Replant Problems Dear Gardeners, Message from Jonathan, Have you ever experienced problems with some trees and shrubs that were planted into soil in which the same species was previously growing, and which then failed to do well, or perhaps even died? This commonly occurs with roses – in fact with members of the rose family (Roseaceae) generally – roses, apples, cherries, pears, plums and citrus. Perhaps, for some reason, you needed to replace a rose – the previous one died or you simply decided to replace it with a different variety. But the replacement plant never seemed to “take off.” It seemed stunted and the growth generally was poor. This problem isnt as uncommon as you might think. It is known by several names, including “replant disease”, “soil sickness”, or “rose sickness.” The problem is not limited to roseaceae. The plant will often recover if moved to fresh soil. There is thought to be more than one cause, but the general opinion is that during the life of the first planting, there is a significant build-up of root pests and diseases, such as nematodes (eel-worm) and pathogenic (disease-causing) fungi. These increase gradually and don’t reach high levels until the plants are well established, by which time the root systems are large and robust enough to withstand any adverse effects. The pathogens therefore have no effect on the vigor of the initial planting. However, when the original plant is removed, a high population of these harmful organisms will remain in the soil in the root zone. Then along comes you with a new young plant to replace the previous one. When new young replants with only small root systems are planted in this “contaminated” soil, they struggle to cope. Dealing with the problem isnt as straightforward as one might hope. It used to be thought that the problem was host specific – roses should not be followed by roses, etc. - but it is now suspected that the problem may be more general; e.g. occasionally even non-related species may be affected. The problem doesn’t always occur, however, and in view of this, only rather general advice can be offered. The effects are reported to persist in the soil for between four and twenty years, so waiting for the problem to subside before replanting is not usually an option. Wherever possible, avoid planting a young replant within the root zone of the previous plant. There are no chemical sterilants available to the home gardener. With roses, at least, if you boost the soil fertility with extra fertiliser and compost, you’ll also be boosting root growth and this will reduce the severity of the problem. Changing soil is probably the safest option if you only have a few plants to replant. Basil If you grow basil in your vegetable garden – which you should – you’ll likely soon be picking a few leaves, and perhaps after doing so your plant will turn black and die! I hope it doesn’t, but here’s how to guard against that happening: When picking your basil, don’t just grab a handful of leaves. Instead, use scissors to cut out whole sections of the plant. Cut back to a pair of leaves lower down the stem. This will promote the formation of axillary buds which, in turn, become the next generation of leaves for you to eat in a week or two. If you just snip off the tips you will be left with an ugly stump and mold is more likely to strike. A carefully layered haircut is needed rather than a simple straight swipe. The basil with the most intense aromatic flavor is the common-or-garden sweet Genovese basil. It still reigns supreme for salads. Freshly picked sliced tomatoes, with mozzarella, topped with plenty of raw basil and a dressing of olive oil and balsamic vinegar…. Then there’s Greek (or bush basil – of course the Greeks grow it just to smell the leaves, not actually to eat it!). This is a small-leaved variety that can be carefully pruned once or twice a week, and it is particularly well suited to being containerized. The last basil that’s worth a mention is lemon basil. It makes a delicious herbal tea if you steep a handful of leaves in boiling water for five minutes. By next month, November, your tomato plants should be setting fruit. If the fruit fails to set, spray the the plants with water or shake them vigorously when the sun is on them. This will send the pollen flying and fertilize flowers on which it falls. Rose beetles will make an appearance soon. When they do drench (with a watering can) the soil beneath the plants with KARBASPRAY and spray the bushes as well. Use 10g per 10 litres of water. The onset of summer thunderstorms will encourage powdery mildew on pumpkins, marrows, gem squashes and cucumbers. Spray with MANCOZEB 20g/10litres. If you don’t have space for potatoes but would like to grow them, why not plant them into 20 litres bags? As they grow, add soil till eventually the bag is full. Tip them out in January and harvest the crop. Next time I’ll describe how to plant potatoes in containers.
Posted on: Wed, 08 Oct 2014 11:21:13 +0000
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