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Root inspection

One of the most important, yet often neglected, aspects of tomato growing is the inspection of the roots of soil-grown plants. What comes out of the ground determines where and how next year’s tomato crop will be grown, for there is nothing more dismaying than seeing a crop fail mid-season for the second or third time for want of an end-of-season root examination.

Step 1
When it is time to remove the plants, cut the stems down to about 30cm (12in) above ground level, then remove the plants and every other trace of plant material from the greenhouse.

Step 2
Select a typical stem, take a fork and gently ease the tomato roots from the soil, shaking off any loose soil. What do you see? Are you looking at a mass of fibrous roots of a light brown or pale straw colour with a fair proportion of new roots? If so the soil is healthy enough for another crop of tomatoes in it next year.

Step 3
Tomato varieties vary in their root formation some have long tap roots that go deep into the subsoil, others have a tap and long lateral roots with root hairs spread out along them. When such a root system is lifted it is inevitable that some of the tap or lateral roots will break off. Are they basically healthy looking? If so, the soil is also healthy.

Root diseases
There are several fungal diseases that attack tomato roots but one that is often found in old greenhouse soils is corky root disease. Once infected with Pyrenochaeta lycopersici the roots develop a layer of blackened cork cells which slow or stop the uptake of water and nutrients.The northern European strain of corky root becomes active in diseased soils at a temperature of 15-20C (59- 68F).As the disease spreads along the roots the affected plant slows or stops growing from mid-season onwards depending on variety and weather conditions.

Treatment
If the roots that you carefully dig up are black and cork-covered, try to remove and burn as many of the roots as possible. As for next year, deep and thorough re-soiling may be only partially effective as the fungus spores can survive deep in the soil for many years until they are ‘woken up’ by the presence of growing tomato roots. There are a few resistant varieties available but grafting a susceptible favourite variety onto a multi-disease resistant rootstock is a better option. As a last resort, with badly diseased soils it may be necessary to abandon soil growing in favour of pots or containers of ‘clean’ compost.

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