Facebook Questions and Answers for the 11th October 2012

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

Eric Bray

When is the best time to prune buddlejas back, to stop them getting too big and straggly?

Hi Eric, the best time to prune most Buddlejas (e.g. Buddleja davidii) is in early March once the worst of the winter weather is over. There are some species however that are best pruned in the summer just after flowering e.g. Buddleja alternifolia, B. colvilei, B. farreri and B. globosa. In both cases, start by taking out any dead, diseased or badly damaged stems. For most Buddlejas you then simply prune all the remaining stems right back to a low framework (about 30-60cm from ground level). It's a good idea to carry out pruning annually in the spring, shortening the previous season's growth back to 2 pairs of buds from the permanent framework. Buddlejas grow fast and this harsh pruning will produce the best overall shape and flowers each year.

For those mentioned above that require summer pruning, they flower on the previous year's growth so don't need such a heavy prune. Cut back flowered shoots to strong buds and on old plants you can also take out a quarter of the oldest shoots completely to the base, to promote replacement growth. I hope this helps Eric, best of luck.

Pamela Alletson

How do I store geraniums over winter and when do I plant up next year?

Hi Pamela, half-hardy bedding geraniums (Pelargoniums) can be successfully overwintered provided they're kept frost-free and the compost is kept on the dry side. If they're planted in the ground then you will need to gently dig them up taking as much of the root balls as you can, and replant them into pots of multipurpose compost. Check the underside of the leaves for pests and treat any infestation as soon as possible, as they will quickly multiply once under cover. Water the plants and place them in a bright, cool (but frost-free) greenhouse or conservatory. A cool windowsill would also be fine. During winter keep the compost on the dry side to discourage rotting. You can plant them out again after the risk of frost has passed in May next year. I hope this helps Pamela, good luck.

Julie Goodwin

Hi. I've Autumn planted four varieties of Sweet Peas which have all germinated well. I have grown them indoors at around 25 degrees. Do I just put them straight into a cold greenhouse now until the spring? Or will they need to be hardened off? Many thanks as always.

Hi Julie, it would be a good idea to harden off your sweet peas so they aren't shocked by the cold weather (my greenhouse has reached very low temperatures this week!) Over the course of the next week put them outside for the day and bring them in at night - this should be sufficient time to harden them off for over-wintering in the greenhouse or a cold frame. I hope this helps, best of luck.

Maria Weaving-Gómez

Hiya! Me again. I collected a bunch of pansy and viola seeds from the ones I have planted all around the garden. I tried to sow some about a month ago but they did not prosper. When will the proper time for these to succeed, spring..? Any special instructions..? Thanks! :)

Hi Maria, the seeds of some plants (including some Violas) need a cold period before they will germinate - your seed may have been too fresh. The best germination will occur if you store your seed in a paper envelope or other dry container (moisture will encourage moulds) in a cool place such as a shed, garage or unheated room. You can then sow them from late February and you should have a higher success rate. It's also worth mentioning that if the seeds were collected whilst the seed pods were still green they may not be viable as they would have been immature. If collected when the seed pods were brown and crispy there should be no problem.

In the spring sow them in trays of seed compost and lightly sprinkle a thin layer of compost over them. Keep the compost moist and place the tray somewhere warm (about 18-20C), but not too hot as this could prevent germination. Once the seedlings are large enough to handle pot them up into individual pots or modules and plant them out when ready. I hope this helps Maria, we'd love to see a photo of your pansies and violas next year.

Ginny Lewis

I have a new greenhouse and was just wondering if I could plant some of the seeds I purchased cheap because the planting season ended in August? Have loads of flowers, herbs and vegetable seeds I'm itching to plant. I guess I just wanted to know if I can go ahead and plant anything I like at any time of year now that it's under cold glass in a propagator, or whether I still have to adhere to the packet's planting times, thanks!

Hi Ginny, what a great addition to the garden! There are some seeds you can sow now but unfortunately a lot of seedlings would fail to thrive in an unheated greenhouse over winter - partly due to temperature but also due to light quality and shorter days. Plants have complex ways to detect daylength and other environmental changes - it helps to signal when conditions are favourable for growth and flowering, amongst other things. Much breeding work has been carried out to produce flowers and vegetables which will grow outside their normal season e.g. winter lettuces and winter pansies.

The types of plants you could sow now in the greenhouse include perennial plants such as Aquilegia, Oriental poppies, Hellebores and Hollyhocks. Depending on the temperature they may germinate this year and remain small until spring or they may not germinate at all until next spring. You can also sow sweet peas now for planting out in the spring. Some salad leaf mixes are designed for autumn sowing in a greenhouse, along with some varieties of lettuce, parsley, chervil, cauliflower, peas and spring onions. Do check the seed packets to make sure they are recommended for autumn sowing! All other seeds I would wait and sow in the spring. The great advantages to having a greenhouse is the protection they offer to freshly pricked out seedlings in the spring, the improved and earlier growth of the plants and the ability to grow tender crops such as cucumbers and peppers. I hope this helps Ginny - best of luck with the new greenhouse!

Nicola Price

My Tropicana Black is currently in a pot, is this a plant that should be in the ground? Will it last the winter? I was wondering if Carly would also mind advising if my scharzkopff (not sure if that's the right spelling) will also survive the winter if I leave them outside. Thank you.

Hi Nicola, it looks like 'Tropicana Black' is a variety of Canna with purple-bronze foliage and scarlet flowers, and 'Schwarzkopf' is a variety of Aeonium with purple-black foliage (let me know if this is incorrect). Both these plants are half hardy so will require some frost protection over winter. Bring them indoors as soon as frosts threaten. I would recommend a bright windowsill in a cool room of the house, or a cool conservatory. Try to avoid placing them beside radiators and heaters. You can reduce watering so that the compost is kept barely moist throughout the winter months. Your Aeonium may lose a few leaves but should return next spring. Cannas may go dormant and lose their leaves if they experience very cold temperatures, but this is nothing to worry about provided they don't freeze and the soil is kept barely moist. Wait until all risk of frost has passed before moving them back outdoors next May. You can plant them in the ground but they'll need lifting each winter - I would be tempted to keep them in large pots (minimum 30cm diameter) as both are well suited to container cultivation and it saves you the hassle of lifting each year! I hope this helps Nicola, let us know how you get on.