Gardening – Feeding frenzy

If you haven’t already, now is a good time to break out the fertilisers. Plants can struggle on for weeks, months or even years without fertiliser, but just like water stress, poor nutrition leads to reduced growth and increased susceptibility to disease.

It is important to understand the properties of each fertiliser, its nutrient content and how it works. I use a wide variety of fertilisers in my garden, with the choice of what type of fertiliser, timing of application and amount to apply being dependent on the particular crop being fertilised. I’ll give you a few examples to highlight some of the principles of plant nutrition.

I feed my bromeliads in early summer by dropping a few pellets of sheep manure into each cup.

Coupled with the occasional spray with foliar seaweed, this is enough to keep these plants growing well and showing off their best colour. Too much fertiliser will result in bromeliads that are too green, while strong chemical fertilisers may cause burning of the central leaves.

At the other end of the feeding spectrum, bananas need lots of fertiliser to produce well. If left to their own devices, they will produce skimpy bunches of a dozen or two small bananas, but if well fed, a good bunch can have up to 200 fat bananas! I give them plentiful leaf litter, compost, sheep pellets, sulphate of potash and handfuls of balanced fertiliser like Nitrophoska throughout the growing season, from early summer to mid-autumn, about once per month.

Tomatoes are another heavy feeder. They get a base dressing of my favourite combination of four handfuls of blood and bone, two handfuls of granular sulphate of potash, one handful each of dolomite and gypsum on a five square metre bed. Then, as the plants grow, they get a big handful of sheep pellets around the base of each plant, with a tablespoon of Nitrophoska each once the fifth truss has formed, as this is when the plants nutrient needs are at their greatest. Other big feeders such as eggplants, capsicum, pumpkin and melons get similar treatment, with quantities and timing adjusted to suit their growth habits.

I often follow up heavy feeders such as these with a less hungry crop such as carrots, radishes, beetroot. If overfed, these will produce lots of top growth and gnarled, twisted and cracked roots, so I rely on the residual fertiliser from the last crop and only feed a little if they are looking a bit peaky. On the other hand, leafy greens such as spinach, lettuce and silverbeet need plentiful nitrogen to produce big, succulent leaves and grown too lean will produce bitter, smaller leaves.

Some plants need a more acid soil environment, including blueberries, gardenias, rhododendrons, camellias and hydrangeas. Of course no lime or dolomite should be applied around these plants, but gypsum can be useful to provide some calcium without raising the pH. Special acidic fertilisers can be purchased for these crops, and this is the solution I use, rather than making my own.

Other crops have a high need for a specific nutrient, such as magnesium. Citrus are a good example of this, which is why I’ll sprinkle a little Epsom salts (magnesium sulphate) or dolomite (which has magnesium carbonate as well as calcium carbonate) around the drip line in late spring or early summer.

Root crops such as carrots, potatoes and kumara need lots of phosphorus, as do peas and beans, so look for fertilisers that are high in this element for these crops.

This is just a brief introduction to the nutrient requirements of plants. It is a subject that has many layers and it’s well worth digging into (excuse the pun), for each crop you grow to make sure you are getting the best results.