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Facebook Q&A Session 23rd August 2013


Thompson & Morgan Facebook Q&A Session 23rd August 2013 - Your horticultural questions answered.

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Name: Lesley Gilbert

Question: I have noticed quite a significant problem this year with my runner bean flowers not setting. I noted on the RHS website that often this is due to bees not pollinating in the usual way and getting to the nectar without actually going inside the flower! I watched on my plants and almost all of them do exactly that - any thoughts? Thx Lesley

Answer: Hi Lesley, this is a bit of a nuisance but unfortunately there isn’t much you can do about the bees biting holes in the flowers. The only solution is to try growing self-setting varieties of bean which don’t require a pollinator, such as 'Firestorm', 'Snowstorm' or 'Moonlight'. I hope this helps, best of luck with your future crops.

Name: Ian Woodhams

Question: When feeding container plants, how much of the feed should be applied when using a concentrated mix? A good soaking until mixture starts to run through drainage holes or just a light application? The only advice I've ever read is how to mix the concentrate correctly, not how much to apply. Thanks in advance.

Answer: Hi Ian, the dosage recommended on the box is aimed at watering your plants as per normal - I normally allow about an inch or two of water to accumulate on the compost surface for each pot. It’s best to apply fertiliser to slightly damp compost otherwise it will run straight through the pot and be wasted. I hope this helps.

Name: Sharn Louise Gray Jones

Question: I really like growing cabbages and kale, especially "walking stick". I've never managed to grow them to 2m high though! My problem is pests eating them too quickly - I don't use any insecticides at all as I keep animals near, are there any "natural" spray remedies?

Answer: Hi Sharn, I know how frustrating pests can be on cabbage crops! The main culprits are cabbage white caterpillars and slugs. If you prefer to grow your vegetables organically then you can pick the caterpillars off by hand and crush the clusters of small yellow eggs on the underside of the leaves. Make sure you check the plants regularly as the butterflies will lay eggs throughout the summer. You can also use nematodes, small parasitic worms which you spray on to the caterpillars. The nematodes infect the caterpillars and kill them. It is perfectly safe to use on edible crops and is harmless to children, pets and wildlife. They are available online and in most good garden centres. I have found the best method of control is to net all my Brassicas with a fine mesh, preventing the butterflies accessing them! Make sure you use a mesh with holes no bigger than 7mm - it’s surprising how the butterflies can squeeze into even the smallest gaps. Secure the mesh to a frame and seal it at the bottom with pegs, bricks or a long wooden bar. I’ve found netting very effective and a lot easier than picking the caterpillars off by hand each week.

For slugs you can buy organic pellets made from sheep’s wool which create a layer of fibres on the soil surface, which they find irritating so won’t cross. You can try picking the slugs off the leaves and stems at dusk when they are at their most active. Although this can seem laborious it is very effective. There are also nematodes for slugs which you water into the soil. Alternatively try placing empty grapefruit skins or melon skins upside down on the soil. Slugs love to gorge on the sweet, aromatic flesh of fruit and the darkness and moisture suits them well. All you have to do is check the skins each morning and destroy the slugs hiding in there! I hope this helps Sharn, best of luck.

Name: Wakki Jakki

Question: Any good tips on growing rhododendrons from cuttings..? They fail every time I try.

Answer: Hi Wakki Jakki, Rhododendrons are more difficult to root than many shrubs and are best taken with a ‘heel’, and wounded to encourage rooting. A heel cutting is simply where new growth is pulled away from the main stem with a small heel of bark still attached. The heel contains concentrated amounts of growth hormones which are needed for rooting to occur. They can be taken as semi-ripe cuttings between late July and October so you would be fine to try this now. Semi-ripe cuttings should be taken from the current season’s growth and should have a fairly hard base and a soft top. Fill pots loosely with a mixture of 50% compost and 50% perlite for good drainage. Gently pull away the plant material and trim the heel. Remove the leaves on the lower third of the shoot and cut any remaining big leaves in half to reduce water loss. Dip the base of the cutting into hormone rooting powder to encourage rooting and protect from rotting. Insert the cuttings around the edge of the pots, spacing them so the leaves aren’t touching. Water well and allow the pots to drain before placing inside a clear plastic bag. Keep the pots somewhere warm and bright but out of direct sunlight if possible. Make sure the compost remains moist. After 6-8 weeks you should start to see roots appearing out of the drainage holes, at which point your Rhododendron cuttings can be potted on. I hope this helps, good luck.

Name: Alan Humphreys

Question: My Lupins keep getting like a white coating on their leaves. Any ideas what it is and what I can do to prevent it?

Answer: Hi Alan, powdery mildew is quite prevalent at this time of year and affects a wide range of plants. It is often associated with humid conditions and the plant becoming dry at the roots. Unfortunately Lupins are particularly susceptible, but it can be controlled by spraying with a fungicide. There are lots available, just check the manufacturers label to make sure you choose one that is suitable for clearing powdery mildew on ornamental plants.

To prevent further outbreaks I would suggest keeping your plants well watered (try to water them at the roots and not from above as this is likely to spread the spores). Cut out any heavily infected shoots and burn them. In autumn, remember to clear any neighbouring plant debris away from the area as this is likely to harbour over-wintering mildew spores. And finally, try to maintain good air circulation around the plants by keeping them spaced well apart. I hope this helps, best of luck.

Name: Julie Bedington

Question: I have 2 Gardenia ‘Kleim’s Hardy’ which not flowered yet and this is my 3rd year. They’ve been kept in a frost-free greenhouse over winter and back outside for summer in May. Fed weekly from July. Part sun, part shade in pots, what can I do to get them to flower, they don't like too much sun?

Answer: Hi Julie, it could be that the fertiliser you are using has a high nitrogen content which encourages the plant to focus on leaf growth rather than producing flower buds. Alternatively, drought conditions can cause a check in plant growth and prevent flower buds forming. High night temperatures and a dry atmosphere are also known to prevent flowering. Gardenias do need fairly bright conditions - they originate from open woodlands and savannah. It’s surprising how much fences, walls and taller plants can reduce the surrounding light levels. You could try making sure your Gardenias are in a prominent position to get the maximum amount of light possible. They will happily grow in sun, just requiring some protection from the hottest part of the day. I hope this gives you some ideas Julie, best of luck.