Thompson & Morgan Facebook Q&A Session 19th October 2012 - Your horticultural questions answered.

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Name: Barbara Hyde

Question:Please could you let me know what might be happening to my raspberry canes. These are an Autumn variety I bought from you last Summer. They produced beautiful fruit the first year and then this autumn they look like this. Any idea whether it is some sort of deficiency or a virus or what. I would be very grateful to know what you suggest I feed them or spray them with. Thank you so much.

Answer: Hello Barbara. There are several likely causes of the yellow blotching that you can see on the leaves of your raspberries. It is possible that your plants have become virused. Viruses are usually introduced to a plant by a vector such as aphids or soil dwelling nematodes and tend to cause a reduction in crop yield as well as some stunting of the plants growth. These symptoms tend to become more pronounced over time.

However, similar yellow blotching can also be caused by the Raspberry Leaf and Bud Mite, Phyllocoptes gracilis, which is far less damaging, but will cause a reduced crop, and often slightly crumbly fruits. Raspberry Leaf and Bud Mite is a microscopic, yet widespread pest. You won’t be able to see it with the naked eye. Although they are active from April onwards, the damage tends to become most apparent in late summer and autumn, particularly if the plants are being grown in a sheltered position or during a hot summer.

The advantage of having Autumn fruiting raspberries is that this type of cane can be cut back to ground level in February each year, thus breaking the lifecycle of the bug which overwinters on dormant canes. Burning the prunings should be sufficient to control the problem. I would suggest that you try this first. Give the plants a really good mulch of well rotted manure after pruning to encourage plenty of strong new growth. You can also give them a feed of blood, fish and bone in spring which will certainly help them along.

If the problem recurs next year, then you may be dealing with a virus. Virused plants are best destroyed and new ones replanted in a different position in the garden. Always burn infected plant material rather than composting it. Hopefully a good pruning and a feed will solve the problem for you.

Name: Apie En Michelle Pieterse

Question: Hello. What would you suggest I could do to cover an ugly exterior wall as quickly as possible over the next year or two? Something fast growing, evergreen and attractive.An Ivy variety perhaps? Thanks you, I am an absolute useless gardener, but going to make it a priority in our new home...massive garden and lots if potential! Also...is now a good time to be planting lavender at all or should I wait until next year?

Answer: You could certainly use ivy – there are some very nice varieties available that would provide dense cover once established. Bear in mind that many of the variegated varieties need good light for the best colouring.

Perhaps you could try evergreen Lonicera japonica ‘Halliana’ (Japanese Honeysuckle) which has sweetly scented flowers in the spring and summer. Pileostegia viburnoides is another attractive evergreen climber with heads of small cream flowers in late summer and autumn. You might even want to consider an evergreen wall shrub such as Pyracantha which will provide both summer flowers and colourful autumn berries - although bear in mind it does have woody thorns.

Some of my favourite evergreen climbers come from the clematis family. Try Clematis armandii which has very vigorous growth, or the beautiful Clematis ‘Winter Beauty’. I think my first choice would have to be Clematis ‘Freckles’ for it’s gorgeous, pink winter flowers and fluffy seedheads. There are lots of choices, but hopefully this gives you some ideas.

Regarding your lavender, I would be inclined to wait until the spring before you plant them out. This gives them a better chance of establishing before they have to face a cold winter. It’s also worth noting that English lavender tends to be a bit tougher than French lavender. However, if you don’t have any plants yet then it would be worth buying your plugs now and growing them on in a cold greenhouse overwinter. This way they will be ready for planting in spring. Go for a tried and tested variety such as Lavender ‘Hidcote’.

Name: Steve Smith

Question: How do you over winter that hardy gerbera? We're struggling on finding much about them. Do you leave the foliage or do you cut them back? Many thanks.

Answer: Hi Steve. In mild parts of the UK, Gerbera ‘Forever Daisies’ are reasonably hardy outdoors, if grown in a sheltered position and provided with winter protection during particularly cold periods. In cold areas it is preferable to grow gerbera plants in containers that can be moved to a frost free position during winter.

If your plants are in containers then a cold greenhouse should provide adequate protection in winter. Just reduce watering to keep the compost barely moist throughout the coldest months as wet soil may cause them to rot off. Outdoors, I would allow them to die back naturally, like any other perennial, before clearing away the old foliage. It would be worth applying a dry mulch of bark chips or straw just to protect them from the worst of the weather. Best of luck, Steve.

Name: Craig Mason

Question: What’s the best tasting tomato to grow in an unheated greenhouse. Thinking what to grow in 2013.

Answer: That’s a tricky question Craig – there are so many to choose from! Our most popular variety is Tomato ‘Sungold’ which has to be one of the sweetest varieties available. Its red sister variety, Tomato ‘Suncherry Premium’ is equally tasty. If you are looking for a larger tomato then try the beefsteak variety Tomato ‘Brandywine’. It’s a heritage variety that’s well worth growing for its rich, complex flavour. I suppose it’s all about personal taste really, and some people prefer a more acidic flavour while others like a sweeter tomato - but ‘Sungold’ is definitely a good choice to start with.

Name:Pauline Lloyd

Question: When should I plant Dutch Iris bulbs? I'm finding info that says now others that say from Jan-March. Feeling overwhelmed as I have loads of bulbs and all needing different things!! Help!

Answer: Hi Pauline. Don’t get too worried about this. In an ideal world you would plant them now, but they can still be planted over the next few months if that’s more convenient, just so long as the soil is not waterlogged or frozen. Plant Iris reticulata bulbs at a depth of approximately twice their own height. Choose a position in full sun in moist, free draining soil. To create a natural effect, you can try casting the bulbs across the planting area and plant them where they land. Alternatively, plant your Dutch Iris bulbs in deep containers of loam based compost such as John Innes No. 2 and grow them on in a greenhouse or a cool sunny windowsill for an early indoor display.

After flowering, allow their foliage to die back naturally before removing it in order to feed the bulb for the following spring. Divide overcrowded clumps of dwarf iris bulbs in autumn. Keep pots of iris reticulata just moist during their dormant period and gradually increase watering as again growth begins in spring. I hope that helps you Pauline

Name: Kevin Joseph

Question: Question for sue: I have 2 three year old bamboos (phyllostachys aurea) and I’m getting slightly worried that the roots may get into the foundations of my house. Do they spread that much?

Answer:Hi Kevin. That’s a spectacular clump of bamboo in your photograph! You haven’t mentioned how far it is growing from your house, but as it’s a clump forming variety then I don’t think you need to worry too much.

The main concern about growing plants too close to buildings comes from the risk of subsidence. However this is only really a problem on clay soils, and such cases generally tend to involve mature trees and larger shrubs that have a much higher water use. Having said that, I do recall a case where subsidence was attributed to a particularly vigorous Japanese knotweed problem, so these things are not unheard of. If you have noticed cracks forming in your walls and ceilings, then you should call your buildings insurer and discuss the matter with them.

There’s nothing to stop you digging out some of the bamboo closest to the house from time to time - just to keep it under control. Be warned that this will take you a long time and is quite hard work as Bamboo roots are pretty tough. You will probably need an old saw to cut through the roots too. Best of luck Kevin. Btw: How’s that Camellia looking these days?

Name: Pauline Irvine

Question: Looking for some help... MY Arum Lily flowered this year for the 1st time after 4 years and now has some seed pods on it. What do I do with them? Novice at this one.

Answer: Good to see that it has finally flowered for you, Pauline. You have a simple choice to make – either cut the seed heads off, or leave them on and let the plant set seed.

You don’t mention what species this Arum is, so I can’t tell you whether the seeds are likely to germinate in your garden or not. But if you like the plant and you want it to spread, why not leave it to its own devices? Once the seeds have dropped, the plant will die back naturally and you can remove the old stems and foliage to make way for new growth in spring.

Keep an eye out for seedlings in spring around the base of the main plant. You can either leave these in situ or gently lift them and move them to other areas of the garden. If you find that it is taking over the garden in future years then simply removing the seed heads will restrict its spread.

Name: Jackie Mason

Question: Help please with my Heuchera Caramel. Photo attached - is this a disease or insect? Any thoughts. Jackie

Answer: Hi Jackie. It looks as though your Heuchera is suffering from a strain of fungal leaf spot. If you can see raised orange pustules when you look at the underside of the leaf then it could even be Heuchera rust. There are many different fungi that can cause this spotting, which tends to occur during cool, wet weather, or where plants are watered from above the foliage. Plants that are fed with high nitrogen feeds and grown tightly together (thereby reducing ventilation) are also particularly susceptible. Although Heuchera is normally fairly disease free, it is worth noting that the yellow, orange and bronze coloured varieties tend to be more susceptible.

The wet summer and damp autumn weather will have created ideal conditions for the spread of fungal spores. Remove and destroy any affected foliage that you can see and spray the new growth with a fungicide that is suitable for use on ornamental plants to try to restrict the problem from spreading. I would also recommend that you clear away any fallen plant debris from around the plant and burn it to prevent overwintering spores from reinfecting the plant next year. Hope that helps Jackie.

Name: Sarah Griffiths

Question: Hi, have a question for Sue. My lawn is covered in small piles of dirt - someone mentioned worm casts (?) to me - are these good for my lawn? thanks.

Answer: Hi Sarah. Worm activity in lawns is a common problem particularly in autumn and winter when the soil is wet...although their presence does also indicate that your soil is in quite a healthy condition! The casts are the main problem as they look unsightly and can cause muddy conditions when they are stepped on. A high level of worm activity can also attract moles which feed on worms. Whilst they are unsightly and can be messy if the lawn is walked across, they won’t actually damage your lawn.

There are a few things that you can do to discourage them. Worms prefer a neutral to alkaline soil pH. The pH can be lowered by adding fertilisers which contains sulphate of iron. Sulphate of iron will make the lawn surface more acidic and discourage worms. Worms enjoy feeding on organic matter in lawns, often referred to as ‘thatch’, which can be caused by moss and old grass clippings. Make sure that you remove clippings when you cut the grass and rake up fallen leaves in autumn to reduce the accumulation of thatch. Scarifying your lawn will also help to reduce thatch.

The worm casts can removed by sweeping them off the lawn if necessary, but make sure that they are dry before you start this task, otherwise they will just smear across the grass.