Thompson & Morgan Facebook Q&A Session 21st September 2012 - Your horticultural questions answered.

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Name: Rosalinda Mataro Dumanig

Question: What fertilizer should I use to bloom my hydrangeas?

Answer: Hi Rosalinda. If your plant simply needs feeding then I would suggest that you use an ericaceous fertiliser. This will help to keep the plant in top condition, promoting plenty of growth and flower production. Fertilisers are best applied in spring and summer while the plant is in active growth. At this time of the year you might be better to provide a good mulch of well rotted manure around the base of the plant instead, and then start feeding the plant from next spring.

However, if you are trying to turn your pink hydrangea flowers to blue then you will need to grow your hydrangea in an acid soil. (White flowered Hydrangeas will stay white regardless of soil type). If you don’t have acid soil then this can be achieved by growing the plant in a large container, and planting it in a mix of ericaceous compost and John Innes No. 3. Make sure that you water it with rain water though, because tap water will turn the soil more alkaline over time which will cause your plant to turn pink again.

You can also provide your plant with Hydrangea colourant or Chempak sulphur which helps to maintain the acidity in the soil. This product is usually applied in the spring. Don’t use all of these products at the same time though - just one will be sufficient!

Name: Phil Dulake

Question: Could you tell me the pruning group of my clematis I got from you - I can’t remember! I got Clematis Ville De Lyon, Clematis Hagley Hybrid and Clematis Ernest Markham...

Answer: Hello Phil. I get lots of questions like this, but usually people can’t remember which variety they have which makes it difficult to answer! Your clematis are all from pruning group 3 which makes them really easy to deal with. Every year these plants can be completely cut back to a pair of strong buds about 20cm (8") above ground level, removing all of the previous year's growth. Ideally you should prune group 3 clematis in spring before they start into active growth. Hope that helps, Phil.

Name: Tracie Watson

Question: How do I improve my clay soil on a small budget. Been told grass clippings, is that true? If so are they fresh clippings or will that not work - and I don't really have the space to store them, please please help x

Answer: Hi Tracie. People often feel slightly disadvantaged by having a clay soil but actually clay is extremely fertile and you can grow a really good range of plants on clay.

Unfortunately grass clippings are not ideal for improving soil structure - and certainly not fresh ones, although you can use them in moderation as a mulch. They tend to rot down to a smelly mush if they are not mixed with drier compost ingredients such as scrunched up newspaper, autumn leaves etc.

The best thing to do with clay soil is to improve it by digging in lots of organic matter such as well-rotted manure, compost or recycled green waste. It needn’t cost a fortune either. Old multipurpose compost from patio containers will work nicely, plus any homemade compost from your compost heap. Autumn gives an ideal opportunity to collect fallen leaves in bin bags. Mix some of your grass cuttings in with them and make a few aeration holes in the side of each bag. Then stack them out of the way until this time next year. This will give you lots of lovely leaf mould for free that will definitely help improve your soil structure.

Also speak to your local stables or farmers. They will probably be very pleased to get rid of some manure if you are prepared to bag it up yourself - always take the well rotted stuff from the bottom of the heap! You could even place a post on one of the recycling sites such as Freecycle - there might well be horse owners in your area that could help. It’s also worth asking your local council if they sell recycled garden waste as soil conditioner. This is often cheaper than buying it in bags from garden centres. Hopefully this gives you a few ideas, Tracie. Best of luck.

Name: Elizabeth Katherine Kirby

Question: Hi, I wonder if you could tell me where I am going wrong with my peonies. They come into bud and then the bud goes black and drops off. I have had some flowers in past years but nothing at all this year although there were more buds and I was hopeful of a beautiful display. Help!

Answer: Hi Elizabeth. This is quite a common problem with peonies - my own peony does the same thing! It tends to be caused by environmental conditions, some of which can be remedied by reviewing their growing conditions and others are simply out of your control.

Take a look at your peony and check that it is growing in moist, rich fertile soil with good drainage and situated in full sun. I find that peonies are not keen on competition either - mine is situated close to a small tree and really doesn’t enjoy this location.

If all is well with its growing conditions then you will often find that the problems are related to spring weather. Late frosts and dry periods in spring are the main cause of peony buds failing. There is little that you can do about this except to ensure that they are not planted in a frost pocket and to keep them well watered. We did have a very dry spring this year so this may well have been the cause of your problems, given that your plants have flowered well in the past. Hopefully next year you will have more success.

Name: Lynn Baumbach

Question: My saffron crocus have never flowered they green up and do nothing else they are in a large pot. What do I need to do for them to flower?

Answer: Hello Lynn. You don’t mention how long they have been planted in your containers but if they have been there for a few years then it might be worth repotting this autumn into fresh, slightly gritty compost with some slow release fertiliser mixed in. Make sure that they are not too overcrowded as this can reduce flowering. Keep your containers outdoors over winter so that they get a really good chilling period and position them in full sun as soon as you see signs of growth.

It’s also worth covering the containers with chicken wire or an upturned wire hanging basket until the flowers come out. Crocuses are particularly prone to damage by birds who will attack both the flowers and the buds. There is the possibility that your bulbs may have been producing buds but that they are being stripped by birds before you even spot them. Hopefully, they will produce a better display next spring.

Name: Karen Stott

Question: My bottle brush plant is 4 years old in full sun and never flowered. How can I get it to flower?

Answer: Thats’s a shame Karen. Bottlebrush plants look fantastic in full bloom but they do need a good sunny spot and moist, fertile, but well drained soil. They can be quite slow growing, but I would have expected some flowers by now.

If you are growing your Callistemon in a container then it may well benefit from repotting into fresh compost. Use John Innes No.3 with some slow release fertiliser mixed in as this will have better structure and fertility than an ordinary multipurpose compost, so it will benefit your plant for longer.

If your plant is growing outdoors in a sheltered border then it’s worth applying a mulch of well rotted organic matter this autumn. Follow this up by starting a feeding regime in spring, using a Aa href=" https://www.thompson-morgan.com/garden-supplies/fertilisers/chempak-high-potash-feed-formula-4/kww2324TM">high potash feed