Facebook Questions and Answers for the 17th February 2012

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

Audrey Harrison

I have 2 mimosa plants in pots, 2 years old, long and thin with few leaves at top!!!! Do I cut them down in spring? and use tops as cuttings??

Hi Audrey, as your mimosas (Acacias) are so young it will be fine to prune out the top. This will encourage your mimosa to become multi-stemmed and bushier in appearance. Pruning is best done just after flowering in late spring or early summer. Unfortunately the cutting may not root very well as Acacia cuttings are best taken when 'semi-ripe' in mid-summer. This is the stage at which new spring growth starts to harden off, but before it becomes woody in the autumn.

To prune your mimosa simply make your pruning cut above a side shoot or bud. You can prune your tree to any height you desire but for a full and bushy appearance it's best to prune fairly low down on the trunk. If you have a vigorous species such as Acacia dealbata then you can cut as low down as 10cm (4") and the plant will regenerate well. Make sure you water and feed your mimosas regularly for the remainder of the summer to help them put on healthy new growth. Next year, once new growth has developed it's best to thin out the new shoots to prevent overcrowding. Select 3 or 4 of the strongest shoots and then prune out all others to the base. I hope this helps Audrey, good luck!

Laura Mounsey

Any tips on keeping coriander plants in the home? I am managing to keep basil and parsley alive but I'm doing something wrong with coriander.... any tips would be great. Thanks!

Hi again one more question.... last year all my bedding plants were eaten by slugs, seemed like such a waste of money, are there any plants they don't like or best advice on deterring them pet & child friendly? Not had this issue before, everything I planted last year was devoured by them

Hi Laura, coriander is definitely one of the more tricky annual herbs to cultivate and will try to flower at any opportunity! I too struggled to grow coriander on the kitchen windowsill last year. Unfortunately a lot of this is just the genetic makeup of the plant but they will flower and lose their basal leaves (the bit we eat) faster if exposed to too much heat or dry soil. They also resent being overcrowded so it's important to thin them out as soon as possible. Provide the brightest spot possible in your house as light levels are much reduced in the winter which can stress the plants. Make sure the compost is fertile, adding liquid feed if necessary. I find coriander grows best for me in early spring or from July onwards (they are sensitive to day length) and have resigned myself to growing it at these times of year!

With regards to the slug problem - there aren't many plants slugs and snails won't eat! You can try picking the slugs off the leaves and stems at dusk when they are at their most active. Although this can seem laborious it is very effective. You could also use an organic product called Nemaslug which you water into the soil. It contains nematodes (tiny parasitic creatures) which infect any slugs in the soil and kill them. It remains effective for about 6 weeks and is perfectly safe to use on food crops too (it is not harmful to humans, pets or wildlife). Beer traps are also effective at drawing the slugs in and drowning them. Just cut the bottom off a lemonade bottle and sink it into the ground so the top is level with the soil surface, and then simply fill the trap with beer. Other similar traps can be made by placing empty grapefruit skins or melon skins upside down on the soil. Slugs love to gorge on the sweet, aromatic flesh of fruit and the darkness and moisture suits them well. All you have to do is check the skins each morning and destroy the slugs hiding in there! For a long-term solution try to encourage more birds into your garden, they are excellent at removing slugs!

Aidan Vardy

Hi Carly, I have two [approx 15 year] beautiful rhododendrons that are in way of building of new shed. When is the best time, and how should I move them to a new site where I have other rhododendrons, with thanks Carly. Aidan Vardy.

Hi Aidan, you can move Rhododendrons successfully, however with such a mature shrub you will need to take care and remove as much of the root ball as you can. It would be best to wait until late March before moving your Rhododendron so that the soil has warmed up slightly. Avoid moving them any later than April as the weather will become too hot for them to cope. You can also move them in September/October. If your shrubs are large I would reduce the size of them by about a third as this will help them cope with the move, although you will lose flowers this year. Reducing the leaf mass will reduce the amount of water lost through transpiration. Prune in early spring, just above a set of leaves or above a node.

Prepare the new planting hole before you begin lifting the Rhododendron from its current position. Make sure you water the shrub well the previous day and tie in any stems that you can to avoid damaging them during lifting. Choose a cool overcast day to prevent the roots from drying out too quickly. Give the main stem a wide berth and aim to lift as big a root ball out as you can manage so as not to disturb the roots. Be prepared for the root ball to be three or four foot wide and about a foot deep. Any large roots that cannot be lifted should be cleanly cut with a knife or saw. Wrap the root ball in a damp hessian sack to hold it together and prevent the smaller roots from drying out. Re-plant the Rhododendron in its new home immediately. Dig plenty of organic matter (well rotted manure or garden compost) into the new planting hole. Firm the plant into its new hole and water well every day, especially in dry periods until the plant has re-established. I would also recommend mulching around the plant as well to retain moisture at the roots.

When moving mature plants there are no guarantees that they will survive. You could wait until autumn to move your shrubs and take cuttings from fresh new growth this summer - just in case! Although cuttings would take some years to reach the size of your large Rhododendrons, a small, younger plant will establish in the new position quickly and easily. I hope this helps Aidan.

Cathy Johnson

I'd love to know what is nibbling my rosemary, it always looks so tatty, whatever it is just nibbles a little from every leaf! - Any ideas Carly?

Hi Cathy, it sounds like you have rosemary beetles, which also happily nibble on lavender plants and sometimes sage and thyme. These little beetles are an attractive shiny green with purple stripes down their backs. Their eggs and white-grey larvae can be found on the underside of the leaves. They can even remain active over winter during warmer periods!

You can remove rosemary beetles by hand if you like to garden organically. The best method is to lay some newspaper under the plant or an upturned umbrella and gently tap the branches to dislodge adults and larvae. Alternatively you can use chemical sprays which should state on the label whether they are suitable. Look for the active ingredients pyrethrum, acetamiprid, deltamethrin or thiacloprid. Take care when the plants are in flower as these insecticides will kill bees too! It's best to apply pesticides in spring or early autumn. I hope this helps you resolve the problem, best of luck.