatures start to rise in late spring. The summer-sown millet similarly recedes in response to cooler temperatures and close mowing.

Planting turf seeds

Warm-season turfgrass seeds can be sown successfully at any time during the growing season from about September to March. During the summer months, however, evaporation is higher (requiring more regular moistening of the seed bed to ensure germination) and weed competition is generally more severe.

Following are the basic steps to achieving a successful seeded lawn.

1. Start with a clean area. Kill any existing lawn and weeds by spraying with glyphosate (Roundup or similar generic products).
2. Loosen soil to a depth of 10 cm. By reducing compaction, the plant roots are able to penetrate deeper into the soil, giving better drought tolerance.
3. Create a seed bed by working the top 2-3 cm to a fine tilth with a steel rake. Purchased sandy loam can assist in creating a favourable environment for seed germination. Remove any large clods.
4. Adjust the soil pH to 6-7 for green couch (but not for blue couch, carpetgrass or kikuyu). Simple soil test kits are available at nurseries. As many coastal Queensland soils are acidic, it may be necessary to raise the pH with lime for green couch.
5. Apply a lawn starter fertiliser. Rake this in well.
6. Level the soil surface.
7. Sow at the recommended rate. A small amount of sand or sawdust can improve the uniformity of distribution of seeds.
8. After sowing, press the seeds into the surface with light rolling or treading, or cover the seed lightly by working a light straight piece of timber across the seeded area.
9. Water well after sowing. Keep the top 2 cm of soil moist by regular light sprinkling.

Note: Local council restrictions on the use of reticulated water may make it difficult to establish seeded lawns in the absence of alternative water sources. Familiarise yourself with local council by-laws on watering prior to starting your project.

Reducing competition from weeds

If time permits, prepare and water the seed bed prior to sowing. This will encourage the germination of the most precocious seeds. Eradicate the emerging seedlings with glyphosate before sowing.

After planting

• Maintain frequent light irrigation until the seedlings have established.
• Restrict the entry of large pets, particularly dogs, into the sown area until the lawn has closed over.
• Check the seed packet for species-specific mowing instructions. Generally seedlings are not mown until they are 80 mm high. Set the mower height at 60 mm to remove only the top 20 mm. This height can be gradually reduced as the lawn develops.

Turf rolls or mats

Although some home owners prefer the economy of establishing a lawn from seed, particularly if they have a large area to plant, there are advantages to buying turf rolls or mats (sod). Instant turf brings your lawn into active service sooner. In addition, a broader range of product choices are available for particular circumstances, and sod is less vulnerable to drying out and invasion by opportunistic weeds. Vegetatively propagated turf grass selections normally outperform seed-grown forms in standardised research trials in the United States. Additionally, seed-grown selections are more likely than vegetative selections to form large numbers of unsightly seed heads at certain times of the year if not regularly mown.