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June 2008

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Evergreen antics, roguing narcissus and cutting back in spring

Several shrubs or small trees that are normally evergreen can shed leaves during a cold snap to reduce transpiration. Some cotoneasters and Daphne bholua are in this catergory and became deciduous to tide them over a hard spell. In contrast I have noticed that many philadelphus cultivars, normally deciduous, have not shed their old leaves over the last few mild winters.

In spring I checked stocks of narcissus and snowdrops for symptoms of virus, fungus or eelworm, looking for symptoms such as marked loss of vigour and flowering, striped yellow and green patterns on leaves and curling of leaf blades. This is important particularly where a garden holds large numbers of bulbs and or

Some cotoneasters and Daphne bholua are in this catergory and became deciduous to tide them over a hard spell

Some cotoneasters and Daphne bholua are in this catergory and became deciduous to tide them over a hard spell

collections. Careful and thorough observations early in the year -before the symptoms are masked by high temperature levels and growth - on cloudy days followed by prompt roguing out and destruction will be invaluable in eliminating or halting spread.

Narcissus yellow stripe virus, spread by greenflies, is probably the most common virus affecting narcissus and has been worst on cultivars with Narcissus cyclamineus as a parent, such as ‘February' Gold and ‘Jenny'. While most narcissus can tolerate one virus, they will quickly deteriorate if two or more different viruses are present. I have seen some snowdrops with similar symptoms such as loss of vigour and poor flowering and these have been promptly removed.

These symptoms, however, could also be due to eelworm which also attacks narcissus, snowdrops and scillas and has a very wide weed host range. Basal rot caused is easily identified and as its name suggests there is rotting of the base of the bulbs with very few roots and they can be easily lifted.

Degeneration is a progressive deterioration that can occur in narcissus and results in reduced flowering or production of flowers of an inferior quality. ‘Grassiness' or ‘broodiness' are two names given to such conditions. The first name suggests the foliage becomes grass-like with many small offset bulbs and flowers distinct from the type, while in the latter the flowers become smaller but true to type. Again these can be rogued out easily and this condition is not caused by a pathogen. Lack of flowering can be due to other causes also, such as over-crowding, shade, dryness of soil and dept of planting. It is a good practice to lift, divide and discard weak or diseased bulbs every five years or so.

Narcissus yellow stripe virus, spread by greenflies, is probably the most common virus affecting narcissus and has been worst on cultivars with Narcissus cyclamineus as a parent, such as ‘February' Gold and ‘Jenny'.

Melianthus, santolinas, lavenders, sage were all pruned in spring to generate new growth as were ferns and epimediums. Annual pruning or cutting is a must for these plants to keep them looking neat and rejuvenated and it also increases longevity. The old flowering stems were taken from many herbaceous plants too - these also serve as markers for their positions in winter - such as delphiniums, rudbeckia, geraniums, aconitum and hostas. These are regularly divided and replanted at this time also to maintain vigour.

It is also an excellent time to divide and replant alpines such as companulas, moltkia, orchid, aubrieta, dwarf phlox, inula and dianthus, and many others. And the dianthus can be propagated by tip cuttings after mid-summer also. Several shrubby plants have responded well to pruning in spring also if they become over-grown, or outgrow their spaces, in particular hypericum, spiraea, aucuba, Rubus ‘Benenden' and daphne. I prune hard the deciduous Cornus alba ‘Sibirica', Rubus thibetanus and species of willow to get the highly coloured stems for the following winter. All of these plants that were cut back are now showing fresh new growth and fine foliage effect.

 

 

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