Facebook Questions and Answers for the 3rd August 2012

Hello Facebook fans, thanks for your questions this week, here are Carly's replies:

Stephen Parker

I have a question...I have some standard bay trees, one has got very thin on top! The head is see through now and spoils the effect. Can I prune hard or feed or do something else to regenerate it please?

Hi Stephen, I'm wondering whether the leaves on your bay tree are showing signs of stress such as yellowing or black spots? Pests, diseases and nutrient deficiencies are all contributing factors to weak growth so it's worth resolving these problems before pruning. Try inspecting your plant and checking the underside of the leaves for scale insects which are a common problem on bay trees. They appear as yellow bumps on the leaf, like tiny limpets and cause yellowing leaves and poor growth. If you find evidence of scale insects then they can be sprayed now whilst their young are freshly hatched– sprays are available at all good garden centres and repeat applications may be needed. Along with scale insects, nutrient deficiencies and waterlogged compost/soil will also cause leaves to yellow. If your bay tree is growing in a pot it may need a change of compost; compost naturally breaks down over the years causing poor drainage and poor nutrient-retention. To do this simply remove your bay from its pot and trim a third of the roots off the bottom before placing in fresh compost. You can also replace the top inch of compost with fresh compost.

Bay trees can tolerate hard pruning but are slow to recover so it's best if you carry out a light prune now. Make your cut just above a bud and at an angle away from the bud. Apply a balanced liquid feed every week or so until the autumn to keep your bay tree healthy. If your bay trees are growing in pots they'll need feeding every year during the spring and summer, either with a liquid feed every few weeks or a slow-release fertiliser applied once in the spring. You can apply a slow release fertiliser to plants growing in the ground in the spring too. Hopefully your bay tree will respond with some lovely new growth and next summer you will be able to shape it further if needed! I hope this helps, best of luck.

Christina Goozee

How should I prune & take a cutting from my Raspberry shrub which has just finished fruiting pls? Also will you also advise the best way to prune a pot grown Magnolia please?

Hi Christina, with summer-fruiting raspberries the aim is to cut out all canes which have fruited this year and leave the new shoots to grow on, tying them in to a support as they grow. Simply cut all fruited canes right back to ground level now.

You can select your cuttings from the material you prune out, which at this time of year will be semi-ripe. Start by cutting pieces of the raspberry cane into 10-15cm lengths, making your cuts just below a leaf node (joint). Remember which way up the pieces were growing as they won't root if put in upside down! Remove the lowest leaves on the cuttings, leaving no more than four growing. Dip the bottom of the cuttings in hormone rooting powder or gel and insert them into pots of compost. It's best to use a mixture consisting of 50% compost and 50% perlite for good drainage and root aeration. Water the pots well and allow excess water to drain. Cover your pots with a clear plastic bag and place them somewhere warm and bright but away from direct sunlight. Make sure the compost stays damp for good rooting. They should root quickly at this time of year - look for lots of white roots appearing in the drainage holes of the pots before potting on into individual pots, or planting directly outside. If leaving your cuttings in pots for the winter it's best to put them in a cold frame or against a house wall to offer a little root protection.

With regards to your potted magnolia it's best to only lightly prune if needed. Heavy pruning can spoil a Magnolia's natural shape by encouraging 'water shoots' (long, vertical, upright shoots) or dieback. Between now and September is the best time of year to give your magnolia a trim. It's really a matter of personal taste as to what shape you'd like your Magnolia to take, but whenever you do make a cut, make it just above a bud at an angle away from the bud. I hope this helps Christina, we'd love to hear how you get on.

Maria Weaving-Gómez

Why are my French yellow beans not growing? They are healthy, in fact, they are even flowering but yet, they are quite small, no more than 20 cms. Any clues..?

Hi Maria, it sounds like you may be growing a dwarf variety of bean; these varieties only grow about 30-45cm tall. If you had a climbing variety of bean it would grow most of the way up its support before starting to flower. Even though they may be a dwarf variety the cool weather could also be playing a part in their very short growth. My dwarf bean plants are slightly smaller this year too although this shouldn't affect cropping and I eagerly await my first harvest! I hope this helps.