Installing an automatic polytunnel watering system at Plwmp
Last week we were setting up a WaterMate Pro automatic polytunnel watering system for Kim, in one of her First Tunnel polytunnels. She already had an overhead sprinkler system in place, but it was decommissioned because she’s working on an arid planting scheme and doesn’t want everything getting drenched.
The dual-zone WaterMate, with the option of both ground level irrigation and smaller sprayed zones, was a perfect fit. She doesn’t have mains electricity, or a tap at the polytunnel, so it had to be a solar powered, pumped system.
The nearest water store was an old, leaf-filled water butt a long way from the polytunnel, which could have worked (the WaterMate can pump from a fair distance away) but we decided to use a nearby roof with guttering, to position a new water butt much closer.
Step 1 – Tension wires
We ran a 2mm galvanized tension wire down each side of the polytunnel, using fencing tensioners to tighten them up. The wire is also secured to the hoops using cable ties.
Step 2 – Fitting the pipes
Next we ran out some 13mm LDPE irrigation pipe down each side, and over the top of the door. This was fixed to the wires using cable ties, and to the polytunnel frame using P-clips.
Step 3 – Fitting the controls
The water pump was mounted by the polytunnel door, underneath the water valves, ona wooden board. The control unit was screwed to the polytunnel timber frame.
WaterMate is a dual zone irrigation system, which lets you water on two different time schedules (perhaps lots of water for some plants, and less for others), or simply to extend the amount of watering area that a single pump can manage.
Irrigation zone 1
The first zone was connected up to the perimiter pipes, which had 4mm take-off hoses every 2 metres. In the take-off hoses we put 4mm inline taps, which allows Kim to turn various areas within the polytunnel on or off, depending on what is growing there at the time. Fitted to the take-off hoses were a range of adjustable drippers and shrubblers.
Irrigation zone 2
The original plan was to water the central bed of the polytunnel using the second zone and a ground level soak hose, but we decided to have a corner of the polytunnel covered by sprayers, for keeping seedlings and small plants damp in hot weather. A short section of 13mm LDPE irrigation pipe was run from the water valves and fixed to the polytunnel timber frame using P-clips. Four quick-fit black spray nozzles were fitted directly into the pipe, over a distance of about 3 metres, giving a well covered area.
Environmental sensing
The Harvst irrigation control unit uses timers, air temperature inside the polytunnel, as well as light (from the solar panel) and Harvst soil moisture sensors to determine when to water. Kim will be experimenting with the best combination of triggers for her watering, depending on what’s growing at the time, and the season.
More about Kim
Kim Stoddart, editor of Garden Organic, Organic Way magazine; runs Greenrocket polytunnel courses from her smallholding near Plwmp, in West Wales. She has also written a book with co-author Sally Morgan; The Climate Change Garden.
