Gardeners´ Question Time Top 10 Questions

  1. 1. Why haven't my seeds germinated?
  2. 2. I have a shrub that doesn't want to flower
  3. 3. How to tackle invasive weeds
  4. 4. How do I identify my soil type?
  5. 5. How do I keep wood pigeons and other woodland creatures away?
  6. 6. How can I get rid of slugs?
  7. 7. Why won't my wisteria flower?
  8. 8. Please can you suggest some plants for a shady garden?
  9. 9. Which plants will add fragrance to my garden?
  10. 10.How do I control potato blight?

1. Why haven't my seeds germinated?

Anne Swithinbank

Seeds must be fresh and alive to germinate and will vary as to how long they last in average storage conditions. Carrot and parsnip seeds for instance, are notorious for losing viability quickly and it is always best to buy these fresh each year.

In theory, all a seed needs is ideal conditions regarding light, water and temperature. While most seeds germinate readily within a week, others may have turned dormant because they have adapted to avoid harsh conditions in the wild. To break this, some seeds need to experience a cold winter with periods of frost before they will come up. Others may need soaking to soften the seed coat and in some cases to wash away inhibitors. Gardeners often hasten things along by putting seeds in the fridge, or even soaking them in chemicals that mimic ash in the soil (several South African and Australian plants germinate after fires). If you've had problems with seeds of unusual plants, they probably just needed more time.

But what if you've failed with easy seeds like sweet tobacco sown into a pot, or lettuce seed in a drill? The most common pitfalls involve creating the correct seedbed:

  1. In a pot, press seed or multipurpose compost down lightly using a flat disc of wood, so the seed lands on a firm, moist surface and can't fall down chinks and channels in the compost.
  2. It is then covered lightly with a mere dusting of compost no deeper than the size of the seed.
  3. Press this again.
  4. Larger seeds can be watered from the top with a light whisking of water through a very fine rose (sprinkler) on a can.
  5. With smaller seeds, I tend to water the compost before sowing. Or stand the pot in water so it is taken up from below
  6. Seeds that fall or are washed too far down into the compost don't have enough energy reserves to push their first shoot above the surface

Another fault can lie in cooking seeds in un-shaded, heated propagating cases.

Direct sowings follow the same principle. Make shallow drills into firm, not fluffy seedbeds and water the base of the drill during dry weather. Lightly cover the seed and pat down gently over the seeds. Try to avoid watering from the top unless absolutely necessary.

Back to the top

2. I have a shrub that doesn't want to flower.

John Cushnie

Of course, not all shrubs flower! Some shrubs are slower to start flowering than others, but after three to four seasons most species of shrub should be making an effort.

If the plant is sulking and very unhappy with soil or climate conditions, then it may not flower for years until it has become resigned to the conditions.

There are many fertilizers on the market but if you apply a high-nitrogen (N) feed, then the plant will produce extra foliage at the expense of flowers. Feeding with a liquid, high potash (K) fertilizer such as tomato fertilizer will reduce the amount of growth, harden the stems and encourage flowers.

Pruning at the wrong time of the season will result in the flower buds being removed. Plants such as forsythia, flower in spring on shoots produced the previous year and are pruned immediately after flowering. This allows new, young growths to develop that will flower the following year.

Shrubs such as philadelphus, flower in summer on growths made earlier that year. These are again pruned in summer after they have finished flowering.

Back to the top

3. How to tackle invasive weeds.

Bob Flowerdew & Pippa Greenwood

Before you begin, remember the ground surrounding the area you are treating will have much the same weeds. Your priority therefore, is stopping these weed roots spreading back into your plot.

First, dig a perimeter trench around your plot and line this with thick sheet plastic which must come proud of the soil. The trench should be a spade blade wide and as deep as you can manage. Then, you can kill the weeds in the sealed area.

You can do this in a variety of ways:

Method 1: - Turn it over to grass and mow weekly. Just keep mowing whatever is there, Over-sowing with grass seed isn't a must but can sometimes help. Mow repeatedly, returning the clippings, with a nylon line trimmer if not a mower. After two summers the turf can be removed and the soil dug over- though there will be weed roots left to deal with.

Method 2:- Block out the light. In late winter, put a plastic sheet, a woven plastic ground cover sheet, or just layers of cardboard and newspaper over the entire area. If any weeds appear through holes, add a wad of newspaper on top. By the following winter this will be ready to fork over. Alternatively, you could try a thick layer of mulch.

Method 3:- Use a sharpened hoe and cut off every weed to ground level. Repeat every week till they stop coming, then fork over. It may take a few years to achieve the results you need using this method.

As a preventative method, it is well worth cutting the flowers off any weed as soon as they appear, as this will prevent them from forming seeds, thereby reducing their numbers in the future.

For those of you who opt for a chemical solution do not use a cultivator in the infested soil as this will shred the roots and in the process often make the situation much worse. You will often find each section of chopped root will form an entire new plant!

We recommend a non-persistent weed killer. Weed killers based on glyphosate can be taken up by the weeds' foliage and then carried through to all areas of the plant, This chemical is also especially useful as it is inactivated on contact with the soil, so its plant-killing effects will not lurk endure in the soil.

If you do use any chemical weed killer, make sure that the pack label says it is suitable for controlling the weeds you have, and that you follow the instructions to the letter - many weed killers can do untold damage if allowed to contaminate your wanted, garden plants!

Back to the top

4. How do identify my soil type?

Bob Flowerdew

There are six basic types of soil: clay, through to sand, silt, peat, chalk and loam. Everything else is a mix of these.

Some are a gardener's dream (such as a good loam) others need more consideration.

Clay soil: The heaviest clay soils sticks to your boots when wet or even moist.

It will collect pools of water after heavy rain. Clay soil may turn to concrete in hot weather.

Chalk soil: This is a thin soil with many white particles and bits. It usually has chalk not very far underneath. It may stick to your boots when wet but soon dries to a powdery texture when hot. Chalk soil is always alkaline.

Loamy soil: This is generally grainy, easy to dig and only sticks when wet.

Silty soil: This contains particles smaller than sand. It can be acid or alkaline depending on chalky bits.

Peaty soil: This is spongy, dark, with lots of semi-floating bits when mixed in water. It is usually acid.

Stony soil: Any of the above soil types can contain stones. Stones impede cultivation but do no harm to the plants.

pH: If there are little white bits of chalk that fizz if dropped in spirit vinegar then the soil is probably alkaline. If there are no little white bits of chalk then it is likely to be a neutral or acid heavy clay. If there rhododendrons growing around you then your soil it is definitely acid.

If it is reddish, your soil contains plenty of oxidized iron, indicating that it is at least well drained and aerated. If the subsoil is grey and smears. it is anaerobic and needs draining and aerating.

Back to the top

5. How do I keep wood pigeons and other woodland creatures away?

Pippa Greenwood

I'd be fibbing if I said that there was an easy solution to this, but there are things you can do to reduce the negative impact that some wildlife (and certainly wood pigeons) can do in your garden. I find that many vegetables, especially peas and all the brassicas, are often shredded by pigeons. I always protect these using either a net-covered cloche or else pea and bean netting. I drape the fabric over a series of hoops and secure to the ground, fairly taught, using metal tent pegs. Hoops for taller crops such as broccoli or Brussels sprouts are easy and inexpensive to make using a length of old hosepipe (or better still alkathene piping). Drive a length of bamboo cane into each end, then push the canes into the soil so that the pipe or hose forms a sturdy hoop. The same method will also help to keep squirrels off your crops.

Some larger woodland creatures are also deterred by old CDs suspended on twine. Dangle these from the branches of your fruit trees or bushes, or from canes driven in to the soil close to the plants. I find this method especially useful for keeping birds away from fruit trees, and it also seems to help deter deer - the flashes created by both the sun and the moon when their light hits the silver surface works a treat!

And if you're feeling experimental, unwashed human hair tied in to open-weave bags or a section from an old pair of tights, seems to have a useful effect against deer. Tie these 1.5m to 2m (5 to 7 feet) above ground. Human urine (preferably male!) on tree barks also works effectively. Both these methods require regular replenishing, especially after rain.

If rabbits and deer are the main issue, an effective solution is fencing the entire perimeter of the garden, including the gate, with high-tensile stock fencing (minimum height: 1.8m (6ft)), with 2cm hole diameter chicken mesh attached to it (minimum height: 1m (3ft4in). For this to work well you really need to bury the chicken wire mesh 15cm (6in) below ground - making the whole process even more expensive and time-consuming!

For badgers, you should also install 'badger gates' at regular intervals so that they can have free access. If you were tempted not to do this, you can be sure that the badgers will simply make their own way through!

And finally, when all is said and done, remember that the local wildlife and its ancestors probably got there before the houses did, and they do need somewhere to live!

Back to the top

6. How can I get rid of slugs?

Anne Swithinbank

You'll never get rid of them, and in a way we shouldn't try. These slimy molluscs may try the patience of gardeners, but their real job is to eat decaying vegetable matter. They are also the food of many birds and mammals (such as thrushes and hedgehogs).

Slugs are attracted to the soft tissue of seedlings and young plants, so after planting them out, I use slug pellets based on ferric phosphate. These only kill slugs and snails and are considered to be suitable for organic gardeners. Do follow instructions and space them evenly, about 15cm/6in apart. Or, make 'slug pubs' by sinking empty, cleaned margarine or yoghurt tubs into the ground. Leave the rim sticking out, as this will help stop slug-eating ground beetles from falling in. We don't want to kill our allies. Then put enough beer in the tub to drown the slugs.

Some gardeners find barriers effective, as slugs and snails dislike crossing copper (which gives them a mild electric shock), bran, coarse bark or sharp little stone or shell pieces. These are the sorts of barriers you'd use to encircle vulnerable plants like delphiniums in spring.

Slugs that work underground and tunnel into your potatoes are a different challenge. This is where I'd use biological control, which of course also kills young, newly hatched slugs. You can send off for nematodes that are diluted into water and applied through a can with a generous rose (sprinkler) fitted on the end. These microscopic creatures enter and breed inside the slug, while introducing bacteria that infect and kill them.

Snails hide away by daytime and if one of your favourite plants is being stripped of leaves, look around under or behind nearby vegetation. You are likely to be able to pick up a whole colony of snails and solve the problem.

Back to the top

7. Why won't my wisteria flower?

John Cushnie

If it is properly pruned, a grafted wisteria will flower within three years of planting. The secret of success is to build up as much stem with flower buds as possible by pruning. Where there is a mass of growth, then thin some of the stems to prevent the climber becoming congested with a lot of unwanted, whippy growth; as this will prevent sunlight ripening the stems.

Prune the plant in summer, cutting back all the unwanted shoots to within six leaves of the older wood. Allow the main leaders to grow un-pruned but trained in the direction you want them to grow. Shorten back any shoots that grow from the cut branches.

In winter, further reduce the length of the stem to leave 2-3 buds.

It is this wood that will ripen, producing flower buds which open to long, trailing racemes of beautiful wisteria flowers.

During summer, feed regularly with liquid, high potash fertilizer to encourage flower buds and reduce the overall vigour of the climber.

Back to the top

8. Please can you suggest some plants for a shady garden?

Matt Biggs

Many species and cultivars of plants able to flower in the shade, bloom in spring before leaves appear on the trees. These are therefore useful under deciduous trees or shrubs. 'Snowdrops' (Galanthus sp.), 'Dog Tooth Violets' (Erythronium sp) including Erythronium 'Pagoda' with dainty yellow flowers, 'Wake Robin' (Trillium sp.) and 'Arisaema' (Arisaema sp) are ideal in these conditions and 'Periwinkles' (Vinca) make good ground cover

Shrubs such as Rhododendrons, Hydrangeas and Mahonia Ivy, Hostas and ferns add coloured foliage and increase the season of interest. It is important to add plenty of well-rotted organic matter, like homemade compost to the soil and allowing it to settle before planting.

Plants suited to dry shade include Omphalodes cappadocica 'Cherry Ingram', Geranium phaeum the 'Mourning Widow' geranium with dark purple flowers and the white form, 'Album', Euphorbia amygdaloides var. 'robbiae', a spreading Euphorbia with lime green flowers in spring, creeping 'Dead Nettle' like Lamium galeobdolon 'Hermann's Pride' with yellow flowers and white patterning on the leaves, Brunnera macropyhlla 'Jack Frost' with fabulous silvered leaves and Hellebores such as Helleborus foetidus 'Wester Flisk Group' with remarkable red tinted stems and architectural leaves. Epimediums such as evergreen Epimedium alpinum are irresistible, too. Among the ferns are male (Dryopteris filix-mas), golden scale (Dryopteris affinis), soft shield (Polystichum setiferum) and hard shield (Polystichum aculeatum) and 'Hart's Tongue' fern, (Asplenium scolopendrium).

Bedding plants like Fuchsia, 'Bizzy Lizzy', Begonias and Lobelia grow happily in shade; choose white flowered cultivars which show up well in low light.

Back to the top

9. Which plants will add fragrance to my garden?

John Cushnie

There are so many and even in winter there will be a constant supply of perfume.

In spring hyacinth bulbs will fill the air with a heady fragrance. Rhododendron luteum, the deciduous azalea with sulphur yellow flowers will add its perfume in late spring. For summer you can rely on sweet pea, roses, lavender and lilies. In the late summer evening, Nicotiana sylvestris (tobacco plant) Night scented stock and Evening primrose will take over filling the night air with scent.

For winter, you must plant the Christmas box (Sarcococca confusa). It is an evergreen shrub with tiny white flowers that in the dead of winter exude an incredible fragrance. If you are within seven metres (eight yards) you will know it. The witch hazel, Hamamelis flowers in winter producing its perfume from small, spider-like yellow flowers on the bare branches. In late winter the daphnes such as D.mezereum take over dishing out scent. Overhead the vigorous, evergreen, climbing clematis C.armandii will drizzle down its almond perfume from the white flowers.

Back to the top

10. How do I control potato blight?

Matt Biggs

Potato blight is becoming a major problem in damp summers. Brown or black patches appear on the tips and margins of leaflets of potatoes, which then curl up and wither. The disease then spreads rapidly to leaves and stems then finally the plant collapses. Spores are washed down to the tubers, they become discoloured and a reddish-brown rot appears, this, alongside other infections, reduces the tuber to a stinking, liquefied mass. Potato blight is devastating, destroying crops in the ground or when infected tubers are stored.

Spores are spread by wind and rain in warm humid conditions, usually from mid-July onwards, when temperatures exceed 10oC (50oF). You can also buy a home testing kit to check signs of infection. Remove infected foliage immediately to slow its spread and prevent spores spreading to the tubers. Tuber infection can be reduced by 'earthing up' or mulching with a thick layer of organic material like hay or straw.

Buy healthy seed potatoes from a reliable source. Keep your plot clear of rotting and infected debris and plant alternate rows of resistant varieties. Avoid sheltered sites and widen the spaces in and between rows. Position these rows into the prevailing wind or in exposed areas, for greater air movement. Dry, sunny weather stops blight from spreading, so it is not a problem in hot, dry weather. Check stored tubers regularly and remove any showing signs of rot.

To reduce problems, plant early varieties which mature before blight appears, then save some to plant later in summer after the disease has peaked. Look out for early signs of blight in neighbours' gardens and local fields, then apply preventative sprays of 'Bordeaux mixture' or a similar copper based fungicide, before it arrives. Early warnings of blight infection or a 'Smith Period' are often broadcast on local farming programmes, Farming Today on BBC Radio 4 or can be found on (registration required). Do not leave blighted tubers in the soil; lift every one and dispose of them away from the garden.

Potato varieties showing some resistance to blight, include 'Colleen', 'Premiere', 'Cosmos', 'Lady Balfour', 'Pomeroy', 'Orla', 'Remarka', 'Cara', 'Milva', 'Valor', 'Verity' and 'Arran Victory'. 'Sarpo' varieties like Mira' and 'Axona' are among the most resistant varieties available. Even some of the 'resistant' varieties may be attacked in years when potato blight is severe.

Back to the top

Last On

Gardeners' Question Time

Available to listen


Peter Gibbs hosts the horticultural panel programme from Shrewsbury.

Coming Up

Gardeners' Question Time


Eric Robson hosts the horticultural panel programme from Bradford-on-Avon.


[an error occurred while processing this directive]

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.