IN spring my nelly moser clematis sometimes produces green flowers and then as the summer comes on they return to normal pink with a deeper bar. Can you please explain why this happens?

P RENTON

REG SAYS: Several members of the clematis group which we call the large flowered hybrids seem to suffer from this malady and nelly moser along with dutchess of Edinburgh are likely to be the chief offenders.

I do not think that any research has been done to determine the exact cause but it seems to be linked with cooler conditions during late spring and early summer and (dare I write this), plants which are slightly deprived of food or water.

As there is little that we can do to improve the early summer temperatures, apart from perhaps praying, we are left with trying to enhance the catering arrangements so that the plant is well fed.

Clematis are hungry plants with a good appetite for food and water so make sure that the root area is moist in early spring just as the new growth buds begin to shoot before applying a generous handful of rose fertiliser to the surface of the soil. Lightly tickle this in with a rake or with the careful use of a hand fork, followed by a light watering and then mulch with well rotted garden compost or bark.

This should set things up well but the plant would also enjoy some additional feeding from early July either by regular applications of liquid feed or by a single application of one of the controlled release feeds.

Sometimes a lack of potash in the soil is put forward as a possible reason for the production of odd green flowers so this is why I recommended the use of rose food which is particularly rich in this element.

As the pinkness of nelly moser flowers is prone to fading in strong sunlight it is often recommended for planting in shady positions including sometimes north facing ones. The problem here lies in the fact that the added coldness of north facing spots is likely to encourage the production of green flowers.

Perhaps I should mention that there is also another problem called green flower disease where the clematis plant concerned produces only green, distorted blooms all summer.

Yours certainly is not suffering from this virus related disease and, as there is no cure, any plant that does become infected should be dug up.

* Do you have a question for Reg? Write to Reg Moule Gardeners's Questions, Editorial, Worcester News, Hylton Road, Worcester WR2 5JX. No correspondence can be entered into. Reg Moule answers your questions courtesy of David's Nurseries, Martin Hussingtree.