Hi Sibe,

I have about 3in (76mm) of top soil in my garden, can you tell me if I can use compost to build up the levels of borders or is soil best.

Thanks

Our gardening expert replies

Hello!

Unfortunately, you didn't say what was below the top-soil. If this is rubble and stone you have a much different problem than if it were, say, heavy clay.

The best way of improving topsoil is to dig in large quantities of organic matter: well-rotted manure or preferably your own home-made garden compost. This will gradually become incorporated into the sub-soil and will increase the depth of top-soil (the presence of organic matter is the main difference between top and sub-soil).

If by 'compost' you mean bags of compost, bought from garden centres, this would not be a good idea. These mainly consist of either peat, composted bark or coir and - particularly peat - do not make good border soil. The problem is that these materials do not have much ability to hold plant foods so that you would, in effect be making an extremely poor soil. Loam is the basis of a good soil as this can, by its chemical structure, preserve and supply plant nutrients as and when plants need them.

A load of good quality top-soil is by far the better option. Top-soil comes in different qualities, however, so you need to be quite careful what you purchase. The ideal top-soil is a friable weed and stone free mix that has not been stacked in huge piles. These squeeze out oxygen and kill essential soil bacteria which keep the soil healthy. If possible you should act on personal recommendation before ordering the top-soil, or maybe go along and take a look at it before you buy - it's rather difficult to put right if you have a bad load delivered!

All the best

Sibe