QUESTION: My roses developed quite a lot of disease as the summer progressed. They are now displaying plentiful rust – is it worth doing anything about it at this stage in the season?

ORACLE: Yes it is. Many gardeners leave rust to run riot over their roses late in the season. This often causes damage to stems, and die-back through winter and next season. Regular spraying with Dithane will keep it under control. This fungicide sticks well to stems and foliage and hangs onto the plant if the weather is wet. Cut off any badly affected shoots and leaves, and clean up any fallen leaves from around the plants. If these are left on the soil they will retain the spores around the plants for the following season.

QUESTION: I want to plant some dwarf bulbs around the base of trees in my garden. Some of the trees are in grass, others have ground cover around them. What should I choose?

ORACLE: Dwarf spring flowering bulbs are shown to advantage around the base of trees. Plant between the drip line (the extent of the branches) and the trunk for best results; in this area there is less competition for water and nutrients. Choose subjects that enjoy a semi-shaded situation; sun lovers such as tulips, dwarf iris and crocus are less satisfactory. Snowdrops work well in grass or amongst low ground cover if the situation is reasonably moist. Plant the bulbs as soon as you buy them as they dry out quickly when stored.

Dwarf narcissi are always a good choice. Plant in clumps of 10-15 bulbs spacing them a couple of centimetres apart and three times the depth of the bulb deep. ‘Jack Snipe’, ‘Jetfire’, ‘February Gold’ and ‘Thalia’ are all good. The winter aconite, Eranthis hyemalis has yellow buttercup flowers. Plant this where it does not have competition from grass or other plants. It works well when combined with the autumn flowering Cyclamen hederifolium.

Glory of the snow Chionodoxa luciliae has starry blue, whitestriped flowers on dainty stems. The colour shows up particularly well in dappled shade and it spreads by seeding itself freely where it is happy.

QUESTION: I would like to plant a purple-leaved acer but I garden on chalk. Will I have to grow it in a pot? Does it need shade, or can I put it in a sunny position?

ORACLE: For some reason many gardeners are afraid of acers, imagining them to be delicate and difficult creatures. The Japanese maples are generally easy to grow plants that are tougher than many think. They are quite hardy and do not need protection from frost. The only cold damage they suffer is from late frosts, when the new leaves are soft and they catch the early morning sun. Although they are not keen on shallow soil over chalk they will grow in alkaline soils, and they are happy on chalk if there is reasonable soil depth. The purple leaved varieties such as Acer palmatum ‘Bloodgood’ need plenty of direct sunlight for best foliage colour, so position in full sun or semi-shade. Acers do not like to dry out at the roots, this causes browning and curling of the leaf tips. Their worst enemy is cold wind early in the season when the leaves are unfurling, so plant in a sheltered position or shield them with another larger, wind resistant, evergreen shrub.

QUESTION: I grow my hostas in containers to avoid slug and snail damage. Some are now getting too crowded in their pots. When is the best time to divide and replant them?

ORACLE: I always divide and re-pot my hostas in early spring – sometime in late February or early March. Usually by then it is easy to see where the new shoots are going to rise from and so decide where to make a sensible division. Prise the plant out of its pot and shake off some of the soil. Place on the ground and split the clump by plunging two garden forks back to back into the plant where you want to split the clump. As you pull the handles apart the two halves will be divided. Repeat until you have divisions with three to five shoots. Re-pot in John Innes No. 3 with a small handful of Osmocote added to each pot.

QUESTION: I have had a good crop of runner and climbing French beans. I have left some of the older pods on the plants to swell and produce seed. Can I dry these and save them for next year?

ORACLE: The simple answer is yes. You can leave the pods on the plants until the pods wither and start to split, then lay them out on newspaper indoors in an airy place until completely dry. Open the pods and remove the seeds. Store them in a cool, dry place in a paper envelope. If you store in an airtight box as often recommended you must make sure the seed is completely dry.

Whether it is worthwhile is always debatable. If rust or other diseases have been a problem the seed may carry them to next year‘s crop. As the beans will have been open pollinated, the offspring will not be identical to their parents, they will be variable. Next year they will probably be fine but, if you save seed in subsequent years, quality will gradually degenerate. Personally, I would go out and buy a new packet every year.

QUESTION: A young Robinia ‘Frisia’ in my garden has had very poor leaves this season. It was slow coming into leaf this spring and the foliage has got thinner as the year progressed. It looks as if it is dying – what do you think has caused its failure?

ORACLE: All Robinia pseudoacacia ‘Frisia’ seem to be in trouble. Even large established specimens are displaying bare branches and many have died. The first signs of a problem seem to be the appearance of fungal spots on the leaves and curling and browning of the leaf edges. The leaves start to fall early in the season leaving parts of the tree bare. Various causes are blamed, but at the end of the day a fungal disease is blocking the vessels that carry water up the tree. This causes stress to the plant resulting in its failure. There is no known remedy I am afraid. The problem is stripping our gardens of our most popular golden foliage tree. If you lose one I do not recommend you replant. Instead opt for Gleditsia tricanthos ‘Sunburst’ shown on the left.