Thompson & Morgan Facebook Q&A Session 13th July 2012 - Your horticultural questions answered.

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Name: Bev Parker

Question: I brought a hibiscus plant 3 years ago, it is planted in the garden, which is south facing and has not flowered. Otherwise looks healthy, I have not pruned it. I have others that have been planted in pots outside and they have all flowered. Any suggestions.

Answer: Hello Bev. It sounds as though your Hibiscus is enjoying its freedom and putting all of its energy into making roots and vegetative growth instead of flowers. Being planted in the soil gives this plant access to more nutrients and soil moisture than being planted in a pot. Many plants flower in response to being slightly stressed – after all, flowering and producing seed is a method of species survival. This is why your pot grown plants have bloomed earlier. By restricting their root growth and limiting access to water and nutrients, they have responded by producing flowers. You will, of course, need to replace the nutrients by feeding and watering regularly.

Don’t worry - your Hibiscus grown in the ground will catch up in time and will probably be much healthier in the long term. If you are feeding it then I would suggest that you use a high potash feed to encourage flower bud formation. Avoid using nitrogen rich fertilizer such as tomato food as this will encourage lots more foliage but no flowers. I hope that helps Bev.

Name: Tracey Williams

Question: I’ve grown four cayenne pepper plants from seed. They have grown really well lots of flowers but all of a sudden the flowers have started dropping off. I assumed from the flowers the peppers would grow. They are in a warm conservatory. What have I done wrong? Is it over/under water? Not enough sun/air? I'm devastated as I have been nurturing them.

Answer: Hi Tracey. You may not have done anything wrong. The fruits do form from the flowers but the petals will always naturally drop as the flower fades. Take a closer look at where the flowers used to be and you may see some tiny peppers beginning to swell.

However, if you can’t see any evidence of fruit forming then there may be a simple explanation. Pepper flowers are usually pollinated by insects but as your plants are in the conservatory it is likely that there are few insects in your home to undertake this task. There are two solutions to this problem. The first would be to stand your chilli peppers outdoors when they are in flower so that the insects have access to them. The other alternative is to do the job yourself. Once a day while the plant is in flower you can take a fine paintbrush (or a cotton bud) and gradually work your way from bloom to bloom tickling the centre of each flower with the brush. This will transfer pollen between the flowers and allow pollination to occur. Unfortunately, without pollination you won’t get any chillies.

With regard to watering, it’s best to keep your plants slightly on the drier side. Over watering can cause also cause flowers to drop so make sure that the compost is kept moist but not wet. For more information take a look at our How to grow chillies article.

Name: Anna Boluda

Question: I have a question for your expert. My plants -tomatoes, cucumbers and beans in big pots, mainly - are suffering a terrible plague of red spider mite for the second year in a row. I have tried ecological options - neem oil - as advised from my local store, but it doesn't seem to work. What can I do? I'm pretty desperate. I'm ready to use chemicals if that's the only way to save some of the plants :( Greetings from Barcelona

Answer: Hello Anna. Spider mite is a particularly tricky pest to control and can cause devastating damage in severe cases. Your local store was quite right to suggest neem oil as you are growing edible crops. There are chemicals available that will help to control spider mite but these are aimed at ornamental plants and should not be used on edible crops.

There are several things that you can do to reduce the spider mite population. Firstly biological controls such as the predatory mite Phytoseiulus persimilis are the most effective control against spider mite. This particular predator reproduces at twice the rate of spider mite. It is highly active under hot dry conditions, where just one mite of P. persimilis can consume 20 eggs or 5 adults per day! However, it requires a minimum temperature of over 16C (although daytime temperatures of 21 ºC are preferable) and there needs to be sufficient numbers of spider mite present for the predatory mites to feed on.

There are also a number of cultural practices that you can also use to help prevent and reduce outbreaks. Spider mite thrives in warm dry conditions, so damp down greenhouse floors and paths to increase the humidity. Regular inspection of the undersides of leaves will also help to detect the problem before it spreads. At the early stages of attack you can pick off and burn any infested leaves when you find them. Finally, at the end of the growing season, make sure that you take time to really clean up properly as spider mites like to spend the winter hidden in dry crevices and plant debris until the weather warms up again in spring. I hope this helps you to reduce the problem, Anna.

Name: Daniel Stewart Marshall

Question: Hi, I have a question for Sue. I have just harvested my T&M; first early onions. Unfortunately, due to the weather they all bolted. Everyone says they don't store too well after bolting, but I can't find any information on how long they actually keep for. Should I start giving away/ freezing or are they all right for a while?

Answer: Hi Daniel. This year has been terrible for onions – so you are certainly not alone. At best you are looking at about two or three weeks. Try to dry them out a bit by laying them out on the greenhouse bench or, if the sun ever shines again, you can spread them out on dry ground for a day or two. You really need to start using them up as soon as possible though. If you have a lot of onions then I would suggest keeping enough for the next three weeks and freezing/ giving away the rest. That way you shouldn’t have to compost too many.

Name: Adam Jacobs

Question: Well, I'm having a pretty catastrophic year in the garden, and suffering from the slugpocalypse that I gather is affecting quite a few others as well. One of my biggest disappointments is that my first sowing of borlotti beans has been destroyed completely. Is it too late to try again with another sowing? And if it's not, I'm thinking of starting them off in the greenhouse and then planting them out after they've got big enough to at least have a chance of fighting off a concerted slug attack. Does that sound like a sensible plan?

Answer: Hi Adam. Yes you still have time to do another sowing if you are quick. I would certainly recommend that you start them off in the greenhouse – sow them into large module trays and plant them out once they are well established. However you will still need to keep an eye out for slugs in the greenhouse, and I’m afraid that you will probably need to resort to slug pellets when you first plant them out. Best of luck.

Name: Ilya Burkin

Question: Hi. Could you help me and explain what is wrong with my Honeysuckle Americana and how I can save my plant? It is getting brown-yellow-powder in the lower part of the plant. Thank you very much in advance.

Answer: Hi Ilya. It looks as though your honeysuckle is suffering from the fungal infection sooty mould. This is very common on honeysuckle and tends to be a secondary infection on plants that have been attacked by aphids. Unfortunately honeysuckle is particularly prone to aphid attack as they love to feed on the sap of the young shoots. Aphids excrete a sticky substance called honeydew which in turn, attracts sooty mould which colonises these sticky areas.

Firstly you need to check your plant for signs of aphids. They are not always obvious so take a really close look, especially at the growing tips of the shoots where the stems are softest. These can be treated by squashing between your finger and thumb or spraying them regularly with a diluted solution of soapy water. If the infestation is very heavy then you may need to resort to chemicals.

Once this problem is under control you will find that the sooty mould will decrease naturally. If you have the patience then you can wipe the leaves clean with more soapy water but patches of sooty mould will often flake off over the course of the summer. I hope that helps.

Name: Gaz RocknRolla

Question: Got problems showing up on my fruit trees "leaves". Walnut: part of the leaves are brown/black with white dots. Hazelnut; brown on the cornering of most leaves. And apples: the leaves are curling. Guessing it maybe fungal or something. If so, what is it and how do I get rid of it please?

Answer: Hi Gaz. It’s really hard to answer questions like this without at least seeing a picture of each of the problems. If this is a fungal problem then you can try spraying with a suitable fungicide but you will need to check that it is ok to use on fruit/ nut trees as some are only suitable for use on ornamental plants. Also check the persistence of the fungicide if you want to harvest the nuts as you don’t want to contaminate your entire crop.

Curling apple leaves are often caused by a pest such as aphids. Take a closer look at your tree to see if you can spot the problem. Uncurling the leaves will sometimes reveal a pest sheltering inside. Aphids can also be controlled by spraying with a suitable insecticide. As with your nut trees, you need to bear in mind that your fruits are now beginning to develop and you don’t want these contaminated if you intend to eat them.

Sorry to be a little vague, Gaz. If you can provide some pictures and a fuller description of the damage then I can try to give you a more specific answer.

Name: Yvette Britton

Question: My greenhouse cucumbers are not doing well at all! They are 'picolino'. Plants are now 4-5' high but leaves are turning yellow then brown and crispy. I have reduced watering slightly as research seemed to indicate they may be too wet (watering is via irrigation hose set for 30 mins a day). Some fruit are appearing but not as much as I should be getting according to your website! I'd be grateful for any advice.

Answer: Hello Yvette. There are lots of other reasons why the lower leaves can turn yellow, but more often than not it is simply a nutrient deficiency. Try giving them a liquid feed - tomato fertiliser will usually do the job. Overwatering and underwatering can also turn the leaves yellow – water regularly to keep the compost moist but not soaking wet. Also make sure that your cucumbers are shaded from the sun as the leaves can be easily scorched. Shade paint is the easiest solution for this problem. It worth damping down the greenhouse paths on hot day too, as this helps to increase the humidity in your greenhouse. For more information take a look at our How to grow cucumbers article.

Name: Jackie Orton

Question: Not sure what it is, but it was from a collection I bought from you earlier in the year. Can you tell me what it is called and whether I can easily over winter it?

Answer: Hello Jackie. This looks like one of the giant fuchsias, maybe ‘Royal Mosaic’. It’s not a hardy variety so you will need to overwinter it in a frost free greenhouse or conservatory. Bring it in before the first frost and reduce watering so that it is kept moist but not wet during the winter months. You will be able to return it outside in late spring or early summer next year.

Name: Tracy Trotter

Question: I’m getting a white mould/fungus in my green house for the second year running... I did set off a sulphur candle before I started this season... can you give me some help as it kills everything.

Answer: I’m not quite sure what you are referring to without a picture, but if it is predominantly on your plant leaves then this is probably powdery or downy mildew. These fungal infections show as a white powdery mould on the upper (powdery mildew) or lower (downy mildew) leaf surfaces. Improving air circulation will certainly help. Make sure that you ventilate your greenhouse during the daytime particularly after watering so that it dries out properly. Also try to avoid plants being crowded together as this reduces air circulation and allows spores to spread.

You can spray your plants with a suitable fungicide. These are available at all good garden centres and will say on the bottle whether they are suitable for powdery mildew and when to apply. As with any chemical, do check it is suitable for use on edible crops before spraying your fruit and vegetables.

In order to avoid the same problem next year it is essential that you have a really good clean up in autumn to prevent the spores overwintering. Clear all debris from the nooks and crannies in your greenhouse and wash the whole place down with a horticultural disinfectant. Clean all of your pots and equipment too. Hopefully this sounds familiar to you, but if I have misunderstood your question then please get in touch. A photo is always useful for this kind of diagnosis.

Name: Anna Rosewell

Question: I bought some Dianthus 'Ipswich mixed' last spring. I have grown them on in pots in a gritty compost mix with slow release food included and they look really big, bushy and healthy, but no sign of any flowers. I am based in Oxfordshire. Is this just because of the total lack of sunshine we have had this year?

Answer: Hello Anna. It sounds as though they are getting well established. As you rightly pointed out, it’s been a very cold growing season so most plants are well behind the stage that you would normally expect them to be at this time of the year. I’m afraid this means you will need to stay patient for the time being. Hopefully they will provide you with a few flowers before the end of the summer, but if not then they should certainly make up for it next year. Let’s keep our fingers crossed for some sunshine soon.

Name: Ilya Burkin

Question: Hello, how can I get rid of earwigs in the garden? they damage flowers and sensitive leaves. Thank you.

Answer: Earwigs start to feed once the weather becomes warm in spring. They are active at night so you’re unlikely to spot them doing the damage during the day. To diagnose if this is earwig damage, place a pot loosely stuffed with straw or shredded paper upside down at the base of the tree. Earwigs will hide in the pot during the day so you should find them there in the morning. If you do find earwigs you can either keep emptying the pot each day and destroy them, or spray them with an insecticide at dusk when they are active, or spread ant powder around the affected area. Although earwigs can be a pain they are actually beneficial to the garden too! They eat small insects and eggs so are a good natural pest control.