I’m attempting to answer the top 100 gardening questions I get asked on line, at talks and lectures, by post or out and about in garden centres and nurseries. It’s surprising how often the same questions crop up; I suppose all gardeners have the same problems. Do post your comments and questions at the end of the post and make sure you share my tips though your friends using social media. This is my third post – thirty down and seventy to go – so lot’s more gardening to talk about!
Q 21. I have a number of carex in the garden that have been there for several years. Although they survive they now look very unkempt and tangled. Some of the leaves are very long and some are brown towards the tips. Can I cut them back and will they regrow?
A. The foliage of carex, the sedges, does tend to get tatty, particularly if the plants get dry or are in sunnier positions. You can trim them back in the spring with a pair of scissors and they will then produce clean, fresh leaves. It is a good idea to feed at the same time with a slow release balanced fertilizer and keep the plants well watered.
Q22. My tall conifer hedge is suffering. Last year the greenery started to go brown. I thought it was due to lack of water and feed, so I watered and fed it regularly. It did not get any better. Then I was advised it may be due to infestation by aphids, so over the past nine months I have sprayed regularly with an insecticide. It seemed to do the trick, but recently the hedge has again deteriorated. Can you advise me if I should use a different insect killer? Or otherwise?
A. I imagine your hedge is x Cupressocyparis leylandii? This is particularly susceptible to aphid attack. The problem with recovery from an attack is that it is slow. There are limited chemicals available. If you have been using a chemical insecticide then I recommend you try one of the nature friendly ones based on natural pyrethrins. These are kinder and can be just as effective on an aphid attack. However this problem is often exacerbated by clipping too hard into old wood in the first place; this can be reluctant to regrow. Try drenching with an organic growth stimulant based on seaweed and feed the hedge with a slow release fertilizer. You will find this more effective if you mulch with garden compost at the same time and water thoroughly.
Q23. I have two catalpa trees, one golden (Catalpa bignoniodes ‘Aurea’) and one purple-leaved (Catalpa erubescens ‘Purpurea’) bought a few years ago as small plants. Unfortunately I am now going to have to cut them back and reduce their crowns by about fifty percent. I will do this when the leaves have fallen but are the trees likely to survive such drastic treatment?
A. Your catalpas will have no problem with being cut back hard, as long as you do it in winter when the trees are dormant. They will respond with vigorous growth and larger leaves, but probably won't flower in the first year after pruning. You can in fact grow either catalpa as a stooled shrub, as you can paulownia. The Victorians used both as bedding "dot" plants and they are becoming increasingly popular in exotic bedding schemes.
Q24. I planted a lovely Skimmia japonica ‘Rubella’ in my garden last winter which looks fairly healthy but the flower clusters are small and the leaves have turned yellow. Is my soil the wrong type for this plant; I’ve heard its best on acid soil and I’m not sure if mine is?
A. Skimmia japonica ‘Rubella’ is the most popular skimmia sold in large numbers in the winter months. It is a male form so produces no berries but it has highly decorative red bud clusters which open to fragrant spring flowers. It can be very sulky as a garden plant and that is often blamed on the soil type. Contrary to popular belief it does not need acid soil, but it does need shade. In sun the foliage turns yellow. The small flower clusters may mean the plant is a little starved; feed with slow release general fertilizer and mulch with compost. Alternatively transfer the plant to a pot and put it in a shady position.
Q25. I have a conservatory that is heated to some extent in the daytime but gets cold at night. I like the idea of growing a lemon in it. Will it work, or will it be too cold at night?
A: Citrus, especially most varieties of lemon are tough plants that will even stand a few degrees of frost. Your lemon will be very happy in your conservatory over winter and should flower and bear fruit during the winter months. If the weather is extremely cold keep the compost on the dry side but make sure you give it enough water when temperatures rise in spring. From the late spring your lemon will be happier out on the patio or doorstep. Conservatories, even shaded ones can get unbearably hot in summer so it will be happier outside and flowers stand a better chance of pollination. Keep an eye open for spider mite and scale insects on the foliage. Misting the foliage regularly with water helps reduce the chances of spider mite.
Q26. In the recent gales I lost a large laburnum tree which has left quite a gap. It grew against a country hedge of hawthorn, blackthorn and holly. Space s not a problem, but I would like flowers and ideally fruit; the laburnum was glorious in spring but not so exciting for the rest of the year. Any suggestions?
A.My favourite tree for this type of situation is Malus hupehensis. This is a lovely round headed tree with a cloud of white flowers in spring which are delicately fragrant and filled with nectar and pollen for bees. These are followed by small bright red fruits that hang in clusters in autumn. The foliage is dark green and healthy and perfect with both flowers and fruit. It would fit in perfectly with your hedge and would give two seasons of interest.
Q.27. I have a number of heucheras in the garden that I’ve had for several years; some in pots and some in the open ground. I’ve managed to keep vine weevil away using biological control but they are now rather woody and crowded with short knobbly stems coming from the base and the leaves are much smaller. Is it time to start again?
A.You can rejuvenate old heucheras by pruning, as odd as it may sound. I recommend that you wait until spring. Take a sharp pair of secateurs and cut the oldest, longest stems back leaving about 1 cm (0.5 inches). Feed the plants with slow release fertilizer and mulch with some fresh multi-purpose compost. Quite soon they should start to produce new shoots and much larger more vigorous leaves.
Q.28. I have a large pine tree in the garden where nothing seems to grow. The ground beneath is thick with pine needles and very dry. Whatever I plant there fails. Have you any suggestions?
A.The ground under pines is notoriously difficult to get plants to grow in. Although its often not as shady as it is under other trees the roots are near the surface which makes it a very hostile environment to try to establish anything. The secret of success is to only go with things that might succeed, rather than things you like. I fine small leaved varieties of Hedera helix work well, as do any of the varieties of Vinca minor. If you plant Cyclamen hederefolium with these the cyclamen leaves and flowers seem to battle through quite successfully. Berberis and mahonia both seem to succeed. Try Mahonia japonica and one of the small evergreen berberis such as Berberis stenophylla ‘Etna’. Of course the real survivor in ry shade is the Butcher’s broom, Ruscus aculeatus. This can look effective if you combine it with a variegated ground cover ivy.
Q.29. I have a few ancient roses in a border that I would now like to remove and replace. I want to plant some new English roses in their place. Do I have to remove and replace the soil? I was told that I should bury a cardboard box in the ground and plant into that. Does it work?
A.Actually there is no need to replace the soil or plant in a box. Remove the old roses and then add plenty of shrub and tree planting compost and cultivate the ground well. When you have dug the hole for the new plant sprinkle dried mycorrhizal fungi into the bottom of the planting hole. This develops into a mycelium which forms a relationship with the rose roots and overcomes any problems of rose replant disease. You can use Vitax Q4+. This is a balanced slow release fertilizer with added mycorrhizal fungi which will get your roses off to the best start.
Q 30: Can you recommend some shrubs for a windy, cold corner of my garden. My soil is heavy clay and can be wet in winter.
A: Any of the pyracanthas are a possibility and the ‘Saphyr’ varieties are especially hardy. These are often seen trained against walls or fences but they also make excellent free standing shrubs. Berberis thunbergii seems to be very resilient to wet and dry conditions and all varieties have good autumn colour. Berberis thunbergii ‘Starburst’ is one of the most spectacular in autumn and has an attractive arching form throughout the year.
All varieties of Cornus alba cope with both wet and exposed sites and now is a good time to think about planting them for their attractive winter stems. It may also be worth thinking about a small tree, this would give some shelter and help to diffuse the prevailing wind. Any variety of Sorbus aucuparia would be good; they all have light foliage, spring flowers and attractive autumn berries.