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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Hi, I live in the north east of Scotland. Why don't my camellia bushes flower? From Cir Mhor
Adam says: I wonder whether your plants have formed flower buds that have then fallen, or haven't they flowered at all. As acid-loving plants, when planted in ericaceous soil or compost camellias usually flower reliably from a young age, whether in large pots or garden soil. They prefer a position out of scorching sun and drying winds, and require regular watering during summer to keep soil moist.
Feed plants at least once a year with a specific camellia fertiliser, iron sequestrene, or one formulated for acid-loving plants. Make sure that from late summer and through autumn camellias never go short of water. This is the time when plants are developing flower buds at the tip of shoots. Shortage of moisture can result in no flowers forming, or flower buds start swelling that fail to open.
My daffodils are coming up with only green leaves, but no flowers! What shall I do? Throw them away? From dg43
Adam says: There are a number of possible causes, and it would be useful to know whether these were newly purchased bulbs planted last autumn or an established clump. If would also be helpful to know whether the daffodils were planted in the garden or in pots.
Newly purchased bulbs contain all they need to flower, but if planted in patio containers that got waterlogged and frozen over winter the flower bud in the heart of the bulb could have been damaged. Some leaves may grow, but no flowers will form.
Bulbs growing in established clumps in the garden naturally divide and multiply each year, and as they become more congested the amount of food and water available to each bulb diminishes. These bulbs fail to form flowers, and clumps become 'blind'. Avoid this happening by always drenching soil round bulbs with liquid feed after flowering. Lift and divide clumps in August/September every 3-4 years, replanting them at wider spacing in well-prepared soil.
A pest called narcissus fly also causes bulbs to be blind, as the maggots eat away at the flower bud in the centre of the bulb. You can check if this pest is the culprit by digging up one bulb and cutting it open to see whether a maggot lies within. If it does then bulbs are best discarded and replanted with fresh stock next autumn.
Can you plant onions outside now? From dan
Adam says: Yes, onion sets can be planted directly outside from March onwards, provided soil conditions in your area are not frozen or waterlogged. Plant heat-treated sets, as these should not bolt and run to seed if conditions turn cold again. However, if the weather remains cold and wet plant onion sets individually in small pots or modular trays of compost. Start them into growth in the greenhouse or cold frame, and plant out later in April once they've developed strong shoots and roots. Seed raised onions grown in small pots can be planted out when large enough, but I'd keep these under cover to reach a larger size, and plant outside during April.
For the last 2 years I've tried unsuccessfully to grow summer squash. First year outside, second year in the greenhouse from seed. Each time flowers appear but no fruit. Is it lack of pollination? From boyedmund
Adam says: I think you've identified the problem yourself. All varieties of squash, including marrows, courgettes, pumpkins, etc, produce both male and female flowers. Look carefully at a flower and if you see a swelling just behind the open petals then this is a female bloom. Male flowers do not have this swelling.
Although there are a small number of self-fertile courgettes (like 'Parthenon') all others need to be pollinated, and that requires bees or insects to carry pollen from an open male flower to a female one.
Problems arise when female flowers open but with no male flowers open at the same time to provide pollen. No pollination – no fruit! Lack of insect activity can also be a problem, particularly under glass. You can lend a hand by picking off open male flowers and dabbing their pollen inside female ones.
However, to ensure a good supply of male flowers you will have to grow several plants of the same variety. If space only permits you to grow one or two plant you may be unlucky, and better off growing an alternative to squash.
Is now the right time to dig the rye grass I've been growing as a green manure into my veg patch? From Sue M
Adam says: Green manures are crops specifically grown to be dug into the soil, adding nitrogen and improving soil structure. Green manures can be dug deeply into the soil to bury them at almost any time. I like to do this at least 3-4 weeks before I plan to sow or plant crops in this area. This gives the green manure time to start breaking down, and for the soil to settle.
A range of different green manure varieties are available to sow and grow right through the year, helping you make the very best use of empty spaces.
I have a 4ft by 6ft greenhouse and would like to add some ventilation to it, is this possible? From Speedy2
Adam says: It's essential to provide good greenhouse ventilation, particularly during summer to prevent temperatures soaring. A greenhouse fitted with both high and low level vents helps create good air circulation, and you should also open the door completely on hot days.
Most aluminium greenhouses are constructed in a modular system using glass panels about 60cm (2ft) wide. Louvre vent kits are available to replace single panes of glass. Check greenhouse equipment suppliers to see whether their louvre vent kit is suitable for your greenhouse.
Top Tip: sprinkle water over the greenhouse floor every morning on warm summer days to increase humidity, and reduce stress caused by high temperatures.
A hard white crust has appeared on top of the compost on most of my indoor plants. I have tried taking the top half-inch of compost and replacing it with fresh but it just comes back what do I need to do? From Fuschia16
Adam says: White mould will regularly develop on the surface of compost if it remains moist. This is commonly found on peat-based compost. It shouldn't be causing any problem to the plants, so can just be ignored. I'm not sure what indoor plants you're growing, but I'd try and keep the surface of compost drier. Do you water your plants from above? If so, try and water from below instead by standing pots in trays of water rather than soaking surface compost every time you water. Also, only water when plants need it.
How can I stop ground elder creeping across from next doors garden? I've covered it with cardboard to exclude the light, but this isn't a long-term solution. From Kay from Surrey
Adam says: Smothering perennial weeds with cardboard or a weed-suppressing membrane is a great way to exclude light and prevent weeds growing on large areas of ground. I've experienced the same problem with weeds growing through the soil from a neighbours garden, and you have a couple of additional options.
Firstly, you could bury a vertical barrier deep into the ground along your boundary to prevent weeds growing through. The barrier really needs to go down at least 30cm, so this isn't an easy job. Make barriers out of heavy duty polythene or a similar material that's impervious to roots.
Secondly, regular application of a systemic weedkiller containing glyphosate could help. By treating any new ground elder shoots popping up in your garden, the weedkiller will travel along the roots and kill them. Repeated applications should pass through roots and back under the fence to kill the source of this infestation.
One last thought – perhaps you could encourage your neighbour to control their weeds, or ask if you can pop round and treat them with weedkiller yourself.
I've had my Wisteria for about seven years. It has lovely green leaves in summer and is spreading out along a fence in a sunny position, but has never flowered! I have followed all the advice about pruning it twice a year and mulch it well in spring. What am I doing wrong? From Fran26
Adam says: You have been patient! These are several possible reasons for lack of flowers: 1. Did you buy a named variety of wisteria? If the plant was un-named then it could have been seed raised, and this will be very slow coming to flower, with no guarantee of flower colour or quality either. Named varieties have usually been grafted, and come into flower more quickly.
2. Are you pruning correctly? During the first few years after planting you'll have taken leading shoots and trained them onto support wires, along walls or over arches and pergolas. While the leading shoot will be left unpruned to extend the branch framework, any sideshoots growing from this need pruning twice a year. In July all long, whippy sideshoots can be cut back to about 25cm. Then during winter these same shoots are shortened still further back to 1-2 buds. Pruning in this way helps produce flowering spurs along the length of each stem.
3. Perhaps your wisteria is just growing too strongly in very rich soil, and is enjoying the vigour of youth! Trick it into flowering mode by feeding it a high potash diet this year. Potassium is the major plant nutrient required by plants to support flowering and fruiting. Sprinkle sulphate of potash fertiliser over the soil around the plant now, watering it into the surface before covering with a mulch of compost. During summer, water every fortnight with a solution of high potash tomato fertiliser.
We have lots of established beech hedging in our "new" country garden near Alyth (Perthshire, Scotland), which we have pruned to about 2m high. I'd like to soften them and add seasonal interest with a rambling rose, and maybe clematis and honeysuckle. Can you suggest suitable varieties? From Christine Love
Adam says: I would be cautious about treating a living beech hedge as a plant support system. The weight of vigorous climbers, like roses and honeysuckle, could harm the hedge, making it impossible to cut, and kill sections of it. Mixed planting in thorn hedges is more successful than with a formal beech, privet, laurel or conifer hedge.
However, some less vigorous climbing plants can be planted at the base of formal hedges and left to scramble up through them for support. You may be able to achieve this with late flowering clematis, like varieties of Clematis viticella. This clematis will die back after flowering, and can be cut down to soil level each winter. You may just get away with pruning your hedge in September, and cutting back the clematis at the same time.
I've also seen the Chilean Glory Vine, Eccremocarpus scaber, growing successfully in hedges. Raise plants from seed in pots under glass, and plant at the base of your hedge in June. You'll need to water it regularly, as the soil here will be very dry, and plants will struggle to survive without your help.
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Ask Adam: part six