In the wild, plants are nourished by a constant diet of decaying plant and animal matter. But in the artificial environment of the garden, plants need to supplement their diet with fertilisers. Spring is the time to fertilise your garden including any lawns, Australian native plants, roses, citrus trees, vegetables, pot plants and orchids.
Before fertilising, check the pH level of your soil using a pH test kit. If it is too high or low, this could inhibit the uptake of some chemicals (such as iron) so causing deficiencies in the plant, even though the required nutrients are present in the soil. For most garden plants a soil pH of between 5.5 and 7 is satisfactory. Note: pH test kits are available from your nursery.
Types of fertilisers
Fertilisers are divided into two main groups:
- Organic fertilisers, which are derived from plant and animal products and include manures, compost, blood and bone.
- Non-organic fertilisers, which are usually sold in granular or powdered form.
Within these two groups are many different formulations including fertilisers that are for specific plants (such as roses, citrus and the like) and all-purpose fertilisers. Despite the enormous range of fertilisers available, the average garden only needs about five basic types of fertiliser: a complete lawn food; Dynamic Lifter; citrus food; liquid food (Nitrosol); and slow release (such as Osmocote). The role of each of these is outlined below.
Fertilising the lawn
There are many lawn fertilisers on the market and the one you choose is a matter of personal preference. Most brands of complete lawn food will fertilise the lawn well, but ‘Burke’s Backyard’ strongly recommend you do not use Sulphate of Ammonia. This fertiliser is popular for greening up the lawn however it is a high nitrogen fertiliser with little to promote long-term growth and development. Excessive use of this product (or indeed any fertiliser) will have an impact on the soil and so the quality of your lawn.
Dynamic Lifter Green Keeper’s Choice, which is a mixture of Dynamic Lifter and a fortified lawn food, and Scott’s Lawn Builder, which is a slow release fertiliser, are good all purpose lawn foods. Another good all purpose lawn fertiliser is Shirley’s Lawn Food No. 17.
Although not specifically for lawns, many gardeners have reported good results from Osmocote, a slow release fertiliser. Yates Weed and Feed is also useful for feeding lawns. It can be used to get rid of some problem weeds such as Kurnell curse, also known as pennywort (Hydrocotyle tripatita ), in buffalo or kikuyu lawns.
Most of the instructions recommend the application of 5kg to 100 square metres, but if this is too difficult to calculate, try applying fertiliser at a rate of one handful to the square yard. Apply one-half handful one way, then go at right angles with another half handful. If this is too much trouble, mechanical fertiliser spreaders are available at a cost of about $90 each. They can also be hired.
The Scotts Lawn Builder has a hand spreader, which is available at nurseries that stock the fertiliser (cost: around $27). By using a fertiliser spreader you will ensure a perfect result every time as you will spread the fertiliser evenly across the lawn. Lawn foods and some other fertilisers can also be applied in a liquid form via the hose. One such product is the Miracle Grow No Clog 2. Cost: $33.
Roses and citrus trees
Rose and citrus fertilisers are almost identical so there is no real need to have both even if you grow both roses and citrus, such as oranges or lemons, in your garden. Citrus food can be fed to roses and vice versa. Citrus and rose foods can be used to fertilise vegetables as well. Chook poo (such as Dynamic Lifter) is a also good for citrus.
To fertilise a full grown citrus tree spread about 1.5-2 cups of fertiliser under the tree to the drip line of the tree. The drip line is the line of the outer edge of the branches where the drips from foliage would fall. Do not spread the food too close to the trunk as the feeder roots, those that utilise the food, are in the outer areas near the dripline. Fertilise in spring, and repeat the process in late summer, using 1 cup of fertiliser.
Australian native plants
Care must be taken when fertilising Australian native plants, because too much fertiliser, particularly products high in phosphorus, can easily kill them. Natives are pretty hardy in most Australian soils, so if they were never fertilised, it probably wouldn’t matter.
Recommended fertilisers are blood and bone and Dynamic Lifter (not the fortified Dynamic Lifter). Do not use very much. A light handful over a few square metres is sufficient.Note: Not all blood and bone products are of a good standard. ‘Burke’s Backyard’ recommends Yates or Pivot blood and bone as these conform to labelling requirements (100% blood and bone) whereas some other products do not.
There are also special formulations of slow release fertiliser for native plants. One of these is Osmocote Slow Release for Natives which is low in phosphorus.
Most general fertilisers can be used on vegetables but complete plant food is particularly useful. Apply manures and complete plant food to soil when it is being prepared for planting.
Liquid feeds too can be used on vegetables. These should be used to promote strong vigorous growth by making frequent applications to crops (particularly leaf green crops) while they are growing. Note: Thrive, an inorganic liquid fertiliser is now available in a resealable plastic bag which overcomes problems experienced in the past when the cardboard box deteriorated.
Fertilising plants that are growing in pots or containers is crucial because they grow in potting mix which becomes depleted of nutrients. Slow release fertilisers, such as Osmocote plus Nutricote, are recommended for pot plants.
Nine month slow release fertilisers are particularly useful for pots if applied in spring because they last through the growing season. In the cooler months, when the fertiliser is fully expended, most plants are not actively growing and so need little additional fertiliser. Follow the instructions on the package. Note: Slow release fertilisers are contained inside little round balls (known as prills). When these balls release their fertiliser they may remain as a shell on the soil surface and will crumble if touched. Although the outer skin remains all the fertiliser will have been used up and should be renewed.
It is a good idea to fertilise pot plants with Nitrosol (liquid food) as well as using a slow release. This gives the plants a quick boost before the slow release fertiliser becomes active. Nitrosol is a liquid form of blood and bone which was developed in Australia. About one capful of Nitrosol to the average watering can will be sufficient. The slow release fertiliser will begin to take effect about two to three weeks later.
Orchids respond well to fertiliser applied at the right time. Many growers swear by Campbell’s Orchid Fertiliser. This product comes in two forms, one tailored to encourage flowering and the other for growth. Each tub is clearly marked. Orchids can also be fertilised with a gentle liquid food such as Nitrosol or with Dynamic Lifter.
For more about fertilisers and soil consult Gardening Down-under by Kevin Handreck (CSIRO Australia, 1993).