Tony Dickerson answers your questions
Q What has happened to the leaves on one side of my climbing rose? Claudia Chalkley, Puckeridge, Hertfordshire
A It’s not out of the question that a late air frost has caught the foliage, but you’d usually see some obvious browning and curling of the leaves. What you have is tiny, deformed foliage, which is very characteristic of weedkiller damage. Roses are sensitive to even very small amounts.
In gardens there are numerous ways accidental damage can occur: l One of the most common is spray drift, which happens in windy conditions where the weedkiller drifts onto other plants. Only spray in calm weather and, to be extra sure you don’t damage plants, cover them with a plastic sheet which can be removed when the spray is dry. l In very warm, still conditions in summer, weedkiller can vapourise into the air and later fall back. To avoid this you should spray in a very gentle breeze and use an adjustable sprayer that delivers larger droplets. l Accidental damage can also occur where sprayers have been used previously with herbicide, but not washed out properly before use with other products. All spraying equipment should be triple washed after use with clean water and the waste applied to the original target area. It makes sense to have two sprayers – one for insecticides and fungicides and another solely for weedkillers. l Path weedkillers are residual in action, the chemicals remaining active for six months or more. Where over-applied or following heavy rain, it’s easy for run off from treated areas to flow into beds and borders. l Gardeners occasionally poison their own plants by using grass clippings as a mulch where the lawn has been treated with a hormone lawn weedkiller. Instructions on the product clearly indicate that usually the first three cuttings shouldn’t be composted or added to municipal green waste collections. l Purchased mulches, soil improvers, manures and potting composts can, on occasion, also be contaminated. This was a significant problem a few years ago. It’s less common now but still occasionally occurs.
Q How do I prune my rampant yellow Banksian rose – it’s a bit of a headache! Rosemary Lewin, Highcliffe, Dorset
A Rosa banksiae ‘Lutea’ is a large, earlyflowering, thornless, rambler with clusters of small, pretty, pale yellow, double flowers in late spring. It’s not as vigorous as some Banksian roses, but it can still make 6m (20ft), so isn’t the best choice for your modest arch.
Prune immediately after flowering in late spring. Cut out shoots that have flowered but the other strongly upright shoots have to be left because the flowers occur on wood produced the previous season. As such, it isn’t a good idea to tie in new growth during the summer as it makes it difficult to prune out the following year. Rather than trying to contain this rose by pruning, I’d extend the structure with a new arch 4.5m (15ft) away, with timbers between to support growth.
Q What’s my mystery houseplant? Mr J Walker, Thornton-Cleveleys, Lancashire
A It’s an epiphyllum or orchid cactus. They’re easily propagated from cuttings and make relatively trouble-free houseplants so get passed between gardeners without anyone necessarily knowing what they are. Plants produce large, showy flowers which are often sweetly-scented, but each lasts just a couple of days.
The reason your plant has failed to flower is probably due to repotting last year. It should be back to its glorious best next year. The other common cause of poor flowering is where plants are kept in too much shade. Aim for bright, indirect light. Q Why is our rhododendron turning brown? Patricia Tingey, Stranraer
A Rhododendrons are becoming increasingly difficult to grow in southern England as climate change leads to long periods of drought. A lack of moisture is unlikely to be the cause where you are in south west Scotland.
The browning could be the early signs of root disease, particularly phytophthora root rot. Dig down at the side of the main trunk to see if there are signs of decay on the roots, which may well be black and soft. If that‘s the case, lift the shrub and burn it. Dig out soil containing roots and replace with fresh from elsewhere in the garden, but don’t replant rhododendrons in the same spot. If the roots appear healthy I’d wait until spring, just after flowering, to see if there’s new growth. If no new leaves show, prune out damaged branches.
Q What’s the best way to propagate a rose? Ian Lyden, by email
A The simplest way is by taking hardwood cuttings of well-ripened wood of the current season’s growth in late autumn, about 30cm (12in) in length. Make an angled cut above the top bud and a straight cut below the bottom bud to ensure you get them the right way up. Dig over an area in full sun. Insert a spade to its full depth and push forward to create a narrow trench and fill with sharp sand. Dip the base of the cutting in Clonex hormone rooting gel and insert it in the trench to three-quarters of its length. Lift the next autumn.
Softwood cuttings can be taken any time from spring over the summer. Trim beneath a leaf node and remove the soft tip. Dip in rooting gel and insert up to six cuttings into pots of cutting compost made up of equal quantities of multipurpose and sharp sand.
Ideally, place in a covered heated propagator. Alternatively, cover pots with a polythene bag and vent them daily.
Q What caused the leaves on all my containergrown acers to wither? Martin Hewitson, by email
A Acers in containers can easily dry out, causing the delicate foliage to wither rapidly. However, I think it’s unlikely all your trees would suddenly wither, so the likely cause is the severe air frost that affected southern England about a month ago. Keep containers gently moist. Most deciduous trees will produce a second flush of foliage later in summer.