New watering system for the polytunnel

We have several automatic watering systems in the kitchen garden: a network of soaker hoses in the two large glasshouses and two serving the polytunnel borders, along with micro irrigation for the chillies growing in the smaller glasshouse. These are attached to timers that turn on the water supply at set times and for set durations. They are in use from late April or May until the end of the season, when watering would otherwise take up a lot of time. Both the micro irrigation and the soaker hoses deliver water exactly where needed in a controlled manner. I tend to water infrequently outdoors, but the undercover spaces must be watered regularly, especially during the summer.

A soaker hose is generally the same diameter as a normal garden hose, but is perforated along its length so that water slowly seeps out. They are very useful running along the narrow polytunnel borders, where they water the tomatoes, sweet peppers, and onions, during the summer and autumn. Similarly, for the glasshouses where they water further tomatoes and sweet peppers, along with cucumbers, melons, courgettes, and so on. They are not so good, though, for the central bed of the polytunnel, which is planted with various crops, many of which are sown in rows across the width of the bed. This makes it difficult to route a soaker hose without interfering with the crops.

Micro irrigation comprises a large bore pipe, generally the same diameter as a normal garden hose, into which small bore flexible hoses are inserted where needed. These can be fitted with various sorts of drippers and sprinklers. I favour an adjustable nozzle so that I can regulate the water flow on a pot by pot basis. In our small glasshouse, which houses our collection of chilli plants during the summer and autumn, the large bore pipe is routed around the perimeter and the small bore pipes taken off to water all of the 44 pots that it usually houses. Micro irrigation is excellent in this situation, but not at all useful in the polytunnel.

This week, we added some overhead irrigation for the central bed of the polytunnel. I suspect that it is not so efficient as a soaker hose or micro irrigation, but it is the only sensible approach for the main bed due to the size and the sort of crops planted. It does have some advantages, though, as it can cool down the tunnel environment on a hot day and raising the humidity helps to deal with glasshouse red spider mites, which prefer warm and dry conditions. Our polytunnel came from Haygrove, but we bought the irrigation system from Robinson Polytunnels, www.robinsonpolytunnels.co.uk. This cost £34 plus delivery for a kit intended for a polytunnel of 35 feet in length. It comes with a good length of supply pipe, similar to that used in our micro irrigation systems, several elbows and straight connectors, various tap fittings and hose connectors, a valve, tie wraps for securing the supply pipe, and, for our chosen length, seven drop tubes with spray nozzles. I think this was good value for money and was entirely happy with the contents of the kit and the function of the system.

New sprinkler system attached to the ridge tubes of the polytunnel

Our polytunnel is twelve meters long, so a little over 39 feet. However, the main bed starts a couple of feet inside the tunnel, so a 35 feet kit was plenty long enough. Installation was fairly straight forward. First, the supply pipe is terminated with an end stop, then laid out on the ground. The pipe had a line running down it, which I used to help line up the drop tubes. The pipe was laid out along the ground and, using a tool supplied, holes punched into the tube and fittings pressed in at intervals of five feet. The tube was then secured to the ridge tubes of the polytunnel using the tie wraps supplied. At the supply end, the tube was cut to length and one of the elbows employed to bring the feed down alongside the doorway where, via the supplied valve, it was joined to a length of ordinary garden hose. This was taken to the main polytunnel water supply, where it was connected to a timer. We have half a dozen Hozelock AC Plus timers, controlling the soaker hoses and micro irrigation, and now the overhead sprinklers. There are other makes, and also other models from Hozelock, but we have always been happy with the AC Plus; it is a simple design, but with sufficient control over the timing and duration of watering. Over several years of use, we have found them to be reliable controllers.

It depends on the water pressure, but with our setup, the sprinklers tend to water the central bed, the paths, and the edge of the borders, so the soaker hoses are still needed to properly water the borders. To avoid wasting too much water, the valve was adjusted to reduce the flow until the sprinklers just covered the bed. In the past, I must confess that this bed has not been watered as consistently as it ought to be, but this system should address that. I will adjust the timer until it waters to some minimum level, and, when needed, I can manually turn on the supply to provide additional watering.

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