Carol Klein answers your gardening questions

Carol says: "One honeysuckle in particular, Lonicera 'Halliana' (which does have yellow flowers) is particularly prone to powdery mildew. Although it disfigures the plant, it doesn’t kill it. Uneven watering is often the cause of mildew, I suppose the weather conditions this year, torrential rain followed by drought could have contributed. Give it another chance, it is always a shame to get rid of an established plant especially one with such fragrant flowers (even if you can’t reach them). It is semi-evergreen which compounds the problem. Try cutting it back hard in late autumn, untangling any top growth and disposing of it and any fallen or mildewed leaves. Keep the base of the plant clear and over winter when the soil is wet apply a thick mulch preferably of home-made compost."

We have an autistic grandson who puts leaves/flowers in his mouth. Which plants are safe to grow in the garden? He does not recognise danger. Linda

Carol says: "What a very difficult question, so many plants can be dangerous if consumed. The RHS publishes a list of potentially harmful garden plants. It is a long list! Does your grandson do any gardening? It might help if he could join in growing herbs and vegetables perhaps in a segregated area or a raised bed and possibly learn that some plants can be eaten whereas others cannot. I am not qualified to give you better advice. The National Autistic Society might have better advice."

What is the best plant for sandy, dry soil and shade? Diane

Carol says: "First things first, to give any plant the best chance of success in these conditions, try to increase the ability of the soil to retain moisture by adding homemade compost and/or leaf mould and watering the planting hole well, even more important if shade is caused by overhead deciduous trees. There are any amount of spring woodlanders which should be happy from snowdrops (always plant bulbs deeply) to wood anemones. Epimediums are the go-to plant for dry shade. Geranium macrorrhizum, Geranium nodosum (watch out it can be too successful), Geranium maculatum, Geranium sylvaticum, (anything with sylvaticum – meaning ‘of woods’ will probably thrive. Gallium odoratum (sweet woodruff) will cover the ground (in a friendly way). Japanese anemones should be happy and foxgloves and Campanula latifolia (both natives) should do well."

• Best plants for dry shade

I got some free lavender cuttings a while back and put them in some gritty compost but although they haven’t died they haven’t grown much. On investigation I found that the roots have not gone into the compost at all but stayed within their original plug shape. What went wrong and can I recover them. Liz

Carol says: "It is not clear whether or not the cuttings already had roots when you received them, I’m assuming they did in which case carefully take them out having watered first and gently tease out the roots which may be going round and round. Trim them with sharp scissors to about 4inches, 10cm, this will stimulate new root growth, and repot into fresh loam-based compost with added grit, making sure not to fold the roots. Keep them in a bright place but out of direct sun. Good luck!"

• How to take lavender cuttings

My euphorbia is flopping on the ground, do I cut back in autumn and should they be staked during growth? Val

Carol says: "Presumably this is one of the taller herbaceous euphorbias such as Euphorbia palustris. Mine have the same problem, after flowering, stems spread. It is a great idea to stake early on using canes and string tied to the canes not the plant or Y stakes. Many euphorbias have fiery autumn colour, it would be a shame to miss it. I cut back stems to the ground (mind emerging buds) during late winter/early spring. This is just about the only time I wear gloves – the milky sap from cut euphorbia stems can burn skin."

When and how is the best time to split up a large peony? Gill

Carol says: "Early spring is the ideal time to split peonies though not when it is frosty. Dig up the whole plant carefully and remove as much soil as possible Amongst the tubers you can see eye buds, the resting buds that will make next years growth. Examine it thoroughly then using a sharp knife cut it into separate pieces ensuring each has tubers, roots and at least one eyebud. Pot individually in peat-free compost or if conditions allow, replant into the soil having improved the site with organic matter. Always plant just under the surface of the soil, if you plant too deeply it may never flower. In any case new divisions may take a couple of years to get back into their flowering rhythm."

I am struggling with succession planting. Whilst spring bulbs are dying back, nothing else has flowered so the front garden looks really messy. Any top tips? Veronica

Carol says: "Try interplanting with early-leafing perennials, aquilegias, hemerocallis and thalictrums are some of the best. Usually gardeners plant their bulbs around their perennials. Do you renew your bulbs each year or leave them in situ? You might consider lifting all your bulbs in late autumn, enriching the soil then planting up some perennials and replanting your bulbs around them. It's especially important to choose perennials that suit your soil."

• What to plant with spring bulbs

Can you grow daphnes from their berries and will they come true? Alex

Carol says: "If a daphne is making seeds, it is likely to be a species or a selection from a species and as such, seedlings should be similar to their parents, having said that, every seedling is an individual. The only way of guaranteeing a plant is identical to its parent is when it is produced vegetatively as a cutting or a layer in which case it is a clone. Berries should be red and ripe and the fleshy part of the berry should be discarded by rubbing off the flesh. All parts of all daphnes are poisonous."

How do you stop a wildflower area of the garden becoming an untidy area? Glyn

Carol says: "Presumably you are talking about a meadow area composed of perennial wildflowers and grasses. It is difficult to avoid ‘messiness’ if you are allowing flowers and grasses to set seed and distribute it before you mow but it doesn’t last long. By late August, early September, most plants will have shed their seed. Try to mow when the weather is forecast to be dry for a few days and leave the mowings in situ for two or three days giving them a shake before removing them. Always remove mowings; leaving them enriches the soil and the aim is to keep it poor."

• How to create a wildflower meadow

What is your secret to growing nerines? Mine never flower. Sue

Carol says: "Sunshine, poverty and overcrowding is the recipe for success. When soil is rich and nutritious, nerines spend a lot of time during the summer making lush leafage and may not need to flower. Where bulbs are challenged they are more likely to flower in the autumn after foliage has died down. They need sharp drainage but should be watered in dry periods. Despite not relishing rich conditions, an occasional high potash feed, tomato feed is good, will promote flowering. When planting, whether in pots or open ground, always ensure that at least a third of the bulb is protruding above the soil or compost. Allow clumps to become congested."

We have three 'Mrs Bradshaw' geums in our hot border that have been wonderful during May and June but are now showing signs of going over. Should we now cut these back and what should we replace them with to continue summer colour? Graham and June

Carol says: "Yes, do cut back flowering stems to the ground, although some geums including 'Mrs Bradshaw' make viable seed (you can collect it and make more plants). If it is the variety’s bright red colour that attracts you and you want more for later there are many dahlias that will provide it, some with dark leaves, D. ‘Bishop of Llandaff’ being the most celebrated. With regular deadheading they will keep your border aflame through to the frosts. Crocosmia, red lobelias and penstemons are just a few of the options."

Please can you advise how I can stop roe deer eating the plants in my borders, they decimate my roses, day lilies, hostas and phlox, in particular. Lesley

Carol says: "I feel like saying if you find something let me know – we have a deer problem, recently someone left the bottom gate open and the deer moved in decimating roses galore and rendering one area a flower-free zone. Our best bet so far are motion-activated sprinklers only trouble is we sometimes forget to turn them off and get an accidental shower. Fencing is the only foolproof method but it is expensive – It needs to be 6 feet, 2 metres high."

More gardening advice from Carol Klein:

Carol Klein's favourite easy summer flowers