VAL BOURNE says now is the time of the season to get mulching

A month ago I was at Royal Horticultural Society garden at Wisley in Surrey and an army of gardeners, probably 40 in number, were mulching the herbaceous borders and roses with the most friable well-rotted manure I have ever seen.

Some were on tractors, some had barrows, some were spreading while others were tweaking the crumbly mix away from newly emerging foliage. Before my very eyes the garden changed into a spruce and tidy affair, as you can hopefully see from the picture.

I drove back feeling depressed about my plot, only to find that a load of muck, which had been ordered some months before, had arrived and been spread over the fruit cage by the better half - as if by magic. For now is the season to mulch, preferably with a nourishing layer of well-rotted muck if you can get it.

A thick mulch will also smother weeds and keep moisture in if applied to damp soil. If the mulch is friable and bulky it will also improve soil structure as the worms drag it down.

Garden compost improves soil structure as well when dug in. But I wouldn't recommend it as a surface mulch. Most garden heaps just don't get hot enough to kill off seeds and you will almost certainly get a sprinkling of germinating weeds and also many self-seeding plants, like foxgloves, malvas and hollyhocks, where you don't want them. Garden compost, lovely though it is, is better used in trenches under beans or other plants.

If you are unable to get muck there are powdered and pelleted forms of chicken manure that are light to handle. They can be sprinkled around plants, preferably on damp spring days, and plants will benefit although they do not improve soil structure.

You can also use blood, fish and bone and seaweed extract to boost growth. All have the three main nutrients in varying degrees - nitrogen (N) for leafy growth, potassium (K) or potash for flower and phosphorus (P) for root growth. They will also contain trace elements.

You can use some other mulches in the garden. But some rob the soil of nutrients as they decompose. Chipped bark or wood chippings look very good with woodland planting like ferns, bulbs and spring flowers, although the blackbirds do redistribute it. However, bark decomposes in situ and uses up valuable nitrogen as it does it. So always add fertiliser before you use bark to compensate. Grass clippings are also a useful mulch, but as they rot down they produce nitrogen in abundance.

If you lay them on a plastic sheet for a day or so, they will turn brown and partly decompose. Then they can be spread under shrubs, or used under raspberries without the sward of green jarring the eye.

I also rate gravel as a mulch among sun-loving sculptural plants like eryngiums, agaves and phormiums. It improves drainage in winter and conserves moisture in summer and if you are wanting to grow agapanthus, dieramas or slightly tender salvias they are much more likely to come through winter. You don't need a membrane, just apply a thick layer straight on to the ground and replace it every third year.

Support Cogges Farm Museum at Witney. I am speaking at the museum in Witney on Sunday at 3pm on growing vegetables organically. Admission is £6 and all proceeds go to Cogges.

Waterperry Gardens near Wheatley are open for the National Garden Scheme on Sunday from 10am to 5pm. For details visit www.waterperrygardens.co.uk