Without the luxury of carrying out a full soil analysis, it is difficult to understand with any degree of accuracy which nutrients should be applied to ensure the new grass sward has all the nourishment it requires. A suitable pre-seeding fertiliser that contains appropriate quantities of nitrogen, phosphorous and potassium should, therefore, be applied.
Nitrogen fertiliser
The main nutrient required by young plants is nitrogen (N): while this essential element offers little beneficial assistance to the germinating grass seed, it is critical for the ongoing development of the emerging young plants. However, it is important that nitrogen is supplied in the right form and quantity as the wrong source or amount of nitrogen can be harmful to developing plants.
The ratio of N applied should be 10% or lower and of an organic or urea-based form. Most soils will contain small amounts of nitrogen in the form of organic matter, but this is never enough to support a healthy lawn. You will need to apply further amounts of nitrogen over the growing period in response to growth rates, soil drainage and any nutrient losses incurred as a result of leaching.
Phosphate fertiliser
If nitrogen is the main nutrient required by young plants, phosphate (P) is the key element for the germinating seed as it is essential for root development and helps to make trace elements available to the developing plant. Phosphate also assists with future disease and drought stress prevention.
Tell-tale signs of phosphate deficiency are a purpling tinge to the plants which will cause stunted growth and dormancy leading to the wilting and death of the plant. While a soil test may indicate there is plenty of phosphate in the soil, a significant percentage of this will be retained in different soil ‘pools’, making it largely immobile and, therefore, not readily accessible to the developing plant.
These reserves will be used over time (as the plant develops a wider root network), but during the early days of the new plant’s life, an alternative, more readily available and soluble source of P should be made available in the upper layer of the soil profile. This can only be achieved by applying a new source of phosphate, but it is important not to over-apply as this will create additional inaccessible reserves which will subsequently become susceptible to rainfall-induced run-off losses.
Potassium fertiliser
The third major nutrient required by young grass plants is potassium (K). As with nitrogen, potassium has little beneficial effect during germination but is essential to preventing disease as the seedling develops.
While potassium applications show little immediate aesthetic improvement to the new grass sward, the depletion of this key nutrient can be devastating over time as plants become more susceptible to disease, so levels must be retained: the amount of K applied should be increased in the summer and autumn when the plants will use it to assist with drought stress.
The plants will continue to tap into these reserves during the winter months to ward off disease pressures and to counter the effects of low light levels – hence why a soil test carried out in the autumn will show a suitable amount of potassium present, but by spring these reserves will be depleted.
Quick-start fertilisers
Germinal’s two main pre-seed fertilisers, G1 Quick Start (6-9-6) and G2 Quick Start Extra (10-15-10), provide the ideal ratio of N, P and K for new seedbeds, with the latter ideal for use on particularly impoverished soils. These products are best utilised when applied to the seedbed prior to seeding taking place. Ideally, they should be worked into the top inch of soil so that they can be sought out and accessed by the developing seedlings.
This is preferable to applying post-seeding as it gives time for the individual nutrients to break down into their available formats prior to the introduction of the grass seed, thereby reducing the risk of seed scorching or ‘lazy’ root development. In situations where it isn’t possible to apply the fertiliser prior to the grass sward developing (e.g. when overseeding an existing sward), it makes sense to delay seed application until a few days after the fertiliser has been applied so that the nutrients have broken down into their accessible forms prior to the introduction of the fresh seed.
Grass Aftercare
In ideal growing conditions during the peak growing season (typically late May to early September), the application of a pre-seeding fertiliser will enable new grass plants to bolt away in quick order. After six or seven weeks, or once the grass sward has been mown three or four times, a low-nitrogen grass feed should be applied to ensure the plants continue to thrive.
Avoid the temptation to apply any sooner than this, as the young plants won’t be strong enough to withstand the scorching risk associated with direct nitrogen treatment. This rule also applies to herbicide applications: don’t be tempted to apply a chemical treatment too soon as the young plants won’t be mature enough and could be detrimentally affected. Please feel free to contact our amenity grass seed experts if you have any questions.