One of the joys of tomato growing is the wide range of varieties that are now available. Each new gardening year brings the latest varieties – several with improved disease bred into their genetic make-up. Thanks to Garden Organic and their Heritage Seed Library, old varieties of tomato are available for members to grow as well as maintaining their genetic gene pool. There are some lovely flavours to be found among the heritage varieties.
But, and it is becoming a very real ‘But’, in the past many varieties lost favour because of their lack of disease resistance. In fact, the biggest threat to commercial tomato growers in Lancashire in the mid 1950’s was tomato leaf mould (Cladosporium fulvum) which has several strains 1-5 or a-e plus any new mutant strains. The plants in whole greenhouses would turn mottled yellow then brown during warm wet weather. At times during the summer of 2021 we had several days off wet warm ‘fungus weather’ when leaf mould attacked susceptible crops. Was the weather pattern of 2021 a foretaste of the future? Are many of the old varieties in jeopardy?
As there are no organic answers to leaf mould, if it or Grey mould (botrytis cinerea) appeared amongst your plants last summer they will have left countless spores all over your greenhouse. If not already done, now is the time to thoroughly clean the greenhouse. After removing the contents, I have found that hot soapy water (soap, not detergent) and a scrubbing brush applied to the greenhouse structures and fittings together with equipment to be effective. The glass is easier to clean with a foam sponge. The outside glass is easier to reach with a long handled flat foam sponge which will reach up to the ridge. Again warm water with liquid soap appears to keep glass cleaner for longer than when detergent is used. In the past in the Aire Valley when the mill chimneys emitted their thick smoke, greenhouses wore a winter overcoat of soot. The soot went out when the clean air act came in, only to be replaced in some areas close to busy roads by an insidious film of traffic haze. Wiping the glass with a piece of clean moist rag will reveal the amount of light inducing haze that might be in your area. The dirtier the glass, the stronger the light values have to be before photosynthesis, the very reason we are using a greenhouse, can begin.
During the summer of 2021 many gardeners experienced the worst attack of potato/late blight they had ever known. Whole beds of fruiting tomato plants were wiped out, a season work gone in a few days of what is known as a ‘Smith period”, that is when 2 consecutive days when the temperature does not fall below 10’C combined with 90+% of humidity for at least 11 hours a day. Whilst there are no practical organic answers to blight there are tomato varieties with various levels of resistance. If blight is to become an annual event, it is worth trying some of these varieties. Last year I grew some Mountain Magic, which not only provided delicious fruit but only had the odd leaflet touched by blight which were plucked off and the plants continued to grow. Ironically with ripening fruit on the 14th and 15th trusses, a sudden severe night frost got into my cold greenhouse and killed the plants. Now there are several more blight resistant varieties to choose from I shall grow more of them in 2022.
With fuel costs set to rise, next month we will have a look at economical tomato plant propagation.