Thompson & Morgan
Facebook Q&A Session 7th September

Thompson & Morgan Facebook Q&A Session 7th September 2012 - Your horticultural questions answered.


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





Name: Kath Kear

Question: My lemon tree is doing well, plenty of flowers but when the lemons go yellow they are brown inside. I am watering with cooled boiled water and feeding with a specific lemon tree fertilizer. The tree is planted in a big tub and is brought into the conservatory for winter. Any help would be appreciated as they look lovely but are no good for my gin & tonic.

Answer: That’s a real shame Kath - how disappointing! Lemon trees can be quite fussy and many people struggle to get them to flower so you are doing well if they are producing fruit too. When fruits are brown inside this is often an indication of a Boron deficiency. Boron is an essential trace element which is particularly important in fruit and foliage development. However, sometimes the amount of boron available to a plant can become limited if the soil is too acidic.

If you can get hold of some borax (it is generally sold unbranded as a natural household cleaning product) then try dissolving some in water and apply it to the soil. Use a ratio of 1 tablespoon per 9 litres of water. Only apply this once a year though as too much boron will can cause further problems!


Name: Pauline Atherall

Question: Can I take cuttings of Dianthus Green Trick?

Answer: Yes, this is possible but you need to take your cuttings from non-flowering shoots in the middle of summer. It’s getting a bit late now. Use the slender shoots that appear close to the base of the plant and cut them to about two inches long. They will need to be rooted into free draining compost in warm, humid conditions.

A good tip that I have read is to root Dianthus barbatus cuttings in the border soil of a greenhouse where cucumbers are being grown, as they benefit from the same moist humid conditions and the large leaves offer the cuttings the shading that they need. Technically, ‘Green Trick’ is a short lived perennial, although it is generally grown as an annual, so it may be possible to overwinter it if you have a greenhouse. I can’t give you any guarantees that it would survive but it’s worth a try, if only to produce fresh material for cuttings next year. However, I doubt that it is the hardiest of its species however, so I would be inclined to keep it in frost free conditions. Hope that helps Pauline.


Name: Mike Fawson

Question: For next year I'm looking for tomatoes to grow outdoors in a very costal salty air environment (Sark in the Channel Islands) - any recommendations for Tomatoes that thrive in this type of environment?

Answer: Hello Mike. These conditions create a few challenges due to the salty air and wind exposure which can desiccate the foliage, but there is no reason why you shouldn’t be able to grow a decent crop with a little extra care and attention. If you can install windbreaks to shelter your tomato plants from the elements then you will have a much better chance. Make sure that you keep them well watered too as coastal winds will quickly dry the soil. Be prepared to water twice a day if necessary.

Cherry tomatoes are likely to be your best bet to start with as they are quite prolific croppers. Go for reliable varieties such as Tomato ‘Sungold’ or Tomato ‘Gardener’s Delight’. If windy conditions are a particular problem then you could also try the smaller bush varieties such as Tomato ‘Balcony Red’ in containers. These bush types have a compact growth habit which may help to lessen any wind damage. Best of luck with them, Mike.


Name: Sarah Hacker

Question: Can you 'refresh' compost so it can be reused? I grow a lot in pots so have lots to do something with. Thanks.

Answer: Hi Sarah. You can usually reuse compost for quick growing secondary crops such as salad leaves or radishes, or you might get away with planting some winter bedding in them this year. I wouldn’t recommend using it for anything that is likely to be growing over a long period though. The problem with most multipurpose composts is that they become depleted of nutrients and after a while they tend to lose their structure as the organic matter slowly breaks down. So if you intend to reuse the compost you will certainly need to incorporate some additional fertiliser; either slow-release fertiliser or a liquid feed applied throughout the growing season. I certainly wouldn’t bother reusing it more than once.

The best way to reuse compost is as a mulch around the garden. Spread it across borders and let the worms draw it into the soil. It makes a useful soil improver. You can also use some for top dressing permanent container plants such as shrubs and climbers to make them look a bit smarter and keep the pots topped up. Take care not to mound compost up around the stems of shrubs. If they are sitting very low then lift the whole rootball out of the container and pop a bit more compost in the bottom before replacing them. This should raise them up sufficiently. Hope that gives you some ideas Sarah.


Name: Keren Moulton

Question: Do Heuchera's need cutting back or should they be left alone?

Answer: Hello Keren. It’s a good idea to give them a tidy up in autumn to remove any old, damaged or diseased foliage. Heucheras are semi-evergreen if they are in a sheltered location so it’s worth leaving any leaves that look nice and healthy to give you a little colour over winter. These leaves can then be removed in the spring to make way for a nice new flush of colourful foliage.


Name: Anna Mason

Question: I have a heuchera question. Mine are standing proud and I want to replant deeper. I know it should be done in spring but can I do it now. They are between 3 and 5 years old.

Answer: Hi Anna. Heucheras naturally push upwards to reveal a woody stem above ground. You can mulch them annually to cover this but eventually they will need replanting. Late summer and early autumn is an ideal time to do this, giving the plants plenty of time to ‘root in’ before they start producing new growth in spring. They tend to be quite short lived perennials so they benefit from being lifted and divided from time to time to help rejuvenate them.


Name: Stephen Muddell

Question: Is there any organic way to remove flea beetles? Last year I grew some lovely Pak Choi but this year every sowing has been decimated, also my radishes which I understand are another favourite for flea beetles!

Answer: Hello Stephen. Flea Beetles really can make a mess of a crop. It’s the adults that do the damage. You can reduce the likelihood of damage next year by clearing away old leaf litter where the adults overwinter before emerging in spring to feed on your seedlings. The simplest and easiest way to stop them is to cover your seedlings with horticultural fleece or cloches to act as a barrier to the adult beetles. This method is often equally effective as chemical controls. Your crops are at their most vulnerable as seedlings so try to ensure that they put on rapid growth by sowing into warm soil and watering adequately following germination. Best of luck next year, Stephen.


Name: Caroline Cook

Question: After a great first 6 months having an allotment I'm wondering if Sue can advise me about what I should be planting now for over the winter. I'm in Fife, Scotland.

Answer: It’s good to hear that you have had a successful summer on your allotment, as many gardeners have struggled this year with the adverse weather conditions. Brassicas are the ideal choice for overwintering but you would normally have planted these into the ground back in early summer. Maybe something to consider for next year? However, there are other crops that you can grow outdoors now such as onions and garlic or autumn sowings of broad beans. Take a look at this article on my ‘Top 10 vegetables to grow over winter’ for some more ideas.

You might also like to put part of your allotment over to a crop of green manure which can be sown now and dug into the ground in spring to help condition the soil. You can do the same again each year on different parts of the allotment. Best of luck, Caroline. I hope that you have as much success over winter as you have over the last 6 months.