Your gardening questions answered: What’s wrong with my climbing roses?

I planted some climbing roses into pots at either side of our garden gazebo and have trained them to grow up over it. I’ve been careful to feed and water them, and they did brilliantly for a couple of years, but last summer they looked miserable. Any suggestions as to what I’m doing wrong? TJ, Co Kilkenny

It sounds as if your climbing roses have slowly but surely run out of root space and nutrients. This is much less likely to happen to plants growing in the ground, as their roving root systems can quest far and deep in search of water and nutrients to sustain them. But most shrubby plants will naturally run out of steam over three to four years when confined to a container, even when they are top-dressed and fed with fresh compost and some slow-release organic fertiliser each spring. In this case, the answer is to either repot them or to plant them in the ground.

You don’t mention the size of the containers you’re using, but this will also have a bearing. The bigger the better is a good rule of thumb when it comes to growing any long-lived shrub or climber in pots, especially roses, which are naturally hungry, thirsty plants. Not only will large containers at least 60cm in diameter and height give them more root space but it will also offer them greater protection from frost damage and drought.

Unlike rambling roses, climbing roses also need an annual prune to keep them in good shape, another possible reason why your plants are looking sickly

To find out if your roses have become pot-bound, examine the base of the containers for signs of the roots attempting to escape through the drainage holes. If they’re badly pot-bound (which they almost certainly are), you’ll need to carefully excavate them from their containers and then neatly trim away about a quarter to a third of their rootballs with a sharp knife or secateurs before immediately repotting them using fresh John-Innes based compost enriched with a little, very well-rotted manure and then watering them generously. To encourage good drainage, place a few broken crocks over the drainage hole before repotting and place a few pot legs beneath the base of the container to elevate it slightly off the ground. Good drainage will also help to protect against common rose diseases such as blackspot and mildew, which were a problem last year as a result of wet weather.

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Unlike rambling roses, climbing roses also need an annual prune to keep them in good shape, another possible reason why your plants are looking sickly. November-March is the time to do this, when the plants are in winter dormancy rather than active growth. Use a sharp, clean secateurs and follow the rule of the three Ds as you do so (remove any dead, diseased or damaged stems). Then cut all the old flowering side shoots on the plants’ main stems back by roughly two-thirds to leave roughly two to three strong buds per side shoot. Finish off by gently tying the main structural stems on to horizontal training wires securely attached to your gazebo, spreading them out across the wall or garden structure to maximise the display.

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