Q How much fertiliser do I need to use?
A You can approach this question in two different ways. The first is, how much do I need to use to produce the best crop? The second is, how little can I get away with? On environmental grounds, we suggest the latter.
Most garden soils contain plenty of nutrients and organic matter, compared with agricultural land. The quantities suggested in the table overleaf are based on the total amount of fertiliser needed to see each vegetable through to harvest.
If your soil is reasonably fertile, you can halve this amount. If you add reasonable amounts of garden compost or well-rotted manure each year, you can reduce the amount of fertiliser that you apply even further.
Organic gardeners would argue that once your soil is in good condition, you shouldn’t need to add concentrated fertilisers. As a halfway house, substitute organic fertilisers for the Growmore if you plan to grow organically. Of course your crops need nutrients and water to produce a good yield, but they may not need as much of either as you'd think.
Caption: Veg that are near harvest need water in dry weather
Q Which type of fertiliser should I use?
A For many gardens, it's best to use a balanced fertiliser – one with equal amounts of the three major plant nutrients: nitrogen (N), phosphate (P) and potash (K) – such as Growmore. But P and K are retained within soil, so, if there’s sufficient in yours already, why add more? To find out, consider sending a sample of soil to be tested.
If there’s plenty of P and K, you need only top up with N each season. Use a nitrogen fertiliser, such as sulphate of ammonia or nitrochalk (best on acid soils since it contains lime), for leafy crops.
Apply about half the total amount of fertiliser, worked into the soil, before you sow or transplant veg. Apply the second half when the crop is about halfway to maturity.
Q Can I use manure or compost to feed my vegetables?
A Well-rotted farmyard or stable manure and well-made garden compost contain useful amounts of plant nutrients. Organic matter also helps to open up clay soils and retain moisture in free-draining, sandy soils.
If supplies are short, use them on the crops that are likely to gain most benefit (see table overleaf). Apply about a bucketful per sq m each year. Remember that each kilo of manure contributes about as much nitrogen as 25g of Growmore. If you apply more and it is not used, it may pollute underground water in exactly the same way as artificial fertiliser.
Caption: Mulching with garden compost will add nutrients to the soil
Q Does crop rotation help to keep plants well fed?
A Aside from any benefits of pest and disease control, moving groups of vegetables around from year to year helps to ensure that nutrients are used efficiently. It also means that manure or compost can be applied to the crops that benefit most in the first year. Any residues will be used up by later crops.
Q How much watering is needed if it's dry when I'm sowing veg?
A If it is dry at sowing time, water the seedbed thoroughly a day or two before sowing. Similarly, if the surface is dry when you plant out, water the pots thoroughly first and water the young plants in well. Thereafter don’t water unless the soil becomes very dry.
To check, dig a hole the depth of a spade: only when the soil this deep starts to feel dry do you need to consider watering.
Ways to save water
1 Construct permanent beds and paths.
2 Direct water to the base of plants.
3 Mulch beds with organic matter in early spring to reduce evaporation.
4 Plant large, widely spaced plants through a plastic mulch.
5 Make a bean trench and fill it with the remains of previous crops, shredded newspaper, manure and such like to retain moisture.
6 Hoe regularly: a dry, loose surface helps prevent evaporation from deep down.
Caption: Hoeing not only kills weeds but helps conserve moisture
Q If there is a dry spell, what’s the best policy?
A If the soil starts to become very dry, don’t waste water. Give small areas a thorough soak every week. If you just wet the surface daily, this will encourage surface roots, which are more drought-susceptible.
Q If water is short, which vegetables need it the most?
A Concentrate on vegetables that will get the most benefit:
- Leafy vegetables and quick-growing salads should receive roughly 11 litres per sq m weekly. Adequate water encourages quick growth which is sweet, crisp and tender.
- Veg near harvest, such as peas and beans after pod set, and sweetcorn when cobs are forming, will benefit from 25 litres per sq m. Lack of water will lessen yield.
- Summer cabbage and cauliflowers, and maincrop potatoes, need just one good soaking a couple of weeks before harvest to boost the edible parts.
- Most root crops and winter vegetables should survive in most years without additional watering.