Consider the water supply to the greenhouse. You will be surprised how much water you will require during June, July and August, just to keep your tomatoes happy. If you were watering by hand with a watering can, you would have to visit your Greenhouse every day to ensure that they did not go short of water.
A watering can will be required to water plants in pots, and you will need a watering
rose attachment to water delicate seedlings.
Always remember to fill up your watering can before you leave your greenhouse at the end of the day. This will allow time for the water in the watering can to reach the temperature of the greenhouse and prevent the plants getting a thermal shock when you water them.
A connection to an outside tap, via a long piece of garden hose, would be handy if the greenhouse was within a reasonable distance of the tap.
It is more environmentally friendly however, and will save a lot of carrying on an allotment, to collect the rainwater falling onto the greenhouse with guttering and a down pipe, and store it in a water barrel or two, joined with a siphon. From there it is possible to use another siphon and gravity and narrow gauge plastic tubing ending in plastic valves or “drippers”, to convey the water directly to the plants. Due to the lower “head” of water, being the height of the water surface above the grow bag or pot, which obviously reduces as you use the water in the water barrels, it is not as reliable as a mains water supply. However, with careful adjustment of the valves, it will keep your plants watered for several days, before you have to refill the barrel. You should empty your water barrels once a year to get rid of all the dust, leaves and debris, that ends up in the barrels after falling on the roof.
Remember, a beautiful butt or two could be the answer to your drought problems!!
Construction of a siphon. For those of you that did not pay attention in your science lessons at school, here is how to make water apparently flow uphill!! Place the two barrels, that are to be joined by a siphon, side by side on secure foundations. Fill one of the barrels. Take a length of plastic hose pipe, long enough to reach to the bottom of both barrels over their rims, and then completely immerse the pipe in the full barrel, allowing all the air to escape. Place your palm firmly over one end of the hose, while still under the water surface, and quickly pull the end of the pipe into the second barrel to below the water level in the full tank. Now take away your palm and the water will flow uphill, over the barrel rims, and eventually, the water levels in both barrels will equalise.
Set-up of plastic dripper valves. Fit a filter mesh (from a washing machine connector) to prevent debris being sucked into the narrow 7 mm plastic pipe. Immerse the pipe till just above the bottom of the barrel, lead it over the edge of the barrel, down into the Greenhouse, and fit the valves to the pipe at each plant position, using scissors. Once the water flows, suck on the end of the 7 mm plastic pipe if necessary, adjust the valves to give a slow drip rate. It can be a bit fidely to get the flow just right, but it is worth it so that you do not have to visit the greenhouse every day to do the watering. Do not set the drip rate too high, or you may find the barrels empty the next morning with their contents on the greenhouse floor!!
The approximate cost of the materials bought separately is; 5 valves £2.50; 10 m of 7 mm plastic supply pipe £5; pipe holder pegs 10 for £2.50. So the cost for enough materials to water 10 plants would be about £12.50.