Every two weeks between now and Gardeners' World Live, 13-17 June 2012, Adam Pasco will be answering a selection of your gardening questions.
If you'd prefer to ask Adam a question in person, you can do so at the Gardeners' World Theatre at Gardeners' World Live, where he'll be appearing regularly. Save 10% on your show tickets by booking now:
Tel: 0844 581 1344
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I have five 'babies' growing off the main stem of my cordyline. Do I have to seal the main stem when I cut these off? From Wendy7
Adam says: Cordylines have really suffered in many gardens over the past couple of cold winters, and in some cases this has killed the top rosettes of leaves completely. Where new shoots develop from the main stem, these can be left to grow or can be removed by cutting right back flush with the main stem using a sharp knife. There is no need to seal the pruning cut, which should not 'weep' sap.
Where cordylines have been damaged by cold do be patient before digging up plants, as new shoots often develop from bare stems, or from around the base of plants. Some of these new shoots may have their own root system, and can be carefully dug up and potted or transplanted.
I have a ceanothus shrub in my front west-facing Somerset garden, and every spring most of the leaves turn brown. I usually cut these off, but then have very few flowers. It's about 3ft (1m) tall. Is it in the wrong place? From Angelique2
Adam says: Californian lilac is a beautiful shrub, usually producing blue powder-puff flowers in early summer, and many varieties are evergreen. If these leaves are turning brown early in the year then a few factors could be causing this. The most likely is dryness at the roots over past weeks and months. Drying winds will be removing moisture, and if there is no water in the soil for plants to take up then their leaves will turn brown and fall.
Extremely cold and frosty conditions, again with strong winds, can cause winter damage if planted in exposed gardens. As the evergreen leaves are quite thick this damage may not be immediately evident. Now spring has arrived you can see the brown leaves more clearly, but the damage could have been caused some time ago. This damage will also affect flowering.
It does sound as if your ceanothus could be growing in the wrong place, so perhaps move it. Otherwise regular watering to ensure surrounding soil does not dry out, and covering soil with a deep mulch of compost could help.
Is it safe to leave a tall, slim eucalyptus to continue growing without any pruning? It's growing next to a wooden fence, and swings about in strong wind. From J.Davey
Adam says: You don't say which variety this is, but possibly the popular grey-leaved Eucalyptus gunnii. This and other varieties really enjoy space to grow and be admired in all their glory. However, if it is in a small garden then pruning is essential. I'd recommend hard pruning each year to either coppice or pollard your tree. Both pruning techniques are best started when trees are young, and coppicing involves cutting the whole tree back to within a few inches of soil level. Vigorous new growth develops each year, carrying the juvenile leaves so loved by flower arrangers.
Pollarding isn't so extreme, and involves leaving a main stem about 2m tall, and cutting back all branches to this.
Always be cautious about planting tall trees in small gardens. Choosing the right varieties of trees and shrubs is important, as not only can plants outgrow their site but on some soils the excessive moisture they extract can lead to problems of subsidence, or damage to drains and foundations.
What flowering and evergreen climbing plants will be best to plant on a east-facing fence in County Durham? I don't get much sunshine in the back garden. From hellibore
Adam says: In this shaded situation you don't have a very wide selection of plants to choose from, but here are a few suggestions. To start with you could plant virtually any variety of ivy, with small-leaf variegated varieties in gold or silver adding interest all-year-round. The evergreen winter flowering Clematis armandii is worth considering, as is the chocolate vine, Akebia quinata. Although neither is evergreen, do consider Boston ivy or Virginia creeper, and also the climbing hydrangea (Hydrangea anomala subsp. petiolaris). As an alternative to a climber that grow on the fence, also consider growing evergreen shrubs in front of the fence, possibly trained to wires. A good choice here is Garrya elliptica, and the male variety 'James Roof' produces lovely long catkins during winter. Other evergreen shrubs that could suit these conditions include firethorn (Pyracantha), cotoneaster, photinia, camellia and euonymus.
My bergenias have a lot of dead areas on their leaves, but are managing to flower fairly well in spite of this. I have them in a sunny well-drained spot. What can I do for them? From jessgardener
Adam says: The older leaves on bergenia do die each year, with new ones growing from the tip of shoots. Just snip off the old leaves as they develop. Over time clumps expand and create gaps in displays, so the whole plant needs lifting, discarding old woody portions that aren't carrying any leaves, and replanting young pieces in freshly prepared soil.
As an evergreen perennial, bergenia likes woodland conditions, and dislikes extremely hot sites or dry soils. Spread a mulch of compost over the soil around them, and keep watered if soil starts getting very dry or more leaves will turn brown!
I sow various seedlings and put them in the heated propagator to start. I take them out as soon as two small leaves show, and keep them in my unheated conservatory. They then continue to grow and resemble cress rather than short, stubby seedlings that you see in your magazine. Where am I going wrong? From pybarlow
Adam says: Sowing seed too thickly causes congested seedlings to develop, and these can get drawn and leggy. Try sowing more sparingly and at wider spacing to avoid this.
Poor light conditions also cause seedlings to grow taller as they try and reach the light. Seedlings must be grown in full light, but away from scorching sunshine that could damage them. Very early sowings during February and March, when day length is shorter and light levels tend to be poor, also cause seedlings to get lanky. Don't sow too early. Delaying sowing by a few weeks until natural light levels have improved in late March and early April often produces stronger plants.
We want to plant up two raised beds with some perennials flowers/wildflowers growing around the area. The area is south-facing and open to the elements. We'd like some evergreens to give interest all year and some for summer colour. What do you suggest? From Lucy3
Adam says: You have a tremendous choice available, so do visit plant nurseries in your area and see what they have in stock. I'd certainly recommend growing hardy geraniums, lady's mantle (Alchemilla mollis), spreading evergreen ajuga and bergenia. A range of spurges could also do well here, from compact varieties like Euphorbia x martini to bold feature plants like Euphorbia characias 'Silver Swan'. Try getting a few flowering biennials established to pop-up around the area, like honesty and foxgloves – let them seed freely, and just pull up any seedlings growing where you don't want them. Also take a look at the many hellebores available, including Helleborus foetidus and H. argutifolius.
My clematis is pot bound. What is the best thing to do with it? I would like it to remain in a pot as my soil is clay, and it would be impossible to dig a hole big enough for it to go into in the ground. Presumably it cannot be split. From Tai Chi
Adam says: Unfortunately you do not say which variety of clematis you're growing, or how large the current pot is. I have several large flowered summer hybrids growing in large patio pots, and by large I mean about 40cm across and tall, or more. Where clematis is being trained up a support then the container needs to be large enough to accommodate an obelisk or frame on top. In this size of container, and when planted in a loam-based compost like John Innes No.3, the clematis should be happy for 4-5 years. After this I tend to replace with a healthy young new variety.
If your clematis is growing in a smaller pot than this then do consider moving it up into a larger one – not an easy job for one person, so you might need help. Despite being pot bound, by regularly feeding your clematis with a high potash fertiliser you may find it remains happy and continues flowering for many years to come.
I have a south-facing back garden, but have not had a lot of success growing rhubarb in beds for the past 2 years. I usually only get 2-4 thin sticks – most disappointing. What can I do to produce strong healthy plants? From Cherry3
Adam says: While the site may be suitable your soil may not. Rhubarb enjoys a deeply cultivated rich soil that locks-in moisture and supports strong growth. If planting new rhubarb, dig homemade compost or rotted manure into the ground first. Plant with the crown just at or below the soil surface and not too deeply, water well, and then spread a mulch of compost around the plant.
Did you plant too deeply, or not improve the soil well enough? If so, dig it up now and replant correctly. Rhubarb loves moisture, so do give clumps plenty of water through spring and summer if soil conditions are dry.
I have just purchased six bare-rooted roses that had lost their labels. I've potted them up and they all seem quite healthy. Is there any way to tell what type these roses are before they flower? From ritalilly
Adam says: No, I'm afraid not. There are a handful of roses with strong characteristics that an expert could identify from bare thorny stems or foliage shape and colour, but without a flower it's impossible to identify most roses accurately. Be patient, and once they flower in July/August number your roses 1-6, taking pictures of each and make a note of other features like scent, growth habit and so on. Then consult a rose expert, specialist rose grower, or one of the many pictorial books available.
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Ask Adam: part six