Kim Wilde answers your gardening questions.
I have a black bamboo, which is growing in a large container in compost. It has not survived the winter very well, and its leaves have gone brown and crispy. What can I do?
Although hardy in the ground, a bamboo in a container can suffer from drought in the winter. Bamboos need regular watering all year round, including winter, when the evergreen leaves can be stripped of water by cold winds and its root system is unable to replace the moisture from frozen compost. If planting out in the garden is not an option, then I would repot. Other than dwarf and very slow-growing species, most bamboos will fill their pots with roots within two years, and if not repotted will deteriorate for lack of water and nutrients.
Divide the plant by sawing or chopping through the congested root ball. After division, remove old, thin and weak growth, and about 30%-50% of the top growth, which will concentrate growth into the new shoots, making them come through thicker and stronger. This is best carried out in autumn or early spring. Use a soil-based compost and add a slow-release fertiliser and water-storage granules; remember that, although bamboos have a high demand for water, they will not tolerate water logging.
A balanced liquid feed is recommended to keep plants looking their best.
Can I grow a mimosa in Edinburgh? I have a sheltered garden that gets afternoon sun.
Acacia dealbata is native to Australia and Africa and unlikely to thrive in Edinburgh for at least another 80 years, by which time global warming could have kicked in, providing a climate warm enough even for Scottish vineyards... but I digress. Another acacia, which is reasonably hardy and may be worth a try, is A. pravissima (Oven's wattle) - a small, weeping evergreen tree with masses of fragrant yellow flowers in spring. You could grow one in a container using John Innes No2, and place it somewhere in winter where the temperature does not fall below 4C. Alternatively, plant in well-drained, fertile soil in a sunny, sheltered spot and talk to it in an Australian accent.
I have a forsythia that I had to savage because it was choked by a neighbour's vine. It now consists of a collection of 5ft stalks with some foliage at the top. How can I get back its bushy appearance?
Neglected specimens can be cut down almost to ground level (about 30cm) in early spring, to promote new growth this summer. Leave one or two of the stems unpruned, so as not to shock the plant to death, then prune them next year.