Fertilising native plants
Most native plants will grow adequately if planted on a suitable site but early growth rates can be increased by the addition of an appropriate type and amount of fertiliser. The fertiliser enriches the soil and ensures that plants have the necessary supply of nutrients as well as the major nutrients - nitrogen, phosphorus, potassium, calcium, magnesium and sulphur.
Trees also require trace elements such as iron, copper and zinc. The type and quantity of fertiliser used depends on soil types and conditions, and the species being planted.
Placement of fertiliser
Seedlings and young trees
Fertilisers can be spread in a ring around the tree if the area is relatively flat, but should otherwise be in a band on the uphill side of the tree. An alternative method i to dig one or two small holes 10-20 cm deep near the tree, place the fertiliser in the hole and refill with soil. Fertiliser should be 20-50 cm away from the base of the tree.
Advanced or mature trees
Healthy mature trees show little response when general fertilisers are applied, but particular elements may be applied to correct deficiencies. Sick or damaged trees may also benefit from fertiliser application. Spread the fertiliser evenly or place it in holes (e.g. made with a crowbar) across the area beneath the canopy. Organic fertilisers such as blood and bone and composted poultry manure vary in nutrient content but are usually good sources of phosphorus and nitrogen. Other organic substances such as old cow manure, hay, sawdust, newspapers, grass clippings and bagasse are not fertilisers.
In some cases these materials may even reduce nutrients available to young trees as they tie up nutrients in the composting process, only releasing them to the tree after composting has finished.
Native plants can be broadly categorised according to their natural habitat. Below is a general guide to the fertiliser requirements of trees from each category.
1. Rainforest from fertile soils
Rainforest trees are generally broad-leaved species which require high water and nutrient conditions. These species often demand nitrogen, particularly when grown in full sunlight (e.g. park or garden situations). If grown in the shade, their nitrogen (N) requirements are less. Phosphorus (P) is also necessary, so use of complete fertilisers is necessary for these species on poor soils.
2. Eucalypt forest from moderately fertile soils
Eucalypt forest includes wet sclerophyll types with species such as flooded gum, tallowwood etc, and broad leaved understorey species allied to rainforest elements. These are generally nitrogen demanders, but not to the same extent as the rainforest species. They will also respond to P provided N levels are adequate. Again, moderate applications of a complete fertiliser is recommended.
3. Eucalypt forest from poorer soils
These are generally dry sclerophyll forest trees with understoreys of sclerophyllous species. Nutrient requirements of mature specimens are probably adequately catered for in most soils, but seedlings will respond to balanced fertilisng with N and P on all but the best soils.
4. Heath and Wallum
Species on poor soils, often poorly drained These communities have minimal fertiliser requirements and do not need fertilising under most conditions. They generally respond well to mulching (e.g. pine bark) and a very small starter dose of low NP fertiliser.
5. Arid Zone Species
These come from variable soils, and good drainage takes precedence over nutrition in a horticultural situation. They often are adapted to alkaline soils so that careful liming can be helpful. Most are generally adapted to soils of poor fertility so treat as heath plants or dry sclerophyll plants depending on their origin.
6. Strand Plants - from dune areas, behind dunes and behind mangrove situations
These plants have adapted to salt spray/drift and periodic soil salinity. Soil alkalinity/acidity can be variable, though generally they prefer acid conditions. They will respond to N and P and some spray. Treat similarly to the dry sclerophyll species, but investigate any possible lime requirements. Fertiliser rates Rates of fertilising necessary will vary widely depending on the species being planted and soil types and conditions. Rates of between 50 and 300g at planting are common, followed by similar amounts after good rain in the spring or early summer. Another follow-up application the following spring may also be beneficial.
TYPES OF FERTILISERS