QUESTION: I have a number of informally clipped box in pots and containers. Every winter they go orange-brown and remain fairly discoloured into spring. What can I do to make them go green again?

ORACLE: Box in pots and containers often suffer from discolouration of the foliage, especially in winter. Sometime the foliage becomes very olive green tinged with bronze; in extreme cases it can be almost orange. This is caused by nutrient deficiency, usually potash.

Scrape away a little of the compost and add a good handful of Osmocote or Vitax Q4. Top up the pots with John Innes No.3 and then give each plant a generous soaking with Tomorite. Repeat the Tomorite application in a couple of weeks and your box should soon be a healthy, green colour once again. Incidentally the right time to clip box is early June – traditionally on Derby day!

QUESTION: I have been given a lovely cymbidium orchid which has been gorgeous for several weeks. The flowers are now fading. How do I get it to flower again? I have a number of phalaenopsis which I am reasonably successful with. Do I treat it in the same way?

ORACLE: Cymbidiums differ from phalaenopsis in a number of ways. Firstly they are terrestrial orchids; in other words they grow in the ground, rather than clinging onto the branches of trees. Secondly they have pseudobulbs – swollen structures at the base of the leaves for the storage of water and nutrients. They thrive in cooler conditions than phalaenopsis, and they need plenty of light to ensure flower production. They also flower just once a year – usually in winter.

The secret of success is to keep your cymbidium in a cool, light position indoors after the flowers have faded. Water it regularly, giving it a good soak when the compost dries out, but do not leave it standing in water. Apply a soluble orchid fertiliser every couple of weeks. After frosts have passed stand it outside on the patio where it gets plenty of light but does not get completely baked by strong sunshine.

New growths that started to form at the same time as last year’s flowers will grow and develop to form full sized pseudobulbs. By September or early October reddish shoots with rounded tips should start to appear at the base of some of the bulbs – these are the new flower spikes. Move your plant indoors into a cool, light position and water as before. Avoid moving the plant as the buds are developing, this causes the flowers to be arranged awkwardly on the stem. If the plant fails to produce buds it is usually a result of insufficient light.

QUESTION: Does it really make any difference if I go to the trouble of dead-heading my daffodils and narcissi? Some authorities insist it improves flowering the following season – others seem to dismiss it.

ORACLE: A good question. If you leave the seedhead to develop then the bulb is putting energy into developing the seeds rather than the bulb which will produce next year’s flowers. However most of the development of the bulb depends on the leaves; these need to be left intact and kept in good condition for as long as possible.

They photosynthesise and pass nutrients down to the bulb which are stored for bud development and next season’s performance. The simple answer is if you have a few daffs, and have the time, then dead head. If you have lots, and other gardening to do, then do not bother. A great tip from someone who manages an estate with acres of daffodils: pass the hedge trimmer over them just below flowering head height – it works brilliantly!

QUESTION: I planted a callicarpa in my garden about three years ago. It was in berry when I bought it and although it seems to produce flowers, the berries wither and disappear without developing. It is planted in good soil; other shrubs thrive in this garden, so what is going wrong?

ORACLE: This can be a problem with callicarpa in the first couple of years after planting. However after that the most common cause is that the wood is simply not ripe enough. This is usually caused by insufficient light; in other words your plant is in a shady situation. Direct sun is needed to ripen the wood and ensure that the plant can support the developing fruit. If the stems are too soft they simply shed the berries.

Potash helps ripen the wood of deciduous shrubs. As it is a very soluble nutrient it is often washed away on well drained soils such as sand and gravel. Make sure that you feed your callicarpa with Toprose in spring, and if it is a wet season again in midsummer. This will encourage fruit set and ripening of the plant’s stems.

QUESTION: The late frosts of last spring caused a lot of damage in my garden, especially to rhododendrons and pieris grown in pots. How can I prevent the same thing from happening again this year?

ORACLE: The frosts we experienced in April and May last year were unusually devastating for that time of year. Of course, if you live in a cold area, the new growth of pieris is often clipped by frost. Fortunately the plants soon recover and produce a new too deeply. The crown of a plant should be no more than 2cm below the surface. If it is the plant may not bloom.

Rhododendron flowers are a different story; once they have gone that is it until next year. Both subjects are more vulnerable in an open position where they catch the morning sun; its bright rays on frozen petals and leaves rupture the cells causing instant damage. Often if they are left to thaw slowly in shade they sustain less damage. (The same is true of course of camellias).

So bring delicate plants near to the walls of the house and ideally give them a west or north facing aspect rather than south or east. In severe weather, if you know frost is expected, lightly cover them with horticultural fleece overnight; this should keep them from harm.