The secret to a happy garden? Great soil. Here’s how to improve yours…
To most people, soil is just dirt. But to plants, it’s life or death. Whether you garden on clay, sand or chalk, it affects what will grow well. And unless you’re lucky and have naturally good ground, it’s likely yours will need improving.
Loam, dark brown soil which contains a good mix of everything – clay, sand and organic matter – is generally regarded as the best garden soil, and traditional soil improvement techniques are designed to turn whatever soil you inherit into something as much like loam as possible. You don’t have to take that route though – if your soil is particularly extreme, it can often be easier to design a garden that uses plants that are at home in such conditions.
What’s in your soil?
You can discover a lot by looking at the garden after it’s rained, and by rubbing a handful of soil between your fingers. Sandy or gravelly soil feels gritty and won’t hold together. Clay soil feels smooth, can be rolled into a sausage shape, and turns to sticky mud after rain. Chalky soil is pale, often with visible white lumps; peaty soil is almost black when moist and crumbles between the fingers; loamy soil – everyone’s dream – holds moisture well, but allows it to drain away after heavy rain.
Improve what you have
There are two ways of improving the soil – one is by digging in organic matter, such as compost, to improve the structure and add nutrients; the other is by adding fertilisers. Actually, you need both, because they each have a different job to do.
Organic matter is ‘roughage’ – it improves the soil’s structure and releases nutrients. The cheapest form is compost – you can make it yourself with a compost heap, and it costs nothing. You can also use manure, which is also often given away free by horse owners; or buy mushroom compost, composted bark or spent hops at garden centres.
Sandy, chalky or gravelly soils are fast-draining and ‘hungry’, so you can improve them by digging in organic matter in spring and autumn, mulching (piling it on top of the soil) where you can’t dig. Clay soil turns to good fertile earth if you dig in or mulch with organic matter and add grit (from garden centres). Peaty soils are short of nutrients, so organic matter will add ‘body’, while even good loamy soil needs occasional helpings to keep it in good condition.
You need to use fertiliser as well. It comes in two types: organic, from natural sources, and chemical feeds. Organic fertilisers have the advantage as they keep soil bacteria busy – and busy bacteria are happy bacteria. Fertilisers contain different amounts of three main elements: nitrogen for promoting leafy growth; phosphorus to help roots, and potassium, which is vital for producing flowers and fruit. A general purpose fertiliser such as Growmore (inorganic) or blood, fish and bone (organic) is good for preparing soil before planting or sowing, and feeding all round the garden. The three main ingredients are present in equal quantities, making it a ‘balanced’ fertiliser – the plants’ answer to a good square meal.
My standard soil improvement technique is to dig in manure or home-made compost on new beds and mulch the soil surface on established beds, in winter and spring. I also fork in a good sprinkling of organic fertiliser just before sowing or planting.
A final reason to get digging? Air flows more freely when soil particles are looser; surplus water can run away, and it’s easier for roots to penetrate, meaning plants grow better.
The acid test
Gardeners talk a lot about the pH of their soil – that is, how acidic or alkaline it is. You can buy testing kits from garden centres. If the pH is 7, you have neutral soil, which means most plants will grow happily. Soils with a higher pH are more alkaline, while soils with a lower pH are more acidic. Most garden soils are in the pH range 6-8. If you have extremely acidic or alkaline soil, certain nutrients will be unavailable to plants and you may have problems. It’s difficult to make drastic changes to the pH. You might alter a small patch perhaps, but for a whole garden… forget it. If you pine to grow acid-loving rhododendrons when you’re saddled with chalky soil, grow them in containers using lime-free compost instead. You’ll enjoy your garden much more if you don’t turn it into a battle ground.
No cook wants to be without herbs and no gardener wants to be without them for fragrance. They have the advantage that many of them are perennial, they can be squeezed into pockets on the patio and a little goes a long way.
Herbs are some of the very easiest edible crops to look after. Mediterranean-style herbs such as bay, rosemary, thyme and sage must have a warm, sunny spot with well-drained soil; and basil is very fussy about warmth and shelter, but it doesn’t like hot, searing sun – it’s best grown in pots of potting compost in semi-shade. Other herbs, such as tarragon, parsley, sorrel and mint are happiest in normal garden conditions in sun or light shade with soil that holds moisture but where they won’t have wet feet.
Plant perennial herbs (such as chives, mint and fennel) in spring and frost-tender herbs (like lemongrass) in summer, after the last frost, so you have the longest season in which to use them.
Remove flowers from leafy herbs like basil and chervil to keep them going longer, also from coriander and dill. But there’s no need to bother taking flowers off perennials.
Water lightly when the soil dries out, and use a general-purpose liquid feed regularly every two to three weeks for herbs in containers. Only big loutish perennial herbs like mint need lots of water and heavy feeding; when you grow mint in pots you can hardly be too generous.
From plot to plate: How to preserve your herbs
Herbs are available in large quantities in the summer, and if you want to preserve some to use in winter, the time to do it is before they start flowering, otherwise the leaves lose a lot of their flavour and the stems become tough and woody. Cut clean, healthy sprigs and rinse in cold water to dislodge dust and insects.
- To make herb-flavoured oils, place a few good-looking sprigs of herbs in a jar of good olive oil and leave for a few weeks in a cool cupboard.
- To dry herbs, hang small bunches up in a warm, airy place out of sunlight, or pop them on a baking tray for half an hour in a warm oven. Crumble them on to a sheet of paper, pick out the twiggy bits, and store the dry, leafy herbs in clean, dry glass jars out of sunlight. That way, they’ll stay green instead of fading to an unappetising shade of khaki.
- To freeze herbs, chop up finely and put a teaspoonful of each into the squares of an ice cube tray. Top up with water and put in the freezer. Once frozen, you can tip out the herb-cubes into labelled plastic bags.
- To make mint jelly, use an apple jelly recipe but add lots of chopped mint. Try using eau de cologne mint instead of the usual garden mint; it smells as good as it tastes. You can adapt the recipe to make other herb jellies too – sage and thyme jelly both go well with pork and lamb.
Your spring checklist
The gardening season starts here! The days become longer, the ground is warming up and the weeds are starting to grow. Stay on top now and the rest of the year will run like clockwork. Here’s a handy list of the main tasks and when to do them.
Early spring: March
Spring clean borders and fork over vegetable beds. Hand weed or hoe and mulch with organic matter.
- Pressure-wash drives and patios and remove weeds and moss.
- Prune roses and standard apple and pear trees.
- Cut the lawn for the first time and begin regular mowing. Lay turf before the end of the month if you didn’t in autumn.
- Sow wild flowers, hardy annuals and herbs.
- Plant roses and climbers, pot-grown shrubs and fruit trees; plant and divide perennials.
- Sow lettuce, rocket, radishes, spring onions, leeks, onions, broad beans, parsnips, spinach, turnips, early varieties of carrots and peas.
- In the greenhouse, sow tomatoes, chillies, sweet peppers, half-hardy annuals and bedding plants; pot up new plug plants and tubers of begonia, arum lilies and dahlia; and plant, water and hand-pollinate strawberries.
- Keep on top of weeding.
- Feed roses, borders, hedges, trees, shrubs and spring bulbs with fertiliser.
- Feed grass, remove weeds and rake out moss and re-seed bare patches in your lawn. Mow at least once a fortnight.
- Prune winter jasmine and hydrangeas; tie back shoots of climbing roses, wall-trained shrubs and new climbers.
- Plant roses, trees, shrubs and perennials.
- Sow summer cabbage, brussels sprouts, early peas, beetroot, lettuce, carrots, and hardy herbs such as parsley, coriander, fennel and dill.
- Water and hoe vegetables regularly.
- Thin out and transplant seedlings.
- Ventilate the greenhouse on sunny days but shut it down mid-afternoon to keep heat at night. Buy and pot up plug plants and prick out tomato seedlings into individual pots.
- Plant up outdoor tubs and hanging baskets but keep them under glass.
Late spring: May
- Clip hedges and prune spring-flowering shrubs.
- After the last frost, plant half-hardy bedding plants, dahlias and tender exotic plants.
- Mow lawns weekly, removing weeds.
- Support perennials with small stakes or poles.
- Deadhead spring-flowering bulbs and prepare the ground for replanting.
- Plant tubs, windowboxes and hanging baskets in the middle of this month, but don’t hurry as they’re killed by cold.
- Water fruit bushes and the vegetable patch regularly. Sow swede, carrots, autumn cabbage, cauliflowers and peas; and french and runner beans, sweetcorn, courgettes, squashes and pumpkins after the last frost.
- In the greenhouse, ventilate by day and water more frequently. Continue to prick out and pot on seedlings, cuttings and young plants.
- Watch out for late frosts – protect new shoots and fruit tree blossom with horticultural fleece.
Alan’s book Grow Your Own Fruit and Veg will be republished on 4 March by BBC Books, price £18.99. To order a copy for £16.14 before 27 March go to mailshop.co.uk/books or call 020 3308 9193. Free UK delivery on orders over £20.