Thompson & Morgan Facebook Q&A Session 9th December - Your horticultural questions answered.

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Name: Claire Leivers

Question: Is it too late to prune my sedums? They are still in flower but the foliage has yellowed.

Answer: No it’s not too late to prune sedums. You can cut them back to about an inch above ground level. Some people prefer to leave the stems intact until spring to protect the crown from cold winter weather - this might be worth considering if you live in a particularly cold area.

Name: Patricia Morgan

Question: Why are my pansies in hanging baskets covered in mildew seems to be bad on side plants.

Answer: Hi Patricia. I am wondering if your hanging baskets have been grown in a greenhouse or are hanging in a fairly protected position. Powdery mildew thrives in poorly ventilated, damp conditions, particularly on plants which are watered from above so that the foliage becomes wet and therefore more susceptible to infection. Quite often it will occur when plants become dry at the roots. We have had a particularly mild autumn this year which will also have exacerbated the problem.

Try to keep the plants well ventilated. You may need to move them to a position with more airflow – if they are still in the greenhouse then I would definitely harden them of and move them outside. You should also treat them with a fungicide which you will be able to get from your local garden centre (it will say on the bottle whether it is suitable for powdery mildew on ornamental plants). It’s a difficult balance at this time of the year to ensure that plants are kept moist but not overwatered. You can help to reduce the risk of infection by watering in the morning, so that any water splashes on the plant will have plenty of time to dry out throughout the day. I hope this helps you, Patricia.

Name: Alan Porter

Question: Moved a magnolia from allotment into very large and deep plastic pot! Do I need to feed? Or cover with fleece? What do I do to protect and save it? Thanks for Any help Alan

Answer: Hello Alan. You have chosen the right time of the year to move your Magnolia, although be prepared to miss out on some of the flowers next year as moving it may check its growth. If this is to be a permanent arrangement then make sure that there are adequate drainage holes in the container. If you have just used multipurpose compost then it worth repotting into better quality compost such as John Innes No. 3. before it gets too settled.

I would avoid feeding it for now it until it has had a chance to root into its new container. You also need to take care not to overwater while it is in this dormant stage. Magnolias are generally perfectly hardy and shouldn’t need to be covered with fleece. The main risk to your plant is if the soil freezes for a long period, which often happens in containers. You can protect the roots of your plant by positioning it against a warm wall for the winter months. During really cold periods you can bubble wrap the container for some extra protection if necessary. Hopefully it will settle in quickly. Best of luck Alan.

Name: Kay Rogers

Question: I have a begonia in a hanging basket, which has flowered its socks off until last week. Can I leave it in the basket or should I remove it and where should I keep it over the winter.

Answer: Your begonias will definitely need protection, but it helps to know what type you are growing. Some begonias produce tubers below ground while others do not. If you received your begonias as tubers then you will know that these are tuberous types.

If they are tuberous then reduce watering as the foliage starts to die back and gradually allow the compost to dry out. Alternatively lift the plant from its container, clean the tubers and lay them somewhere dry and frost-free to allow the foliage to die completely. The dead foliage can then be removed and the tubers stored in containers of dry sand or peat (or even in paper bags) somewhere cool and frost-free. Keep them at a temperature of 5-10C. If your Begonia is not a tuberous variety then simply bring it indoors to a bright, cool and frost-free position (a slightly heated greenhouse or conservatory is ideal). Water sparingly as Begonias are susceptible to stem and rhizome rot. You can move it back outside in late spring after the risk of frost has passed. Hope this helps Kay.

Name: Andy Preece

Question: What do you think of biodynamics? Do you think it's worth a go or just a load of old rubbish?

Answer: Biodynamics… Hmm, an interesting question (and exactly the sort of question I enjoy because it makes me think about a principle that I might never have had the opportunity to consider previously!)

I have to say that my knowledge of biodynamics is fairly limited, but my understanding is that one of the main principles is that of working with nature, rather than trying to dominate it – a principle which sits very comfortably alongside organic gardening. I am all in favour of this. However, it is the second key principle that I am undecided about – the idea of setting out and working with the invisible energies and forces that exist around us. Certainly the idea of carrying out particular activities to a lunar calendar sounds a little wacky at first. But when you scratch the surface of biodynamics there lays a carefully considered theorem beneath the stereotype of eccentric gardeners tending their plots by moonlight!

Moreover, I can’t shake that nagging feeling that maybe I am missing something. People who practice biodynamics often state that there is just a different ‘feel’ to their garden; something indescribable – but definitely different. As someone who has never practiced biodynamics, who am I to say that it is rubbish? So Andy, in answer to your question – I am sceptical, but not entirely closed to the idea. I’d be interested to know yours and anyone else’s views on the matter, particularly if they have tried biodynamic gardening.

Name: Kevin Joseph

Question: I have a what i think is 2 years old cherry blossom tree. However i want the tree to branch out more because it seems the branches are just going up and up in a long line. Shall i prune the tops out and when is it a good time to do this as i dont want to lose next years spring flowers. Thanks

Answer: Hi Kevin. You can thicken the crown of your tree by pruning the tips of a few carefully selected branches as shown in the picture. This will break its apical dominance (the process by which the main stems grow more strongly than the side stems), and will help to encourage buds below the pruning wound to break dormancy.

Don’t get carried away though – remember that you are trying to enhance the shape of your tree, and every cut that you make will cause changes that will remain with the tree permanently. It will take a few years before you can see the full effects but it will make a better shaped tree in the long term. Remember though – just a couple of snips Kevin!!!

Name: John Fowell

Question: I keep reading this on plant care, "Fertilizer: From spring through summer, feed monthly with a balanced fertilizer diluted by half." What does it mean by 'diluted by half' please? Does it mean that I follow the instructions on the feed bottle but half it? Cheers. And also, can you identify this plant please as I've searched and searched and cannot identify it. I'm propagating it from a friend's house plant and it's starting to root in the glass of water I put it in and I want to know what it is so I can research how to plant it and care for it. Cheers again! :o)

Answer: Hi John. When plant care instructions tell you to apply fertiliser ‘diluted by half’, what they are actually saying is that it should be half the recommended strength. That is, you should make the fertiliser up using the recommended amount of water but only half the recommended amount of fertiliser concentrate – compare it to making a very weak glass of cordial!

I agree with Be Jal – your plant is a palmate leaved begonia, but there are so many different varieties available that I am unable to give you a specific cultivar name. It will enjoy a warm position in bright, indirect light. Begonias are easy to propagate from cuttings as you have already discovered. Once it has developed a good set of roots you can pot it up into a free draining compost. Water sparingly when necessary to keep the compost moist but not wet. Good luck with it John.