Cold snap could damage thousands of popular plants warns College expert

January 2010

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(NOTE: This is an archived press release.)

Take action now to protect Mediterranean-style plants or risk losing them is the advice from the UK’s longest established and largest training provider for the horticultural industries, Writtle College in Essex.

Senior Lecturer Mick Lavelle has some top tips for gardeners to help secure plants associated with aspirational patio living and barbecue lifestyles that have soared in popularity during many years of milder conditions.

During this period of exceptionally prolonged freezing conditions with forecasters predicting at least another seven days of sub zero temperatures, gardens with a tropical look and feel are at risk of seeing their plants suffer irreversible damage.

Mick suggests the following top tips to help keep vulnerable plants safe:

• If possible, bring potted plants inside – Most palms and conservatory plants such as bay laurel (Laurus nobilis) angels trumpets (Brugmansia), olives or ornamental citrus trees, fare better if the minimum temperature is 5oc or above and are only able to cope with freezing conditions for a matter of hours at best

• Where plants are too large to move indoors, provide them with a protective wrapping made from a material such as horticultural fleece or hessian. Low growing specimens can have a chicken wire cage put around them that is filled with straw or dry bracken fronds to insulate them. You can even use shredded newspaper, but if you do, put a layer of old carpet or a tarpaulin over the cage to prevent the paper from becoming to wet.

• Smaller plants can be protected by covering them with a cloche, (if you have one) or by covering individual plants with a plastic bottle that has been cut in half, placed over the top of them

• Dormant ground level plants can be protected by covering them with a large plant pot filled with straw or similar material

• Shrubs and fruit bushes growing against a wall can be protected by draping them with fleece, attaching this with ties to the support wires or trellis they are growing on

• Line the interior of domestic greenhouses with bubble wrap, for a cost effective double glazing to protect truly tender specimens

• Bubble wrap can also be used to make a temporary shelter over your outdoor plants. Make a frame and wrap the plastic over this, securing it along the edges with waterproof duck-tape

• Remember also that even frost hardy shrubs or young trees may suffer if exposed for prolonged periods to northerly or easterly winds. These too will appreciate being wrapped for a short period if possible, and an extra, temporary stake, can prevent them being buffeted too much

• Thin barked trees such as birch and cherry, can suffer bark damage on sunny, frosty days, as the bark warms on one side (but remains frost bound on the other) and can split as a consequence. Wrapping them for the duration of a cold period can alleviate this and keeps these ornamental barked specimens healthy.

• When snow falls on a path, avoid using salt whenever possible. Shovelling it off is the best option and if a thin layer remains, a sprinkling of salt is enough to melt this. Only clear areas that you need to walk or drive on and remember that plants close paths and drives that get heavily salted are in danger of dying from a soil that is too alkaline. This is especially true of acid loving plants like heather and rhododendrons, but any plants tend to suffer if salt levels become high.

• Remove snow from branches of scale leaved conifers such as cypresses, or columnar junipers to protect them from splitting under its weight. If this happens, they will never recover their shape. If possible wrap them or tie them around their girth to brace the branches, thereby ensuring that the load of the snow is shared and therefore less likely to break branches

• Once the frost is over, you need to check that it has not caused your plants to be lifted in the soil. Frost heave as it is called, is caused by repeated freezing and thawing of the soil, that forces plants - especially smaller ones such as strawberries, shrubs, or young trees - to move upwards in the soil, sometimes even pushing them out of the soil altogether. This can break the essential, fine feeder roots and if they are not quickly replanted the plant can be severely injured or even die as a result.

Writtle College currently offers one of the largest horticulture degree programmes in the UK. Undergraduates are able to undertake specialisms in a wide range of horticultural disciplines. Horticulture courses at Writtle allow students to combine the theoretical principles underlying plant cultivation, with the practical and vocational skills associated with the horticultural industry.

Pictured: A tree fern on College campus wrapped up for protection during the snow and frost.