Gardeners now have two main ways of controlling weeds -physical and chemical. PHYSICAL METHODS OF WEED CONTROL Physical methods of weed control include hand pulling of weeds, soil cultivation or tillage and mulching. These methods have been used for centuries and many of our present-day garden practices, such as the spacing of vegetable crops, are dictated by the need for soil cultivation. HAND PULLING AND HOEING Hand pulling is probably the oldest method of controlling weeds. In spite of many revolutionary discoveries and the introduction of new practices this method still survives. Hand pulling can be very effective especially against weeds such as groundsel (Senecio vulgaris) and sun spurge (Euphorbia helioscopia) that can be uprooted easily, but it is almost useless against perennials. It is often the only appropriate method for rock gardens containing a large number of valuable alpine plants. Hand pulling is not very practical as the sole method of weed control in a large area but is useful for dealing with the few resistant weeds which often survive a herbicide treatment. Hoeing can be done more rapidly than hand pulling and is very effective against many annual and biennial weeds. It is less satisfactory against perennials unless hoeing is repeated at appropriate intervals to deplete the food reserves in their roots. A knowledge of the growth habit of weeds can help greatly in the choice of a suitable method of control. Although cleavers (Galium aparine) is a very troublesome weed when its straggling shoots have become entwined with cultivated plants, it can be killed easily by hand breaking the thin stem at ground level. It is not necessary to remove the root system. In contrast the well developed tap root of many weeds such as dandelion (Taraxacum officinale) must be removed to achieve control. If the root is not dug out the weed will regenerate from adventitious buds on the lower part of the root. Not all weeds with tap roots will regenerate in this way. Hogweed (Heracleum sphondylium) is only capable of resprouting from basal buds within 3in(8cm) or so of the soil surface. If the rootstock is severed below this depth no regrowth will occur. MULCHING Mulching is an old method of weed control that has been revitalised with the availability of more convenient materials. Mulching controls weeds by excluding light and preventing plants from photosynth-esising. In the past many types of organic mulches have been used such as leaves, sawdust and peat. Such mulches control weeds that germinate near the surface, but they are ineffective against perennials with vigorous shoots such as couch grass (Agropyron repens). Much better control of perennial weeds can now be achieved with black polythene. This type of mulch will suppress all weeds for several years as long as the polythene remains intact. It is most useful in the fruit garden or around trees or shrubs. It is also very effective around cuttings that can be rooted in their final position.