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Facebook Q&A Session 27th June 2014

Thompson & Morgan Facebook Q&A; Session 27th June 2014
- Your horticultural questions answered.

Our horticultural expert Sue Sanderson runs a fortnightly question and answer session - so if there is something that has been eluding you in your garden, post your question on our facebook page and she will get back to you during her next Q&A; session.

View the answers to our previous sessions.

  • Megan Cotterill
  • Why do the leaves on my camellia bush turn yellow after flowering? I have three bushes in the garden but it only happens to one of them.

  • Sue - T&M; Horticultural Expert
    Sue Sanderson - T & M Horticulturalist
  • There are lots of reasons why Camellia leaves turn yellow and there is often a pattern to this yellowing that will help you to determine the problem. If the yellow leaves are predominantly situated towards the bottom or the centre of the plant then this is likely to be perfectly normal. Older leaves are naturally shed in spring and summer as the plant grows.

    However if you are spotting yellow or yellow-white speckled or blotchy areas on individual leaves then this may be an indication that the plant has Camellia Yellow Mottle Virus. It tends to be confined to individual branches which can easily be pruned out. There is no chemical control for this virus but it doesn’t really harm the plant particularly and may even disappear with time.

    Nutrient deficiency is often to blame for yellowing foliage. Camellias enjoy acid soil, so when planted in a more alkaline soil they may show symptoms of iron and manganese deficiency. In this case, the yellowing will show between the veins of each leaf. In alkaline soils, Camellias are best grown in containers of ericaceous compost and watered with rainwater rather than tap water (tap water contains lime which will turn the soil alkaline over time). It’s possible that the variety which is turning yellow is more sensitive to soil pH than your other plants, or that the soil is more alkaline in the particular area in which it is growing.

    Without seeing the plant in question it is hard to be specific, but hopefully this will give you a few ideas as to what the cause might be.

  • Sophie Hall
  • Hi, I’ve been at my allotment only to discover most of my raspberry crop covered in grey mould. I understand that better ventilation around the plants might help next time, but is there anything I can do to save any of this year’s crops please? Also am I safe to leave the existing canes in for next year or should I replace/relocate them. Any help would be much appreciated.

  • Sue - T&M; Horticultural Expert
    Sue Sanderson - T & M Horticulturalist
  • Hello Sophie. What a shame that your crop has been affected. Grey Mould is a real nuisance, particularly during periods of humid weather. It often infects the plant through the flowers and is not obvious until the berries begin to ripen. At this point the berries begin to rot and the fungus is clearly visible on the fruits.

    Unfortunately, there are no approved fungicides available to gardeners that will control Botrytis cinerea. This fungal disease is airborne and therefore there is little that you can do to prevent an outbreak from occurring apart from increasing air movement around the plants as you have already mentioned.

    The spores survive in dead plant material, so it is very important to be scrupulous about clearing away dead and dying plant material and disposing of it on the bonfire. You should also remove the infected fruits to restrict its spread.

    It may be beneficial to thin out the stems of your plants in future years to allow improved airflow around the plants. There is no need to relocate them, however if they are terribly crowded together then it might be worth lifting them this winter while they are dormant and replanting them at a greater distance apart. I hope you have better luck with your Raspberries next year.

  • Sue - T&M; Horticultural Expert
    Sue Sanderson - T & M Horticulturalist
  • Horse tail or mares tail (Equisetum arvense) is such a nuisance! This weed has been around for millions of years and its roots can extend to more than 1.5m deep into the ground. It’s a really tough plant that can re-grow from the smallest piece of root. Whatever you do, please don’t rotavate the area as you will only spread the plant further still.

    Cut back as much as you can at ground level and when the new growth emerges use a glyphosate based herbicide such as ‘Roundup’ to kill it off; but be warned that you may need to make up to 5 applications before it shows signs of weakening. Keep on top of the problem and spray new growth as soon as it appears, before it reaches 7cm (3") high. Many people suggest that crushing the stems first will improve the results. I have never tried this myself, but it might be worth a go. The idea is to starve the root until it dies, but it will take a lot of persistence on your part. Good luck Carol.

  • Vida Maria Hills
  • Why are my sweet peas turning yellow and dying long before they should?

  • Sue - T&M; Horticultural Expert
    Sue Sanderson - T & M Horticulturalist
  • Hello Vida. There are a few possible reasons for this, but it’s always very difficult to diagnose the problem without seeing the plant. Sweet Peas can show signs of yellowing if they experience significant dryness at the roots. Likewise, overwatering can cause similar yellowing of the leaves. Try to keep them evenly moist throughout the growing season to prevent this from happening.

    Have you been feeding them regularly? Sweet Peas are quite hungry plants and will appreciate a regular liquid feed every few weeks. Yellowing can sometimes occur if there is a magnesium deficiency, but a general purpose feed ought to put this right. They enjoy a rich, well drained soil that has been improved with plenty of well rotted manure prior to planting - this is well worth doing in future years, particularly if you are gardening on light sandy soil.

    The only other thing that I can think of is that they could be suffering from Leaf Scorch which gradually gives the plants a white, scorched and dried out appearance as they slowly die off. Sweet Peas are particularly susceptible to this especially when grown on light soils. It tends to start on the lowest leaves first and then spreads to the rest of the plant. Leaf scorch is generally associated with temperature stress and/ or periods of drought. There’s not much that you can do except for keeping them consistently moist and avoid watering from above. I hope that something here sounds familiar and that you have better luck with your Sweet Peas next time.

  • De Hooge Henny
  • Was given a Lily plant for Mothers Day, which had loads of buds but most of them fell off. However I did end up with about 6 beautiful open flowers. Then about 4 weeks ago it was attacked by the Lily beetle. I caught 5 of the little pains. Touch wood, they didn't come back. But what can I do with the leaves what where attacked and now have turned brown. Can I cut the tops of?

  • Sue - T&M; Horticultural Expert
    Sue Sanderson - T & M Horticulturalist
  • Hello De Hooge Henny. Lily Beetle can cause a lot of damage very quickly! The larvae do more damage than the adult beetles. Remove and crush 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.

    You can certainly remove the brown leaves as they won’t be of any benefit to the plant once they deteriorate to this condition. I would be inclined to leave the tops on the plant and allow them to die back naturally as this will help to feed the bulb in preparation for next year.

  • Sherry Irvine Mills
  • Best way to deal with hydrangeas? Soil, location and pruning. And how to take cuttings please?

  • Sue - T&M; Horticultural Expert
    Sue Sanderson - T & M Horticulturalist
  • Hi Sherry. Hydrangeas are one of my favourite plant groups. There are some really lovely varieties available at the moment including the 2014 Chelsea Plant of the Year Winner Hydrangea macrophylla ‘Miss Saori’.

    I have recently written an article on ‘How to grow Hydrangeas’ which will explain how to care for Hydrangeas, including pruning.

    With regards to taking cuttings, you can take soft wood cuttings now and root them in now. Take cuttings from non-flowering shoots that are around 10cm (4") long and cut them just below a leaf node. You will need to reduce the leaf area by removing the bottom few leaves. Dip the bottom into rooting hormone powder and stick them around the edge of pots of free draining compost. You should be able to fit several cuttings in each pot. If you can provide a little bottom heat to get them rooted in then this will help. They will need to be kept in well ventilated, frost free conditions over winter. A heated greenhouse would be ideal. Best of luck with your cuttings Sherry.