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Q&A - Question & Answer about gardening

Q: I have a rhododendron. All the leaves have brown spots on them. What is it and what is the cure?

Rhododendrons often suffer from leaf spots. These are caused by a fungal disease and are sometimes made worse by less than perfect growing conditions. Spray immediately with a fungicide, and repeat fortnightly throughout the growing season. You will not eliminate the spots already affecting the plant, but new leaves should be clear of the problem. Make sure it is growing in acid soil in partial shade. If your soil is limey and your rhododendron is of a manageable size, dig it up and grow it in a large pot in ericaceous compost. Remember to water regularly with rainwater or other soft water. Applying an ericaceous plant tonic according to the manufacturer’s instructions should give it a boost.

Q: I am growing tomatoes from seed, they have 6 leaves just the bottom ones look to be dying, is this too much sun/too much water?

I doubt if it is too much sun at this time of the year, and too much water is more likely to cause the plants to rot off at the bottom. In fact, there might not be a problem at all, as the first leaves produced by tomato plants usually die off anyway as the plants mature. Provide good light at the moment, a temperature no less than 15-17°C, and water carefully, and you should soon start to see the first trusses forming. If you find there is a lot of stem between each set of leaves, give better light and space further apart.  

Q: I have a red ant problem; no matter where I dig there are red ants?? What can I do to get rid of the problem?

Ants – either red or black – will not damage your plants but can disturb light soil and the roots of any small plants growing near the nests.    Most domestic plant insecticides will kill ants, but a better solution is to attract plenty of birds into the garden as many species will relish them as a change in diet.

Q: There is a Laburnum tree in my garden and I have been told it is poisonous for human consumption but is this also the case for my dog?

Laburnum is quite poisonous to humans – not deadly but enough to cause a nasty tummy upset.  The main toxin is an alkaloid called cytisene, which causes vomiting and diarrhoea.   If your dog decides to eat any part of the tree, including the twigs, it will experience the same reaction; small dogs and those eating a large quantity have been known to die from respiratory failure.   If you know your dog is prone to chewing plants, it may be better to fence the tree off so it cannot get at it.

Q: My garden is NW facing and overshadowed by mature Oak and Ash. I do everything I can to encourage wildlife but I want to grow more insect-friendly plants for butterflies etc – any suggestions?

This can be difficult as your garden is not in the best position for growing nectar-producing flowering plants, and these are the best for attracting beneficial insects and butterflies.   Early flowering shrubs, like flowering currant (ribes), viburnum and forsythia will bloom before the shade gets too dense and so will attract early insects, and if you have any area that receives a good amount of sun sometime during the day, you could plant flowering herbs like catmint, oregano, lavender and thyme in pots, move them into the shadier parts of the garden for a few weeks, then move them back to the sunny spot before they get too stressed.   Buddleja is the butterflies’ favourite shrub, but it does need a few hours’ sun during the day, otherwise it is short-lived and produces fewer flowers.   You could try growing this in a container, too, moving it round during the summer to the lightest spots you can find.   Many garden butterflies breed on nettle plants – these can also be grown in pots and you will be helping to increase the local butterfly population by doing so.

Q: Can you grow blackberry bushes in tubs?

You can grow virtually any fruit tree or bush in a tub.   Use one at least 45cm in diameter and depth and John Innes No 3 soil-based compost.   Place in a sunny spot and, in the case of climbing fruit such as the blackberry, provide a support such as a large trellis or a fence with horizontal wires attached to it at 30-40cm spacings.   Keep adequately watered throughout the growing and fruit-producing season, adding liquid plant food fortnightly from mid-spring to late summer.   Prune a container-grown blackberry in the same way as if planted in the open ground, removing fruiting canes in late autumn and tying the new ones into the trellis or wires as they are produced.

Q: Can i cut my Laburnum bush right down? It always grows thin & uneven & looks horrible after the flowers have fallen. It’s very old.

It sounds as though this has had its day.   Laburnum is not long-lived, and with age will produce fewer flowers and an untidy shape with a lot of dead material in it.   If you are really fond of it, you could try cutting it off almost at ground level; if there is some life in it, it will send up new shoots that will eventually flower, but a really old laburnum will probably not regrow after such drastic treatment.   This may be the ideal time to remove the old one and replace (nearby, but not in the same place) with a new, young tree.   For fun, try x laburnocytisus adamii, a cross between laburnum and broom, which will produce flowers that are either yellow or pink, or both, and shaped like those of the laburnum or more like those of broom.   It will certainly cause comment among your gardening friends!


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