As soils warm and daylight hours increase, the most urgent gardening task now is to respond to the nutritional needs of our plants, advises PETER CUNDALL
It’s time to spring into action
It happens every spring. As plants emerge from winter they urgently demand fuel. Spring is the crucial time when need for fertilisers is at its highest and if many plants are left unsatisfied, growth and vigour can suffer for the rest of the growing season.
The most urgent gardening task now is to respond to the nutritional needs of our plants as soils warm and daylight hours increase.
Different plants have different needs. There is little point in scattering manure and other fertilisers indiscriminately around. It’s the quick-growing leafy plants that need high-nitrogen fertilisers such as decomposed chook manure or diluted fish emulsion.
In the vegetable garden the greediest plants include lettuce, cabbage, Brussels sprout, silverbeet, Chinese cabbage, oriental mustard, mizuma greens, Pak choi, rhubarb and spinach. All these plants benefit from being grown fast and high-nitrogen fertilisers regularly applied during growth are the main driving force.
Other vegetables that do well in a slightly less enriched soil include celery, leeks and potatoes. Many popular vegetables have a surprisingly-low need for nitrogen-rich fertilisers. They include asparagus, zucchini, cucumber, carrot, parsnip, globe artichoke, kohlrabi, radish, salsify, swede and turnip.
Legumes such as beans and peas can fix their own nitrogen from soil atmosphere. They resent and even react against high-nitrogen fertilisers and manures. Even leaf vegetables such as broccoli and cauliflower can be over-fed and respond by producing masses of leaves and delayed heads or curds.
Over-fertilised carrots and beetroot become ‘all top and no root’ and topple over. Should the soil also contain too much organic matter carrots become too badly-forked to be of much use.
Long-keeping onions and garlic grown in nitrogen-rich soil can be a disaster. They produce bloated bulbs which are soft, fail to keep, have an insipid flavour are prone to fungal diseases and black aphid attack.
In the ornamental garden many attractive flowering shrubs have low nitrogen requirements. They include
Different plants have different needs. There is little point in scattering manure and other fertilisers indiscriminately around
rhododendrons, azaleas, camellias, ericas, pieris, daphne, proteas and cistus. All these plants grow contentedly with one feed a year, preferably as a low-nitrogen sheep or cow manure mulch during spring.
Roses grow happily with an occasional sprinkling of blood and bone with a little potash added while hydrangeas thrive when regularly watered with weak manure water.
Most Australian plants grow contentedly and strongly in relatively hungry soils, often without any added fertilisers. However, most respond if mulched annually with well-rotted animal manures but go very easy with chook droppings.
Stable manure when fresh can be deadly around all plants. Australian plants are especially sensitive. It is far better to pile it in a heap to thoroughly rot down before using.
Native plants from low-rainfall districts are used to slightly-impoverished soils and are best left unfertilised in most home gardens. Some, especially species of banksia, hakea, grevillea, acacia and most eucalypts react badly to even small amounts of superphosphate so avoid using the stuff.
Almost all plants grown in containers are our prisoners. They are totally dependent on us for their survival and also have different fertiliser needs according to species.
Liquid fertilisers are probably the best means of feeding pot-grown plants but they must be heavily-diluted. They should only be applied to potting soil after it has been given a good watering. It also pays to water again afterwards to be doubly safe.
Most vigorous house or tub plants grown for lush, attractive leaves invariably benefit from extra-weak liquid fertilisers applied monthly during spring and summer. Such plants include aphelandra, Begonia Rex and B. grandis, Solenostemon (Coleus), ficus, monstera and philodendron.
On the other hand flowering houseplants, especially orchids and African violets bloom more persistently if fed with diluted, potash-based fertilisers.
Unless in a heated greenhouse, most container plants are not fed during winter in Tasmania
Cacti and other succulents respond well to weak liquid fertilisers containing a balance of nutrients.
A small amount of seaweed concentrate added to compost tea or heavily-diluted liquid manure encourages steady growth.
During winter the potting soil around these plants should be just moist with no fertilisers applied.