WINTER-PROOFING YOUR GREENHOUSE

The recent cold snap has turned gardeners’ thoughts to the challenges of the coming winter months, particularly the importance of safeguarding their plants. A Greenhouse can serve as a vital sanctuary for tender plants during winter. It provides a shield from frosts, and with the addition of insulation and heating, can provide a controlled environment within which plants can thrive. Historic Greenhouse manufacturer Hartley Botanic shares some of the ways Greenhouse owners can keep their plants warm this winter. Hartley Botanic’s online magazine also offers a wealth of know-how when it comes to Greenhouse growing, seasonal tasks and ownership: Gardening Tips & News from Expert Gardeners – Hartley Botanic (hartley-botanic.co.uk)

1.      Use insulation

Reduce heat-loss by installing winter insulation over glazed areas. The most effective method is to use bubble wrap polythene, cut to size and fixed on the inside of the Greenhouse, close to the glass. This is a fiddly task, since the material has to be cut to fit, and it may take more than one person to install the insulation. Suppliers of Greenhouse accessories will stock clips designed to fix the insulating material to the glazing bars. Partial insulation is also possible. If you wish to protect plants in part of the house, but don’t want the arduous task of cladding the whole interior with bubble-wrap, section off part of the structure. You can separate it from the remainder with a polythene sheet, or a bubble-wrap curtain, and put vulnerable treasures inside the enclosure.

2.     Maintain a minimum temperature

In a Hartley Botanic Wisley 8, six pane Greenhouse, a 2.5 kilowatt electric fan heater can be set low, so that heat comes on only when the temperature falls dangerously low. You will need to take a few days to work out the ideal setting on the dial of the heater and to match this with overnight minimum temperature. To do this you will need a reliable ‘max and min’ thermometer placed among plants on the staging or fixed about a metre above the ground, well away from the heater. A night minimum of 4º or 5ºC is a safe temperature to maintain if you want to be safely buffered against severe snap frosts. If you want to run your heating on a tight budget, have horticultural fleece available to spread over vulnerable plants during excessively cold spells.

3.     Try soil-warming cables

One of the most economical heating systems is simply to warm soil, either in a bed, or propagation bench. Afterall, many plants just need their roots protected from frost. Soil-warming cable provides heat where it is most needed, at the roots, so even if top-growth is cold-damaged, the roots will survive. Cable is safe and easy to install and, with a thermostat, lets you control soil temperature more accurately. It is particularly useful for protecting young plants in cold times of the year. Its performance depends on the cable type, prevailing temperatures and how the system is installed, e.g. a 6m cable consumes 75 watts and correctly installed will sustain temperatures between 15°C and 25°C per square metre of covered bench. Cover plants with fleece or a canopy of translucent sheeting to retain heat.

4.    Invest in a mini Greenhouse

Keeping a smaller Greenhouse inside a larger Greenhouse can help focus warmth and extra protection on plants that need it most. If you want to heat a very small number of plants, concentrating extra warmth only within a smaller Greenhouse, is also much more cost effective. A small Greenhouse within a larger structure, will trap heat during the day and minimise heat loss at night. Using a smaller Greenhouse is also useful for plants which need higher humidity levels. Try Hartley Botanic’s Patio Glasshouse.

5.     Don’t forget ventilation

Ventilate the Glasshouse as temperatures rise on dry days, but keep ventilators closed on damp or foggy days, avoiding chilling draughts. High humidity in the Glasshouse encourages botrytis or grey mould, which is grey-brown and fuzzy in appearance. It spreads rapidly in damp conditions. Remove infected material, ventilate the Greenhouse whenever possible or use a fan to improve air circulation. There has to be a balance between the amount of light, heat conservation and ventilation – and this applies to smaller Greenhouses used within larger structures too.

6.     Use a propagator for vulnerable cuttings

Cuttings can be kept warm, and given extra attention, in a propagator. Using one will mean you don’t have to buy pelargoniums or plectranthus, year after year, and you can raise all your own vegetable plants from seeds, including tomatoes, peppers and aubergines. It will mean you can take cuttings of salvias, pinks and lots of other plants too. In very cold weather, cover the propagator with fleece or bubble wrap. Place your propagator and cuttings in the shadiest part of your Greenhouse to avoid them overheating. A warm day might dry them out if they’re in full sun, so check them regularly.

7.     And lastly…

Unless they are particularly tender, another idea is to put containerised plants under the Greenhouse bench and cover them with fleece.

All Hartley Botanic’s Glasshouses and Greenhouses are handmade, bespoke, and made to order. Customers interested in purchasing a Hartley Botanic Greenhouse should visit http://www.hartley-botanic.co.uk or call 01457 819 155 for more information.