Postbag edition at Sparsholt College
Eric Robson chairs a postbag edition from the GQT potting shed at Sparsholt College with Chris Beardshaw, Anne Swithinbank, Pippa Greenwood and Rosie Yeomans answering listeners' questions sent in by post, email and Twitter.
Produced by Howard Shannon
A Somethin' Else Production for BBC Radio 4.
Q. What would be the best way to encourage a Eucalyptus Pauciflora Debeuzevillei to form multiple stem? Should the current, single stem be cut back and if so, when? How should cuttings be taken?
A. The younger the plant is, the easier it is to encourage it to produce multiple stems from the base. Pruning should be carried out in June, removing around half of the total height of the plant. Carry the pruning out in stages, especially if it is an older plant. Ensure that the plant has enough moisture. Eucalypti are best propagated by layering, or from seed.
Q. How can manhole covers in a lawn be disguised?
A. There are planters available designed to fit over manhole covers. A decent-sized planter will be heavy, but bases on wheels could be used to move them easily. Informal beds could be created around the manhole covers, with Sun Roses (or Rock Roses) such as Helianthemums, or other ground plants such as prostrate conifers, planted around. Alternatively a path could be created across the lawn that crosses the manhole covers.
Q. What can be done with the multi-purpose compost left over from growing potatoes either in potato bags or large pots?
A. This could be used for planting bulbs, sweet potatoes, salad crops or carrots. Anything from a different family to potatoes (e.g. - not tomatoes, aubergines, peppers or normal potatoes) can be grown. The fertiliser content will be very low after growing potatoes, so the fertility will still need to be improved. It would also be a useful mulch for borders.
Q. How can a wayward Gunnera be removed from a garden and the surrounding area?
A. Use machinery! Herbicides will work on the young shoots, late in spring. To prevent the plant from spreading, cut the flowers out and prevent the plant from setting seed.
Q. Could worms in a worm bin or compost bin overdose on caffeine and tannins from tea and coffee?
A. Use a small amount of lime to keep the acidity levels of a wormery low. Coffee grounds, citrus peel and onion skins should not be added. Even in a regular compost bin, large amounts of coffee grounds or tea leaves could upset the pH balance of the compost.
Q. What is the best method for preventing ants nesting in flowerpots, regardless of content?
A. Ants do not like water, or lime. Standing pots in a 'moat' of water may help - place a deep saucer of water under the pot, with the pot itself resting on pot feet or similar to prevent over-watering. There is also some evidence to suggest using a tea or essential oil of Black Peppermint or Pennyroyal will also dissuade the ants from coming near the plants.
Q. What is the panel's opinion on the theory of watering in a solution of shredded onions to a site on which basal white rot is endemic in order to kill off the rot?
A. The evidence for this technique for white rot is not that good, although there are similar theories for other soil-borne fungi. In allotments this problem tends to be endemic.
Q. How many alpines can be planted in a wooden box planter 0.5m (1.5ft) square and how should the soil be mixed? The current soil is reclaimed compost.
A. Firstly, remove some of the soil and perform a mustard and cress test to check it will grow plants. If it is not contaminated, remove half of the reclaimed soil and replace with John Innes No. 2 and some sharp sand or Cornish grit. The pH balance depends upon the alpine - Rhodohypoxis, for example, likes a slightly acidic soil. Ensure water can escape from the planter, using crocks or shingle at the bottom. Seven to eight plants is probably a good start, but these can be thinned out over time. Echeverias are recommended.
Q. A 30 year old, 2m (7ft) tall Fatsia Japonica is showing new growth after two consecutive years of pruning, but also looks limp and pale-leafed. Is this a result of the pruning or the recent hot spell?
A. Fatsia Japonica is a shade-dweller, so it will not do well in direct sunshine. Provide the plant with shade and organic matter and take a number of cuttings as an insurance policy!
Q. How often can seaweed meal be reapplied to the base of plants (as a slug repellent) before the seaweed meal itself becomes detrimental to the plant.
A. Seaweed meal will raise the local alkalinity of the soil. However, most soils are fairly stable and unless the plant is particularly sensitive to calcium, this is unlikely to be a problem. There are other products on the market such as ground and composted sheep wool pellets or pine needles, which will be more stable in the soil and act as a good repellent.