How To With Fertiliser

Fertilisers can be confusing as we now have access to a wide variety of sophisticated products with specialised formulations.

The thing to remember however, is that all plants planted in well-composted soil (not negotiable at all), also need additional nutrition, like the three main macro elements to grow well.

In the main, we need to kick off the growth of most plants after their winter respite with:

(N) Nitrogen: ‘the leaf maker’ (the first number)

(P) Phosphorus: ‘the root maker’ (the second number)

(K) Potassium: ‘the flower and fruit maker’ (the third number).

All three are present in a different NPK analysis in any bag of commercial fertiliser.

Fertilisers can be organic, meaning their key ingredients are either poultry manure or seaweed with added fishmeal and humic acid. These are slow-releasing and re-application is between four to six weeks. Fertilisers can also be synthetic which deliver high feeds of NPK plus some added trace elements. They give fast results but need to be applied more often. Unless you are a completely organic gardener, it is a good idea to use both.

You can for instance apply slow-releasing organic fertilisers formulated for lawns in early spring combined with a thin layer of lawn dressing to wake up your lawn and follow it up with a fast-working chemical fertiliser. The same can work for established shrub beds using a slow-releasing formulation for flower production plus a fresh layer of mulch, alternating with a follow up of a synthetic product high in potassium later on.

Fertilising tips

  • Lawns – never fertilise bone dry lawns. Mow and irrigate it the day before. Stick to the quantity of fertiliser per square meter given on the package, and if you are feeding a large area, use string to mark out where you have done it as you go along. More than is needed is a complete waste! Water immediately afterwards to wash the fertiliser into the soil.
  • Shrub beds – spread out granular or pelleted fertiliser evenly over the root areas of plants. Do not let it collect in a heap around their stems as it might cause them to burn. After fertilising, water well applying a layer of mulch afterwards.
  • Water soluble fertiliser – when spraying with a pressure pump sprayer can, be sure to spray both sides of the leaves. Water soluble fertiliser can also be applied with a watering can as a soil drench. Always discard excess mixed fertiliser.
  • Keep fertiliser bags sealed properly and locked away from kids and pets.

What to feed in August

Feed winter-flowering bulbs that are dying down, with specialised bulb food. This specialised fertiliser can also be used to feed summer bulbs in the garden as well as those you grow in pots like amaryllis.

Start feeding hydrangeas with acid-loving plant food – a specialised fertiliser for blue flowers.

Feed tropical as well as deciduous fruit trees with a formulation high in potassium like 4:1:6.

Feed roses after pruning with a specialised formula for roses to enhance lush foliage, bud formation and colour like 8:1:5

Plants like azaleas, gardenias, brunfelsia and lemon trees, sometimes need a spring boost with a trace element water-soluble product to correct yellowing and blotching foliage. Follow up afterwards with a general fertiliser for fruit and flowers.

Revive focal container plants (which do not need re-potting yet) by removing the top layer of old potting soil and replacing it with a mix of fresh potting soil and compost. Feed it with a slow releasing general fertiliser, water well afterwards and add a layer of mulch.

When preparing new areas for planting in a bed, dig one bag of compost and a root builder like superphosphate or bone-meal into every 2m2 of the bed.

A growth stimulant containing fish emulsion is essential to have around to give seedlings and newly rooted cuttings a boost before they are planted out into the garden.

The Gardener