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Sue's Facebook Question and Answer Session - 3rd September 2010

Name: Jane Carter
Question: My son has a Japanese Maple bush and the leaves have tiny white speckles all over them, we can't see any sign of bugs, has anybody got any ideas as to what may have caused this please?

Answer: Hi Jane, without closer inspection of the plant it is difficult to say what the problem might be.

It is possible that your maple has a fungal infection. If so, then the best course of action is to clear up the fallen leaves this autumn and dispose of them in your normal household waste or burn them to destroy overwintering spores.

If the speckles are bumpy and appear on the underside of the leaves and stems, this could be scale insects. The insects cocoon themselves in small hard protective ‘scales’. There are chemical controls available readily in most garden centres – each product will list if it is effective against scale insects and the types of plants it can be used on. The best time to spray is from June to July as this is when new insects hatch.

If you could attach a picture then I will take a closer look.

Name: Kevin Joseph
Question: Can anyone recommend a good soil ph tester? Thanks

Answer: Hi Kevin. Testing your soil pH is a great idea. It will give you a much better understanding of the soil conditions that your plot can provide, which allows you to select species that are best suited to your garden. pH is a measure of soil acidity or alkalinity on a scale from 0-14. Neutral soils have a pH value of 7; acid soils have a lower value than this and alkaline (limey) soils have a higher reading. Most plants do well in a neutral soil measuring a pH of 6.5 – 7, although some require more acidity (ericaceous plants) and others enjoy an alkaline soil.

There are lots of soil testers out there that test by either chemical or electronic means, with greatly varying prices and equally varying levels of accuracy. If you just want to know what the pH level is then you should be able to pick up a small disposible kit from your local garden centre - these are fairly inexpensive. They will tell you if it is an acid, neutral or alkaline soil. These domestic kits rely on the use of a capsule that, when mixed with water and a small quantity of your soil, produces a colour that relates to a colour scale rather than a numerical value. I have used this type of kit myself and I would recommend buying more than one capsule though as it is a good idea to test from several positions across your plot instead of just one place.

The more expensive kits will be able to give you N:P:K measurements as well, but remember that these will change each time you add fertilisers and soil improvers to your plot so you will need to retest the area.

The more complex and expensive test kits are aimed at farmers, professionals, and garden geeks who would just want to know everything about their soil, but these are over and above the requirements (and budgets) of most gardeners.

Name: Di Shaw
Question: Sue, what do we do with the heads of sunflowers to get the seeds for next year, I have 13 heads?

Answer: Ideally you should leave the heads of the sunflowers on the plant for as long as possible – until they turn brown; although they can be cut when the back of the flower heads turn yellow. This may be a better option if you don’t want the birds to get the seeds first! Cut the heads off along with about 30cm of the stem and hang them upside down somewhere dry like a garage or shed. Wrap a paper bag around the heads or hang them over a tray to catch any seeds that fall. To prevent mould make sure there’s good air circulation.

Name: Julie Thomas
Question: Hi I have planted asparagus this year which seem to have taken well, can you advise me if I should cut the fern growth back for winter and if so when should I do this. Many thanks

Answer: Hi Julie, when the foliage turns yellow cut the stems back to about 2.5cm above the soil level and mulch the crowns with well rotted manure to protect them from frosts.

When growing asparagus, it is important to resist the temptation to harvest the spears during their first season, but instead allow the plants to develop foliage. A limited crop of spears can be harvested in the second year during April and May when they reach 15cm (6”) tall. By the third year, the crop can be fully harvested. It is recommended to stop cutting from the end of May to allow the shoots to develop into foliage. Later harvests can be made but these will risk weakening the plant.

Name: Tracey Dawson
Question: We have just built a dry stone wall around the edge of our raised bed. Can you advise me of plants that we can grow in the gaps along the wall? Thanks. Tracey

Answer: Hi Tracey, what a great idea! The sorts of plants suitable for growing in walls often originate from mountainous areas. Acantholimon glumaceum is a small evergreen perennial with pink flowers in the summer. Chiastophyllum oppositifolium is also evergreen and is trailing. It has erect flower stems in late spring and early summer bearing yellow flowers in arching sprays. One of my favourites is Erigeron karvinskianus ‘Profusion’ (Fleabane/Mexican Daisy) which will grow just about anywhere and continuously flowers all summer. You could also try Orange-Scented Thyme which is valuable to insects as well as providing a herb for cooking. Other varieties of creeping Thyme will also work well. Sedum is a classic rock/wall garden plant that thrives with very little water and spreads to form a carpet of foliage and colour. In moist, shady area you could also try some of the smaller Asplenium species. These little ferns are often seen growing in stone walls and crevices and will establish surprisingly quickly. I hope this gives you some ideas of what to plant, good luck!

Name: Sue Boniface
Question: I received Pansy Plentifall and Viola Pot Pourri mixed whilst I was away (so much for a September delivery) and my very helpful neighbour opened them and potted them all up for me – not realising they were different – how do I tell which is which?

Answer: Oh dear, Sue. If you give them a few weeks then you should be able to tell them apart. Viola Pot Pourri Mixed will have smaller foliage than Pansy Plentifall and should come into flower slightly earlier. Another giveaway will be the trailing habit of Pansy Plentifall which should start to become more prostrate as it grows. Hope this helps.

Name: Sue Boniface
Question: As part of the Chelsea celebration pack I received Geranium skyrocket – do they not get to climb in their first year – everyone is driving me mad asking what’s going to be on the obelisk which these are planted around.

Answer: By next year, your Geranium Skyrocket should have settled in nicely and it will begin to produce the long stems that you are waiting for. It is not a natural climber so you will need to guide the stems onto the obelisk and tie them in with soft twine. I am assuming that you have planted it in a container. You will need to move the container to a bright, frost free position over winter with a minimum temperature of 7ºC (45ºF) to protect it from the cold. Also, reduce watering during the winter months so that the compost is kept just moist. Hopefully you will have a fantastic display next year.

Name: Petra Rühle
Question: Help, do you know something against spider mite? Organic if possible.

Answer: Spider mite is a particularly difficult pest to eradicate as it readily develops tolerance to chemical controls and generally requires several applications of chemicals in order to eradicate all stages of the lifecycle (mites, nymphs and eggs).

Therefore 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 16ºC (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. Obviously, if you choose to use biological control then you cannot also use chemical control as this will kill the predatory mites!

There are 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. 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 out your greenhouse properly as spider mites like to spend the winter hidden in dry crevices and plant debris until the weather warms up again in spring.

Name: Kevin Joseph
Question: This is a question for Sue, who i hope can explain why my Hydrangeas blooms hasn’t gone full circle.

Answer: Hi Kevin. The reason you do not have fuller flower heads on your hydrangea is because you are growing a lacecap variety. Lacecap forms have flattened flower heads with a circle of large sterile blooms around the outside and a mass of tiny fertile flowers in the centre. The fuller flower heads appear in the hortensia (mophead) varieties such as Hydrangea Tivoli or Bavaria.

Name: Helen Miller
Question: Question for Sue...Any ideas what is wrong with this conifer? It's been fed and watered regularly. Thanks

Answer: Hi Helen, it looks as though the foliage is browning from the centre of the tree and working its way out along the branches. The dieback is also scattered throughout the tree. This is very suggestive of a soil borne fungal infection such as Phytophthora root rot to which conifers are particularly susceptible to. This type of root rot occurs most frequently in warm wet soils. Given that you have watered it regularly and it is planted in a sheltered position, I would imagine that such conditions are present. There are no chemical cures available for this problem so it is recommended that infected plants are removed and destroyed.

Prevention is generally better than cure. If you decide to replace the plant you will need to improve the soil well before replanting and avoid excessive watering and mulching with manures that hold water in the soil. If you are gardening on heavy clay then perforate the sides of the planting hole before planting your tree to ensure good drainage.

Name: Chrissianne Carpenter
Question: This is for Sue for her Q & A - please can you tell me how to prune a grafted M26 (I think) apple tree? I have two - a Grenadier and a Red Windsor. They are bare limbed with bunches on the ends - not right I think. And the fruit this year has caused the limbs to bow or even break under the weight..thank you.

Answer: Pruning apple trees normally begins immediately after planting. Remove the central stem to just above the highest side branch. For the following 3 years, prune only the tips of the remaining main branches by one third in winter. Aim for about six main branches which will form the frame of your tree, with fruiting sub branches growing off of them. From the fourth year, some sub branches can be pruned out at the union where they join the main branch, to allow new sub branches to take their place.

However, if you are dealing with overcrowded mature trees then you may need to do some renovation pruning to restore the tree to a nice open shape and improve air circulation and light penetration. But be careful not to remove more than 25% of the canopy per year. This type of pruning should also be undertaken in winter. First remove all damaged, dead, crossing and diseased branches. Then remove any crowded branches to create a nice, even framework. Once you have thinned out the unwanted branches, you can begin a regular pruning regime, removing older fruiting spurs so that younger ones can replace them. You will need to spread this renovation process over several years though so it will require a bit of patience and may also reduce your crop initially.

Name: Wayne Brewin
Question: Question for Sue's Q & A tomorrow - I tried taking cuttings for the first time from several plants I have brought this year and been surprised to find out that I have successfully managed to root them. They are from Fuchsias, Begonias and Dahlias (I realise they are not the hardest one's to propagate.) I believe I have to now keep them in my greenhouse over winter, however I only have one of those plastic greenhouses (4ft x 4ft) which will keep the frost off and I am able to keep the temperature above freezing with a small heater I have so a) will this be sufficient? and b) how wet do you keep the compost the cuttings are growing in?

Answer: Well done with your cuttings. If you don’t have a greenhouse then you might be better to keep them in a heated conservatory or on a bright windowsill indoors. Perhaps you have a kind gardening friend or neighbour who could spare some heated greenhouse space? I’m afraid that the little plastic greenhouses are generally very difficult to keep frost free given the small volume of air within them. It would be a constant battle to keep the temperature up and would not be very economical.

You should reduce watering over winter so that the cuttings are kept moist but never wet or waterlogged. Keeping them on the drier side will also help to protect their delicate roots from the cold. Of course, if they are in a heated greenhouse then they will dry out much quicker than they would on a cool, bright windowsill! Best of luck, Wayne.