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