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Greenhouses

If ever there was a busy time in the greenhouse, it is early summer. During May the staging (what gardener's for some reason call shelves or tables) is full of seedlings and there is little room for anything else. On the whole the greenhouse is unheated because the electric cable doesn't stretch down the garden to the greenhouse, and try as you may, it is really difficult to get paraffin for more old fashioned kinds of heaters.

All of this, on top of the irregular Maytime weather means that greenhouse gardening can be quite difficult at this time of the year, so here are a few tips about getting round some of the difficulties.

Heating

If your greenhouse is unheated, there are a number of things you can do to keep your precious seedlings in prime condition.

If you have no form of heating at all in your greenhouse, night lights, those little candles, make great heaters. Simply dig a hole, about six inches deep, into which you pop a lit night light. You can cover the hole a little with a piece of brick, so no light escapes into the garden. Four night lights will keep an average six foot greenhouse frost free.

A Good Path

Do you remember night storage heaters? The idea was to heat the rock in the heater at night when electricity was cheap and let the 'heater' give off it's heat during the day. The only problem with them was they didn't stay warm for long enough - in my opinion. Well, a good greenhouse path works just in the opposite way.

Make your path with a good layer of builder's aggregate, then a layer of sand, and on top of this your concrete paving stones. The greenhouse is around 7 to 10 degrees warmer than the outside air temperature during the day. This heat is absorbed by the path, which will give off its heat through the night.

It means that a crisp clear day that reaches 12 C during the day and -2 C at night will never actually be frosted in the greenhouse.

Another trick we old gardeners used to do was place potted plants on the path at night, it will be the warmest part of the greenhouse.

Water

I was always taught to keep a watering can of water in the greenhouse. It's always worth the bother, because it warms to the same temperature of the plants.

It is really important that your plants have a constant temperature for growing, especially now when they are just getting established. If, when watering, you douse them with cold water the shock will shut down the metabolism and it will take a while for it to recover.

It might not show now, but believe me, when the plant is mature, it will be more susceptible to infections, especially fungal ones, if they are mistreated right now. Water with warmer water, but don't soak the leaves and don't over water either - that will lead to the horrid fungal infection called damping off.

Gardman Louvre Vent
Gardman Louvre Vent
RRP 34.99  33.99

Ventilation

This leads me smartly on to ventilation. A good breeze blowing between the new plants keeps damping off at bay, because more than anything, fungal infections need warmth and moisture to take hold.

Every greenhouse should have a ventilation window (often called lights for very old reasons) which is there to allow excess heat to escape from the roof of the greenhouse. This should be allowed to open on warm days, and if we're lucky this year we will get some pretty hot days. If the temperature reaches 15 C outside, it would not be uncommon for 30 C inside! If you have an automatic opener, check it is working - a cup of hot water held near it for a few minutes will open it.

If not, at the height of the day, if it is warm, shirt sleeve order as we used to say, then open the window a little to control the heat. Don't forget to close the door at night time, around 7 pm is best, to give the plants chance to settle down to a good night's sleep.

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