Ask Adam: part four

Your questions answered

We recently invited you to submit your gardening questions for Adam Pasco, editor of Gardeners' World Magazine. View Adam's fourth set of answers, below.

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
Book online quote code GWNE




I'm keen to grow some squash on my allotment, but am running out of space. I've heard you can train courgettes up a frame – can you do this with any variety or do you need a special sort? Also, what about butternuts and pumpkins? From Sandra2

Adam says: Most edible varieties of squash are bush varieties, but I have grown quite a vigorous climbing courgette called 'Tromboncino' up a strong wigwam of sticks. This variety produces a rather long, curved green fruit, but very tasty. There is a shorter climber called 'Black Forest' that reaches about 1.2m, but no others I can recall. Most form a bush, although some do scramble a short distance.

Larger fruited varieties of pumpkins and marrows would not be suitable, as their heavy fruits could not be supported in the air. However, I've grown a mini 'Jack Be Little' type of pumpkin called 'Hooligan' as a short climber in the past. Where space is limited try planting squash varieties in the spaces between sweetcorn. I'd recommend sowing or planting sweetcorn out in blocks about 45cm apart in each direction, leaving plenty of room to plant courgettes and squash in between.

Several trays of bedding easiplants have just arrived. I do not have a greenhouse. What would you advise? Leave them in their trays until mid May? From Rosieleaf

Adam says: You really should pot up these small plug plants into larger pots. I use 7-10cm pots depending on the size of the plugs, potting with a multi-purpose peat-free compost. Conditions are still too cold to place these outside unless you can provide some form of protection. If you don't have a greenhouse you'll need to grow bedding plants on a bright windowsill. They'll grow quickly to produce large plants for using in patio pots and bedding displays in late May or early June. Remember that no tender bedding plants can be planted out before the last frost in your area, or plants will be badly damaged or killed.

I'm growing bedding plants from seed this year in my greenhouse. They're coming on well, but I'm wondering when to start to feed these plants. From gerard andrews

Adam says: As a rule of thumb, most potting composts only contain enough food to keep plants going for about four weeks. I would recommend adding a general feed to one watering a week after this. Once strong plants have developed, change the fertiliser to a high-potash brand, like a tomato fertiliser, to encourage more flowers to form.

When planting out bedding into patio pots or baskets I always mix some slow-release fertiliser granules into the compost. These dissolve very slowly to feed plants all summer.

Can I grow snowdrops from the seed pods that I collected this year, and how do I go about it? From tony ralph

Adam says: Once areas of snowdrops have established they naturally reproduce by both bulb division and seed. I just leave seed pods to form and ripen on the plants, letting them fall onto the surrounding soil.

If you have picked the seed heads off then I hope you waited for them to fully swell and ripen first. You can then either sprinkle seed onto the soil in areas you would like snowdrops, or sow onto the surface of pots of loam-based seed compost. Cover seed with grit, place in a frame, and keep watered. The seedlings that emerge will form bulbs, but these won't reach flowering size for a few years, so require regular care to raise them to flowering size.

Which climbers would be best to plant on a south facing fence or trellis? From Jackie Simmonds

Adam says: You've got quite a few to choose from, and the climbing plant section of good nurseries and garden centres should have a few to tempt you. My favourites include clematis, and here you can choose varieties for spring, summer, autumn or winter flowers. Golden-leaved jasmine looks good combined with fragrant honeysuckle. Although very vigorous, perhaps consider the chocolate vine (Akebia quinata) and golden hop.

I'm also a fan of training shrubs up against fences such as cotoneaster, pyracantha, Solanum crispum 'Glasnevin', ceanothus, euonymus and many varieties of climbing rose. While shrubs are getting established try growing annual climbers up your fence like sweet peas, Cobaea scandens, morning glory or Mina lobata.

I produce my own compost in a compost heap and wormery. When I used it this year it contained seeds from previous years that started to grow with my new seeds. How do I make sure the compost is clean? From Rose 2

Adam says: Firstly I would try and avoid adding any material to worm or compost bins that contains seed, particularly weeds. Neither composting process is likely to kill seeds. To achieve this you would need to use an insulated compost bin that allows heat to build-up inside to a high enough level to kill seeds.

Working in large gardens in the past I have used large pieces of equipment that heat-up to sterilise compost, but these would not be viable for home gardeners. I have heard of people using their microwave to steam sterilise small batches of compost, but I wouldn't do this.

For seed sowing I would always prefer to use bagged seed compost that I know is reasonably sterile. Keep you home-made compost to mix into your potting composts or soil instead.

Is it necessary to pinch out the tips of shoots of dahlias grown from seed to produce bushier plants? From Tilly3

Adam says: Yes, I would, or some varieties will just develop a single stem with no side shoots at all. Pinching is a much under-used technique, and I pinch out the tips of many bedding plants, flowers and crops including sweet peas, peppers, aubergines, pinks, petunias, verbena, and many others.

I'm trying to discover when to plant out runner bean seeds. I haven't done anything yet other than harvesting seeds from last year's beans. From Julie Higgins

Adam says: Please to hear you've saved your own seed from last year, and saved a bit of money too! Runner beans are quite tender, so can be damaged by cold, wet weather. In most areas the soil should be warm enough to sow seed outside from around mid to late May. Sowings can continue through June if conditions in your area are still cold.

Alternatively, sow seeds in deep modules or tubes, like old cardboard toilet roll tubes, from about mid-May. Raise plants on a warm, bright windowsill or in the greenhouse, and plant out at the base of canes in early June.

Is it too late to cut back dogwood (Cornus) in mid April? The plant already has leaves. From margaret davison

Adam says: Although I'd always recommend pruning dogwood in winter, or March at the latest, you could still prune a little now. I would probably just shorten about half the shoots at the front of the shrub, cutting them down to a woody base. New shoots will grow up from here later in spring. Just nip out the tips of any very tall shoots at the back. Your display will look a little bare before new growth develops, but plants will be fine. Now make a note in your diary to prune your dogwood in February/March next year.

How do I prune blackberry and raspberry canes? They've gone native and are lethal! From Sarahsjmmoore

Adam says: Your first job is to buy yourself a pair of thorn-proof leather gloves, and some sharp secateurs.

Blackberries produce flowers and fruit on the new canes they produced last year. Any older canes that carried fruit last year need to be cut away completely at soil level. Train the remaining canes to supporting wires running horizontally between posts. When blackberries produce really long shoots I train them vertically then arch them over and round, tying them to supports in large circles.

If cane growth is still too congested, selectively remove a few canes at ground level to provide more space for the remaining ones.

Summer-fruiting raspberries produced also produced new canes last year that will carry fruit this summer. Cut out any remaining old fruited canes. Now cut off canes growing some distance from the main row. You are aiming to tie these new canes vertically to supports about every 10cm, so any excess canes can be pruned away at the base.

Autumn-fruiting raspberries carry fruit on the new canes that grow this year. Cut away old canes, and toe new ones to supports as they grow.

I grew some potatoes in the garden last year. Some of the crop must have been left in the ground as I've noticed potato leaves growing up through the ground. Will these produce edible potatoes this year, or should I bin them? From Miss C

Adam says: There's no reason why these rogue potatoes shouldn't crop well, provided your potatoes did not succumb to blight or disease last year. Diseases can carry over from one year to the next on crops like this, so beware. That's why the best practice is to buy seed potatoes each year that have been certified as disease free. However, if your crop was healthy last year why not treat these potatoes as if you'd just planted them, covering tips to protect them from frost. Then start pulling soil up around stems as they grow, burying sections to encourage more tubers to develop.

Ask Adam: part one

Ask Adam: part two

Ask Adam: part three

Ask Adam: part five

Ask Adam: part six