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Facebook Q&A Session 10th August 2012


Thompson & Morgan Facebook Q&A Session 10th August 2012 - Your horticultural questions answered.

Click here to view details of our previous Q&A sessions.

Name: Anna Simon

Question: I am growing butternut squash and they are doing well with lots of tiny fruit on each plant. Do I need to do anything to them such as limit the number of squash that develop on each plant or should I just leave them to it? And do I do the same to the pumpkins that my children are growing? Thank you, Anna.

Answer: Hi Anna. With Pumpkins it really depends on what size fruit you want. If larger fruits are required, then you should remove all the fruits except for about three per plant. This diverts all of the plants energy into growing fewer but larger fruits, which is ideal if they are being grown for carving at Halloween.

In principle, the same applies to squash plants, but as they are generally grown as an edible crop then it’s preferable to grow smaller fruits in larger numbers. Therefore thinning should not really be necessary. It’s great to hear that your plants are doing well. It sounds like you are going to have a bumper crop this year!

Name: Di Hobbs

Question: What can I plant in a heavy clay soil that’s long lasting, blue or purple flowering and most importantly SLUGS not attracted to them at all, thanks.

Answer: Hello Di. It seems as though there is very little that hasn’t been eaten by slugs this year, but don’t despair - there are a few species that don’t seem to be quite so prone to slugs and snails. If your soil is really very heavy then it would be worth improving it with some well rotted manure or other organic matter to break it up and encourage better drainage. This will significantly broaden the range of plants that you can choose from.

Have you tried growing hardy geraniums? They will cope on most soils and there are plenty of blue and purple flowering varieties to choose from. Try a fairly vigorous variety such as Geranium ‘Rozanne’ or G. pratense ‘Midnight Blues’.

Aconitum is also fairly slug resistant and will generally cope on clay soils, although it isn’t particularly long flowering. You should also be aware that all parts of this plant are toxic, although this will only really be a problem if you have small children about.

Plants with prickly or hairy foliage/ stems are also fairly slug resistant. Try Pulmonaria, Stachys, or Rose ‘Blue for You. Vinca minor and Ferns are also quite good in clay soil and not particularly appealing to slugs. You will also find that Astilbe and Japanese anemones are fairly slug free. You won’t find blue varieties but there are some nice white forms that are worth trying.

Remember that the more mature and better established a plant is then the more resistant to slug attack it will be. With this in mind, it is well worth planting perennials from a 2 litre pot size as these will be better equipped to outgrow any damage that is sustained. I would also use slug pellets, at least while the plants are establishing, to give them a fighting chance. I hope that gives you a few ideas Di. Best of luck.

Name: Paul Britton

Question: I've sown Penstemon hetrophyllus 'True Blue' & 'Miniature Bells Mixed' in a clear, unheated propagator, in multipurpose compost, covered with vermiculite, and kept them moist. They were both sown on the 12th June, but no show as yet other than a type of green lichen attached to the vermiculite. I've had to water as the cells appear to dry out quickly & I know that they can take up to 4 months to germinate, but I don't know if I've drowned the seeds or if they are just still in a dormant state. What I would like to know is if I should just be patient for another 8 - 10 weeks, or just empty out onto the compost heap & restart the process when the time arrives, but using a type of John Innes seed & cutting compost instead, or forget the seeds & buy plug plants from yourselves.

Answer: Hi Paul. I have had problems with Penstemons myself so I can understand your frustration. The problem is that they take a long time to get going and in the meantime you need to keep the compost moist without it becoming over wet or too dry - which can be tricky! It may be worth hanging on to the modules just in case something comes up but, to be honest, if there is lichen now growing on the vermiculate then this would suggest that the compost is a bit wet and the seeds have probably rotted off.

I would suggest resowing using a proper seed sowing compost. Water the compost before sowing and cover the seed lightly with vermiculite. It might be worth investing in a heated propagator as this will provide warmer soil conditions. Hopefully the seed will germinate much quicker, giving them less opportunity to rot. When the soil begins to dry out (this will happen more frequently if you are using a heated propagator), you can water the modules by standing them in a shallow container of water. Watering from below is less likely to rot the seeds. As soon as the surface of the compost starts to become moist, remove the modules from the watering container and let the pots drain thoroughly before returning them to the propagator.

Watering from below is a much safer method when dealing with little seeds like Penstmons. Even after germination I would recommend continuing this method, at least until after ‘pricking out’. Also don’t be in a hurry to prick the seedlings out, as they are quite slow to produce a decent root system. I hope you have better luck next time. I must admit that it took me a few tries to get it right.

Name: Jackie Mason

Question: Hi, my vegetables are disappointing - very few mange touts, courgettes slow, radishes not swelling, etc. Any ideas for the rest of the season? And I have only 7 flowers on the runner beans, and very little green growth!!

Answer: Hi Jackie. Don’t be too disheartened - it has been an appalling year for many gardeners and crop production has been well below normal expectations. The cold, wet weather has had a big effect on many people’s gardens and made plant growth very slow. Unfortunately there is very little that you can do about it.

Leave the plants in the ground for now. There is still time for crops to be produced but don’t expect too much. If you have any vegetables growing in containers then these can be moved to a greenhouse to provide more heat, which should speed up growth a bit. In these circumstances the best thing to do is to right it off as a bad year and hope that next year will bring a better growing season.

Name: Samantha Jane Ward-Evangelista

Question: Why has my plum tree planted in a pot got yellowing leaves?

Answer: Hi Samantha. It sounds as though your plum tree is struggling a bit. Yellowing leaves are often an indicator that some improvement is needed in the plants growing conditions. If you have had the tree growing in a pot for a while then it may be pot bound or have run out of nutrients.

Remove it from the pot and check to see whether the roots are congested. If so, then a larger pot is required. Gently loosen the roots with your fingers and repot the plum into its new home. Don’t be tempted to use ordinary multipurpose compost as this will quickly lose its structure, becoming poorly aerated, prone to waterlogging in winter and drying out in summer. Use decent quality compost instead, such as John Innes No. 3.

Your tree may also need a feed. Use a soluble fertiliser throughout the growing season to keep your plant well fed. Remember that when a plant is grown in a container it is entirely reliant upon you to provide any nutrients that it needs. The same applies to watering. Try to keep the compost evenly moist with regular watering whenever required.

If you improve the growing conditions of your tree then you should see an improvement in leaf colour with time. If not, then there may be a different problem, but at least you will have ruled out the basics. I hope that helps Samantha.

Name: Lerone Stanton

Question: The growing shoot of my lilly bulb was eaten by snails earlier this year. I haven't seen any growth since then; will it come back next year?

Answer: Hi Lerone. That’s a great shame. Slugs and snails have caused no end of damage this year. Unfortunately I can’t guarantee that you will see any growth next year as the plant has not produced the leafy growth that is needed to feed the bulb for next year’s display. It might be worth lifting the bulb in autumn to check that it is still firm and hasn’t rotted off. If it looks ok then hang on to it and see what happens in the spring - but I wouldn’t expect too much from it.

Name: Lucy Garden

Question: Hi, Sue, I love viburnums and have several sorts in the garden. Do they hybridise? I was thinking of collecting the seed from one of them and seeing what comes up in case I get some interesting crosses. What do you think? My "plicatum Mariesii" (or similar) has lots of berries this year...

Answer: Hi Lucy. Viburnum can be hybridised so it’s always worth a try. However it will be quite a few years before you actually see the fruits of your labour! If you are interested in having a go then it would be best to select particular flowers from specific parent plants before they open and cover them with a bag to prevent insect pollination. Once opened, you can try hand pollinating them. When you have pollinated the flowers you will need to mark them with a piece of thread or wool so that you can identify which seed heads to collect later in the season. By hand pollinating, you will at least know what the parentage is of any offspring that you raise. Best of luck Lucy.

Name: Jane Grindrod

Question: Help! The tree lillies I bought were doing really well until the leaves fell off and they began to droop. I put this down to a crummy Summer but a friend of mine informed me that the cause was the pesky red lily beetles. How do I get rid of them? Or is it worth giving them up as a bad job this year and trimming them down? Also, how do I stop this repeating next year? Is it a case of re-potting them? I'm gutted, was so looking forward to them this year. x

Answer: Hello Jane. Lily beetle tend to cause a lot of damage to the foliage and can make a real mess of your plants by chewing the leaves and buds - but I wouldn’t expect them to cause the plant to drop its leaves or wilt. Of course it is quite possible that your lilies are also suffering from lily beetle, but this sounds more like a problem with the bulb to me.

My guess would be that the bulb may have started to rot for some reason. The most obvious cause would be if it has been sitting in wet soil over a long period. If you are growing your lily in a container then it is possible that the drainage holes are blocked, or maybe it has just been over watered. Rot can also set in if the bulb has been damaged somehow - this can sometimes happen if you stake the flowers after planting and accidentally push the stake through the bulb.

I think that it would be worth investigating what’s going on beneath the soil. Gently scrape back the soil to reveal some of the bulb and see if it is still nice and firm. Any indications of squishiness will confirm that rot has set in, and it is best discarded.

Regarding Lily Beetle, this pest is best controlled by removing and crushing any larvae or adults that you see. Check for the underside of leaves as they can often be found lurking there. You will need to inspect your plants throughout the growing season to keep on top of the problem. If you have a severe infestation then you may need to use an insecticide such as Bayer Provado Ultimate Bug Killer or Scotts Bug Clear Ultra. I hope that helps Jane.

Name: Clare Rushton

Question: Any idea what has happened to my apple tree? The apples are all looking scabby and the leaves are going yellow with black spots and dropping off. What can I do?

Answer: Hi Clare. My first thought from your picture was that this was some kind of russetting. This can be caused by nutrient deficiencies in the soil, or if the young fruits are affected by a late frost. There is normally no need to worry about this and the fruit should be edible still, although you may prefer to peel the skin. You can improve the soil conditions in autumn by aerating the ground around the root zone and spreading a thick mulch of organic matter such as well rotted manure to improve soil fertility. Russetting can also be caused by the fungal disease powdery mildew which can normally be spotted as a white powdery substance on the upper surface of the leaves. It might be worth checking for signs of this.

My other thought is that the tree may be suffering from Apple scab, particularly as the leaves are showing black spots and dropping. This is a fungal disease that commonly spreads during wet weather. Once again, the apples should be perfectly edible beneath the skin.

Where any fungal disease is involved, the best method of control is to clear up any fallen leaves that may be infected with spores and destroy them on a bonfire - don’t add them to the compost heap. This will help to prevent the spores overwintering and re-infecting your tree next year. There are fungicides available that can be used on fruit trees but I would be cautious now that your fruits are maturing. You may want to harvest your crop first. Hopefully, we will have a drier summer next year and this problem will resolve itself.