Hot houses
Wally Van Lier of Shamrock Gardens has suggestions if you want to build your own tunnel house. Photo: Sol Morgan.
Ever wish you could grow tomatoes for longer, get an abundance of greens over winter, or start seedlings early in spring? Then having a hothouse may be the answer.
I talked to two locals who swear by them.
Noel Riley has two plastic tunnelhouses to complement his vegetable garden. I asked him why he chose plastic over glass, and he explained that when he and his wife Kath lived amongst the Italian tomato-growers in The Wood in Nelson, he noticed the regular cuts the workers got in the extensive glasshouses. He thought, “better to be safe than sorry”.
Both of Noel’s are Morrifield kitset tunnels, 4 metres long by 2.4 metres wide and 2 metres high, with one door, roof vents and a window at the other end. “Make sure it’s a sunny day and you have helpers to pull the plastic over evenly on each side,” he says. As for performance: “They’re ideal for the first-timer, and are plenty big enough for Kath and my needs.”
The one closest to the house gets more sun, so Noel grows tomatoes and peppers from spring onwards. “And silverbeet over the winter, especially for the chickens. The second, slightly cooler house grows greens, broccoli, cauliflower, butter beans and carrots.” Noel is wondering whether to grow rhubarb in the shadiest corner. “Because the soil is quite heavy and moist then I think it’ll do really well.”
Noel adds compost, manure (horse and chicken), seaweed, some fertiliser like lime, and coffee grounds to his soil. Coffee seems to improve the texture, he says, and he has seen fewer slugs and snails. Growing plants are fed with liquid horse manure. The tomatoes are grown in alternate years straight into Tui organic compost bags. A trickle irrigation system supplies water in both houses. The tunnels are cleaned every year for better light over winter. The doors are left open in hot periods with a shade cover to prevent flying pests from entering. He also covers the tomato tunnel with shadecloth in the hottest periods.
Noel wondered what he could do to keep them warmer passively during the cold months, other than adding another layer of plastic. There are several options: a black drum or container of water will absorb heat and release it at night. Raised beds can be lined with black plastic as another heat sink. Build hot compost on one bed, or move the worm farm in during cooler months. Or put in bale of hay or straw and wet it with nitrogen-rich liquid manure or urine. As the straw decomposes, heat will be released.
Noel is so happy with his tunnels, he is thinking of getting another.
“We picked our last tomato at the end of July,” adds Kath with a smile.
At the other end of the spectrum I talked with Wally Van Lier of Shamrock Gardens. He grows cut flowers for the local market in several large tunnelhouses. Having built his own commercial tunnels in Auckland, he has suggestions if you want to build your own.
“Make a sturdy wooden frame and get plastic as it’s the cheapest, easiest material to use. Make sure the roof pitch is steep for rain runoff, and face it towards the prevailing wind”. That applies to single-pitch greenhouses. “Orientate them north/south to catch most of sun through the day”.
Wally reiterates the need to get the plastic as tight as possible. “Put up the plastic on a hot day and fix it down really well. It will give you years of extra life.” He also explained the importance of good ventilation. It’s recommended that 30 percent of the roof area is for ventilation alone. He suggests raising small hothouses onto a footing/foundation. He uses large sliding doors and windows to alleviate heat stress, so pests like whitefly are minimised.
Shelter is important he says, but issues with tree roots taking nutrients has led him to go for shadecloth windbreak (on the western side).
Wally also talked about how growing good soil grows good plants. He rotary-hoes in lots of compost, manure and organic matter prior to planting. Fertilisers are used minimally, based on the crop and soil testing. Compost tea as a foliar feed gives even healthier plants.
For commercial tunnelhouses, Wally suggests contacting Redpath. For other kitsets (both glass and plastic, try Eden, Easyshed and Hunkin Garden Products online.
Sol Morgan
