Gareth Carter: Soil preparation the backbone of a good lawn

A really good lawn can be obtained only by intensive soil preparation before sowing. Photo / Supplied

Erratic and irregular is the spring season so far in the garden. This week's polar blast did little (in fact was darn right destructive) to help my first summer vegetable plantings. However, the highs, lows and trials of gardening are part of the adventure and with a fine spell (hopefully now arrived as this is published), I will plant some more summer vegetables.

This week the column is focused on lawns. The lawn can be the make-or-break component in the look of a garden. It can be an uphill battle (though not impossible) to have the perfect lawn but to have a pretty good lawn is not such a hard feat.

Some timely maintenance (beyond mowing) each spring and autumn can be enough to take your lawn from average/poor to pretty good.

Sowing

Lawn grasses establish best either in spring from September to November or in autumn, from March to the end of May. The soil is warming and spring rain is providing moisture, so now is the time to get cracking if you want to redo your lawn this year.

A really good lawn can be obtained only by intensive soil preparation before sowing; once the lawn is established it is difficult to level off an uneven surface or eradicate undesirable grass and weed species.

Initial preparation

The first step is to remove all existing pasture-type growth. Most grasses and perennial weeds are effectively controlled with glyphosate-based sprays such as Grosafe Glyphosate, Yates Zero or Roundup. Harder-to-kill species such as blackberry, onion weed and english ivy can be removed with the use of Roundup Tough. The spray is taken in through the foliage, then passed on to all parts of the plant including the roots and rhizomes. Visible effects are a gradual wilting and yellowing of foliage, and brown-off may take 7-14 days or longer, depending on growing conditions.

If topsoil has been brought onto the site it is advantageous not to sow immediately but to leave bare for approximately 2-3 weeks (or longer), allowing any weed seed present to germinate, which can then be sprayed with an appropriate weedkiller depending on the weed type.

It is important at this stage to consider drainage. Most grasses prefer a well-drained loam or sandy loam soil to heavier, wetter soils. Good drainage means better penetration of water and air to the grass roots. It also means moss and hydrocotyle weed, which can thrive in moist lawn areas, are less likely to invade the lawn. On some very heavy soils it is wise to import some sandy loam soil, spreading it over the area 8–10cm deep and incorporate it into the topsoil. In extremely wet situations, permanent drainage may need to be installed. If soil is added, you may need to destroy any secondary emerging weed seedlings. It is worth putting time into preparing the soil to the correct levels and contours. For small areas a rake, fork and spade will suffice but for larger areas a rotary hoe will save time. The soil should be worked up to a depth of about 8cm using a rotary hoe or garden fork until the soil is a fine tilth. Any lumps or clods should be removed or broken down. Level and compact lightly, making the surface as even as you can to avoid humps and hollows. The area should be left to consolidate for a week, walking over the area for grading, raking and destroying weeds plus watering or rainfall will help with this process.
If the soil is still soft and spongy all over, rolling may be necessary. To avoid too much compaction only roll or tread the soil when it is damp, not wet. Rake the area again after rolling or treading.

Grass health and fertiliser

Like all plants, regular feeding will keep grass in good health and the turf thick and more resistant to the invasion of weeds. Fertilising in spring and autumn with a specific lawn fertiliser such as Tui Lawn Force Slow Release will ensure grass remains strong and healthy. In heavier soils, it is beneficial to also fertilise with garden lime once a year. Garden lime should be applied in August or September, 2-3 weeks prior to the application of lawn fertiliser. Garden lime increases the pH of the soil, which makes more nutrients in the soil available to the lawn to use. It also has the benefit of adding calcium to the soil, which plays a major role in the physiology of a plant, strengthening its physical structure, increasing nutrient uptake and protecting it from disease.

When sowing a new lawn, use fertiliser Tui Lawn Force for New Lawns. This specific fertiliser has been formulated for application when sowing seed and for young grass. This blend will ensure you get strong, healthy growth without burning the young grass or seed.

Selecting and sowing seed

There is a wide range of seed blends available to suit the particular requirements or the situation. We recommend a range of seed called Ican Specialty Lawn Seed. This range of seed comes in a range of blends to suit different property conditions these blends include: Everyday Blend, All Seasons Hot & Dry and Premium.

Information is available in the garden centre on these blends so you can decide which one suits your property best.

A calm day is best when sowing grass seed, as seed is small and light. To assist in achieving an even sowing distribution it is recommended that you divide the seed into halves and then spread the first half in one direction and the other half at right angles to it. After sowing, the soil surface should be lightly raked, and on light sandy soils a light covering of Tui Lawn Preparation Mix is recommended. This will help to retain moisture and help to prevent seed from washing away during watering or rain. The soil surface should be kept moist with light watering until seedlings have germinated and are well established. Water the lawn less frequently as the seedlings grow stronger - this encourages the roots to grow deeper.

It is very important that young germinated lawn seed is kept moist, otherwise it will die. If watering may be a problem it would be wise to sow your lawn in small sections over a few weeks. This may seem more intensive work but it is better than having patchy germination over the whole lawn because of inadequate watering.

Establishment care

Watering should be cut down to once a week and when the grass is 3.5–4cm high it should be mown lightly and clippings removed. Ensure your mower blades are sharp for a clean cut. The first mow should not remove more than 10 per cent of the height of the grass. After the third or fourth mow, the cutting height can be gradually reduced. After the first or second mow the lawn should be fertilised with Tui Lawn Force for New Lawns, again using the recommended rates on the bag for new lawns.

If flatweeds such as dandelion, cape daisy, plantain and others are a problem, spraying with Yates Turfix will provide good results.

Putting in the hard work now will have you relaxing and enjoying your lawn in the months to come.

Have a good week.

Gareth Carter is General Manager of Springvale Garden Centre