Tips on variety of water-retaining mulches to spread on your borderss - plus, find out what else needs doing in the garden this week.

By Hannah Stephenson.

Mulching is such a useful process and so simple. You spread a layer of something or other on top of your soil, around your plants, and it stops the weeds coming up and keeps the existing moisture in.

It also reduces soil temperature, which will therefore reduce water loss, and makes beds and borders look somehow tidier, creating a neat carpet under which to display your plants.

But there are many mulches from which to choose - from organic manures and garden compost to bark chippings, straw and leaf mould. So which one is best?

Well, from a nutritional point of view, you need to go for bio-degradable mulches, those which break down gradually to release nutrients into the soil.

You can't beat a well-rotted farmyard manure, which is rich in nutrients, so it's perfect for hungry feeders such as roses and fruit bushes. Just make sure that it is well rotted because fresh manure releases ammonia which will scorch plants and may kill them. If you find fresh manure at a cheap price, it will need stacking for at least six months to rot down before use.

If you don't want to buy farmyard manure, think about making your own compost, but be warned that you need to follow certain guidelines to make rich, effective compost which is balanced. Don't fill a compost bin with mainly grass clippings or you'll end up with a soggy mess.

Use a mixture of household waste including vegetable peelings, egg shells, torn up newspaper and tea leaves or coffee grounds, along with dead plants, rootballs or used potting compost and autumn leaves. Don't add any cooked foods or meats and avoid perennial weeds and diseased plants, which may leave spores in the compost which will do their damage when you add it to your borders.

Another homemade mulch is leaf mould, made from autumn leaves you rake up, which can then be stored in dustbin liners with holes for drainage. It will take a year to break down but you should end up with a dark, sweet-smelling material which you can add to your beds and borders. However, it tends to be shortlived and you'll probably have to mulch again next season.

The best quality leaf mould is produced from the leaves of oak, beech or hornbeam. Thick leaves such as sycamore, walnut, horse chestnut and sweet chestnut need to be shredded before adding to the pile.

If you're patient, you can use well-rotted leaf mould which is more than two years old as seed-sowing compost, or mixed equally with sharp sand, garden compost and good-quality soil as potting compost.

Other choice mulches include garden compost, spent mushroom compost, cocoa shells, wood chippings, processed conifer bark, straw for strawberries and seaweed.

Bark, a by-product from the timber industry, is available in various forms and colours. Composted bark is better and is widely available in garden centres and doesn't go soggy in really wet weather.

Wood chips, a cheaper option, while effective as a mulch, take nitrogen from the soil and may slow plant growth, so you may have to add a little more nitrogenous fertiliser to the soil if you use them.

'Spent' mushroom compost, referring to the fact it is the compost left over from mushroom farming, is also widely available and as it contains chalk it is useful on acid soils that are low in organic matter, where the liming effect of the chalk is an added benefit to soil fertility.

It's brilliant used in the vegetable garden, but should be avoided where ericaceous plants such as rhododendrons, camellias, azaleas and heathers are being grown, as these plants need acidic growing conditions and are chalk-hating.

Mushroom compost is also not recommended for neutral, alkaline or chalky soils, which would be made excessively alkaline by the addition of further chalk.

And on the subject of peat, without getting into a heated debate on the conservation issue - don't use it to mulch the soil because it dries out, blows around and doesn't contain many nutrients.

BEST OF THE BUNCH - Magnolia They are the absolute stars of spring, their huge cup-shaped white and pink flowers providing a dazzling display and there's none so impressive as the tree, M. grandiflora, which will reach 18m (60ft) in time.

The most popular variety is M. soulangiana, a spreading bush whose goblet-shaped flowers appear in April, white and purple-tinged at the base.

If space is limited, go for the compact, slow-growing deciduous M. stellata, which grows to around 3m (9ft) and hose silky buds open in mid-spring to produce star-shaped, white flowers.

Magnolias like moist but well-drained, humus-rich, acid soil in sun or dappled shade. Many don't like chalk but any reasonable garden soil will do. The soil should be enriched with plenty of organic matter and the plant should be well watered until established.

Good enough to eat... Sowing French beans (Phaseolus vulgaris) They are the ideal veg - delicious to eat, ornamental and floriferous. Start sowing dwarf or climbing varieties indoors in April and they should be cropping throughout the summer.

They are best started off indoors, in two seeds per pot at 5cm (2in) deep, then planted out once they are around 8cm (3in) tall, but you must wait until the last frost has passed as they are extremely susceptible to frost. Plant them in their final places in early June and support them on bamboo cane wigwams or double rows of canes.

Make later sowings directly into the ground in June so you have crops through to October. Train the climbing beans up trellises, over arches or along fences to make the most of their beautiful white or lilac flowers.

Good varieties include the dwarf Purple Teepee, which turns green on cooking, and 'Blue Lake', a climbing type.

Three ways to - Rejuvenate a conifer 1. If it is brown in the centre, remove the small dead branches to reveal the shape of the main branches. Cut off a few of the lower large branches to enable you to underplant with ground cover plants which will withstand dry shade such as vinca and cranesbill geranium.

2. If the conifer is brown at the base, plant variegated ivy at the base which will use the brown, lower branches as a climbing frame.

3. Transform a conifer into a standard by removing all branches up to 1.5m (5ft) or lower and then lightly trim the top to shape.

What to do this week :: Start hardening off bedding plants but put them under cover if frost threatens.

:: Plant hanging basket and keep them in a greenhouse or frost-free conservatory or porch until all danger of frost has passed.

:: Apply a general slow-release fertiliser to containers. If it's applied as a surface dressing in spring, it should last container plants the whole season.

:: Earth up early potatoes to protect them from light and frost.

:: Begin mowing the lawn regularly, to encourage dense growth.

:: Feed fish as they become active again after winter.

:: Start removing sideshoots and pinch out tendrils if growing sweet peas on a cordon system.

:: Remove isolated weeds in paths, drives and patios with an old knife or by spraying with a spot weeder.

:: Give increasing amounts of water to greenhouse plants in containers, which should now be growing.

:: Replace rock plants showing signs of severe frost damage, such as loss of foliage, discoloured leaves and dead patches.

:: Transplant rhododendrons and azaleas that need to be relocated.

:: Apply rose fertiliser and gently hoe in around the plants to promote strong growth.

:: Apply a dressing of dried blood or dry tomato fertiliser to trees or shrubs that need a pick-me-up.

:: Take hardwood cuttings of evergreen shrubs and leaves.