Thompson & Morgan
Facebook Q&A Session 15th June 2012

Thompson & Morgan Facebook Q&A Session 15th June 2012 - Your horticultural questions answered.


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Name: Be Jal

Question: Can lupin plants be divided? if so when is the best time to do so?

Answer: Hi Be Jal. Lupins have a deep tap root which means that they are rather difficult to divide - but it is sometimes possible depending on the size of the clump to be divided. If you can ensure that each portion will have its own roots then it is worth a go. They should be divided in early spring or autumn for the best results so unfortunately you have missed your chance for now, until October time.

Generally however, Lupins are best propagated by basal cuttings which can be taken from March to April and will usually root fairly quickly in a sharp draining compost mix. Choose some young shoots and slice them off with a sharp knife at just below ground level where they join the main rootstock. Stick several cuttings into the compost around the edge of a 1 litre pot immediately after cutting them. Stand the pot in a saucer of water to keep the compost moist for a few weeks while they are rooting in. Hope that helps Be Jal. Best of luck with them.


Name: Steve Linden Wyatt

Question: I have side shoots on my tall rose (non-climbing) should I cut them off?

Answer: Hello Steve. Are the shoots growing from below the graft point - you will spot this as a bulge close to the base of the plant where the main stem is attached to the rootstock. If they are shooting from below this point then you should cut them off as these stems belong to the rootstock and not the variety that you are actually trying to grow. You should also remove any suckers that grow from soil level for the same reason.


Name: Steve Linden Wyatt

Question: One more regarding roses if I may. I have black spots on one of my David Austin’s. What can I do about it?

Answer: Black Spot is one of the most prevalent fungal diseases affecting roses. It infects the foliage causing irregular purple-black patches on the upper surface of the leaves. The foliage ultimately turns yellow and often drops from the plant. In severe cases, the plant may become completely defoliated and this will significantly diminish the vigour and health of the rose plant. The spores are spread through water splashes so black spot is always a particular problem during warm wet weather and can easily be blown in on the wind during rainfall. Overwintering on fallen foliage and also in infected areas on the stems, the spores will almost certainly re-infect plant the following spring if left unchecked.

There are several approaches that you can take but I’m afraid that you will need to use chemicals if you want to really keep on top of black spot. Most purpose made rose fungicides will be formulated to deal with black spot e.g. Bayer Garden Multirose or Scotts Roseclear. You can also try Westland Plant Rescue Fungus Control or Bayer Garden Systhane Fungus Fighter. It’s best to start spraying as a preventative measure in spring to stop infecting occurring in the first place. You will need to respray several times throughout the growing season. I would also suggest that you alternate the fungicide that you use as black spot can quickly develop a resistance to one brand.

Also, collect up any fallen foliage surrounding the plants in autumn and burn it to prevent spores overwintering among your roses. Try to keep an eye out for stem lesions too - these can be pruned out in early spring before the leaves emerge. I hope this helps, Steve.


Name: Sara Le Page

Question: My strawberries have long white worms in them..HORRID, How can I stop them before they ruin the whole crop.

Answer: Hello Sara. I am mystified by this. The only common strawberry pest that I know of that fits this description is the larvae of the Strawberry Tortix Moth - but these are more like caterpillars and they tend to feed on the foliage rather than inside the fruits. Are there any other symptoms of damage that might help to narrow the culprit down? I’m sorry that I can’t help you - but if you spot any more of them then I would be happy to take a look at a photo.


Name: Alan Bradley

Question: I have a christmas cactus which refuses to flower, it is in a bright position and I've had it for years, what am I doing wrong.

Answer: Hello Alan. This sort of problem is usually something to do with the plants growing environment so it should be fairly easy to correct. Schlumbergeras do require a bright position but not direct, hot sun as this may scorch them and put them under water stress if the compost dries out very quickly. It may be worth reviewing your plants current location and relocating if you think it’s a bit too bright - a west facing window is often ideal. Try to avoid positions next to radiators and draughts as dry air conditions can cause flower buds to drop.

Your Christmas cactus will also need some nutrients, particularly if it has not been re-potted for some time. If the roots look very congested then re-pot it into a slightly bigger pot. Feed your Christmas cactus every 4 weeks while in active growth with a weak solution of high potash feed to encourage flowers to form. I have found in the past that my own Christmas Cactus likes to be watered little and often. I try to keep the compost consistently moist and this seems to have improved flowering significantly. Take care not to overwater by letting them stand in reservoirs of water. Hopefully this Christmas you can look forward to seeing it flower for the first time.


Name: Lou Buff

Question: The free seeds that you sent-Zinnia EXP10 that you sent are looking very healthy about 3inches tall now-any chance they will flower this year?

Answer: Hello Lou. It’s sounds as though they are doing well. Zinnia will normally start to flower around July time but a lot of plants have been delayed slightly by the cold start to the summer. But ‘yes’ you should certainly see some flowers in the next couple of months.


Name: Sasha Gurrey

Question: My rhododendrons just don't seem to be growing. What can I do? Xx

Answer: Hi Sasha. If they were planted recently then this is perfectly normal. Like many plants Rhododendrons need to put their roots down and establish themselves below ground before they put on much leaf and stem growth. I wouldn’t expect to see much growth for the first two years. Give them time to get going. Also, some varieties are very slow growing so it’s worth checking which variety you are growing and what its growth habit is. If they are mature plants that have stopped growing then you probably need to give them a feed. Try an ericaceous feed to give them a boost.


Name: Helen Landon

Question: We have just started work installing a new playground in our village, it will be fenced but we want to line the walkway up to it with small trees, so it is marked but doesn't create a bottle-neck, any suggestions for suitable trees that are interesting but won't get too big, no prickly/poisonous berries etc?

Answer: Hello Helen. One of my favourite small trees is Sorbus (Mountain Ash). This makes an attractive small tree, casting light shade, and has plenty of interest throughout the year, with flowers, berries and good autumn colour. Better still, it will grow almost anywhere - infact you will often see them used by councils as street trees for public spaces! The raw berries can however, cause mild stomach upsets if ingested - but they are not poisonous. Sorbus vilmorinii is a particularly nice variety. You might also consider crab apples or flowering cherries, but these will have a similar problem with fruits that can cause as upset stomach - also I should warn you that crab apples can be quite messy when they drop their fruits, so these are not great for paved areas!

How about Amelanchier ‘Ballerina’? This is another good small tree for a long season of interest with pretty spring flower and lovely coloured foliage. Although it does produce berries, I am not aware of these being harmful if eaten - in fact they are perfectly edible when cooked, having a sweet, juicy flavour.

Acer psuedoplatanus ‘Brilliantissimum’ is a good choice for autumn colour. This is a fairly slow growing tree but it doesn’t produce any fruits that would tempt children. I hope this gives you a few ideas as a starting point. The arboricultural officer at your local council should also be able to give you some recommendations that they consider to be suitable plantings for this type of public space in your area, so it’s well worth giving them a call. Best of luck, Helen.


Name: Julie Atkinson

Question: Hi Sue, I bought some ground cover lily Dazzlers last autumn and planted them when they arrived. With the mild winter they came up extremely early and then got hit by frosts. I cut them down to the ground as they were all frost damaged but they've not come up again :( Are they likely to come back next year?

Answer: Oh dear. That’s a shame - a lot of people had the same problem this year. Don’t give up on them yet. Plants are surprisingly resilient and your lily might still produce some late growth this year if you are lucky, though it is unlikely to flower this year. However this growth would help to feed the bulb to ensure sufficient reserves for next year’s growth. If they don’t produce any growth this year then I can’t guarantee that they will come back next year - but it’s definitely worth waiting to find out. Fingers crossed, Julie.


Name: Jackie Rawlings

Question: What is causing my sweet pea leaves to go completely white. & brittle & then the whole plant goes white & dies. Tall & dwarf varieties are affected but it doesn’t affect my other plants. Please help. Thanks.

Answer: Hi Jackie. It’s really tricky to say without seeing the plants but it sounds rather like leaf scorch - 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.

The other thing to check for is a severe attack of powdery mildew. This is a fungal infection that causes a powdery white mould to form on the leaves and stems. It can be controlled with a suitable fungicide. However, I’m not convinced that this is the problem from the symptoms that you have described. If you have a picture then I may be able to make a better diagnosis.


Name: Lucy Garden

Question: Hi, Sue, I bought a pixirosso apple tree last year. This year it has a lot of mildew on its shoots. I read somewhere that I should prune off the mildewed shoots but will this mean I get no flowers or fruit next year? And is there anything I can do to protect it in future? I have a lot of other fruit trees which may transmit all sorts of bugs and viruses to the new tree, and it's not feasible to spray or prune them all I'm afraid.

Answer: Hi Lucy. Powdery Mildew on apple trees is relatively common, and usually associated with humid weather and dryness at the roots. For this reason it is important to keep young trees well watered during their first few years after planting.

Given that your tree is quite young, it should still be small enough for you to be able to spray with a systemic fungicide such as Bayer Garden Systhane. (Make sure that you use a spray that has been approved for use on apples.) I would try this first before you get serious with the pruning secateurs.

However, if the shoots are really severely damaged, then you may need to prune out the worst of the damage. Try to prune just the badly affected parts and avoid removing all of this year’s growth as this will reduce your crop next year.

It’s a good idea to collect up and burn any fallen leaves or plant debris to destroy any resting spores. Do this throughout the growing season and again in the autumn to prevent infection next spring. Best of luck Lucy. Let us know how you get on.


Name: Christina Goozee

Question: We have an Ash tree growing from under our garage which we cut down every year. Is there anything we can put on the cut surface to stop the tree growing? Please

Answer: Hi Christina. Use a systemic glyphosate based herbicide such as Roundup Tree Stump & Rootkiller. You can apply this with a brush and it will begin to destroy the plant from the inside. Target the outer ring of the stump, just beneath the bark as this is where the live wood will take up the herbicide. You may need to apply it several times but eventually it should do the trick. Persistence and regular application is the key here!


Name: Christina Goozee

Question: Looks too pretty to be useful so what has caused this on my Peach Peregrine even though it got a good dousing in Nov & Feb to stop the dreaded fungus.

Answer: Oh dear - it’s the dreaded Peach Leaf Curl! You did the right thing by spraying in the autumn and February. You will need to do the same this year but I would suggest that you might need to follow up your February with a second application about 2 weeks later. If your peach is wall trained then you can erect and open ended screen to cover the tree from late winter to May to keep the rain off, thereby preventing the spores from germinating. I know this sounds a bit extreme but this technique has been proven to be very successful.

For this year, I’m afraid that all you can do is pick off infected leaves the moment that you see them. Destroy them by burning them or removing them from your garden entirely - do not add them to the compost heap. Better luck next year Christina.