Greenhouse grow domeJuly 23rd, 2017. Post by Quinta do Vale
Why would anyone need a greenhouse in Portugal? Given adequate water and soil fertility, the climate provides more or less ideal growing conditions pretty much year round. General climatic conditions though are one thing. Specific microclimates are another. This quinta has mountain ridges to the south and west and doesn’t get much heat from the sun early in the year. As a result, the clay soils are slow to warm in Spring. Any summer vegetable planted out much before May tends to stand still and then take a while to get going again once soil temperatures rise, so peppers and aubergines frequently don’t get harvested until October and November. A greenhouse in the sunniest spot on the quinta would make a huge difference. I could grow plants from seed in early Spring, bring them on while the soils warm up, and overwinter those which can be effectively perennialised for an early start the following Spring.
I also wanted to experiment with aquaponics to find a way of growing vegetables intensively without the need for supplemental irrigation.
The completion of the geodesic dome greenhouse was consequently eagerly anticipated. The covers went on at the end of April. Seeds were sown and plantings made. And since then, I’ve been revising my ideas of how growing our food here can be achieved almost as fast as the plants themselves have been growing.
The beginning of May was a bit late to grow everything from seed, so planting began with some starts from the local market; mostly peppers and cucumbers, followed by sweet potatoes. Butternut squashes, tomatoes, chard, red cabbage, luffas and malabar spinach went into seed trays. The one surviving banana which made it through the -10°C temperatures of last winter outdoors and unprotected was planted in the central growing bed.
By the end of June, I planted up the aquaponics tanks. The system isn’t yet fully operational. I’m still trying to source a controller for the pump to switch between filling each group of 4 tanks in turn. It’s a simple routine, but unfortunately most irrigation controllers aren’t programmed with aquaponics systems in mind and are overcomplicated and insufficiently flexible to adapt to this purpose.
The siphons and drainage returns to the pond are complete and working. I decided, after a lot of trial and error, to abandon the bell siphons frequently used in aquaponics installations. Instead I’ve used U-siphons made from waste-pipe plumbing joints. In this set-up, I found that they start much more reliably and are more solid and stable than the easily-disturbed bell siphon assemblies.
I chose LECA (lightweight expanded clay aggregate) as the growing medium because of the millions of pores in its structure. This creates a massive surface area – many times that of gravel – for colonisation by the microbial ecosystem essential to healthy plants. To get the ecosystem going, I soaked the LECA with a 1:4 dilution of actively aerated compost tea in water. Until I get the pump controller sorted, the chard, tomatoes, red cabbage and lettuce get a nightly watering from the hosepipe and all are so far doing well.
At the same time as planting up the aquaponics tanks, I finished making the shade netting cover for the dome. This is multi-purpose: to prevent scorching of the plants by the midsummer sun, to keep temperatures a little cooler and to prolong the life of the PVC cover of the greenhouse.
So far, so good
I continue to be astounded by the rate of growth of plants in the greenhouse. This is what’s led to me rethinking some of my growing strategy for the quinta. The more of our food I can grow intensively in the aquaponics system and growing beds and tubs in here, the more of the quinta I can devote to perennial systems which more or less take care of themselves once the initial soil improvements and water retention earthworks have been implemented.
I’ve also been impressed with the healthy atmosphere in the geodome. Compared with polytunnels and conventional greenhouses, its extra height and lack of roof (for now) over the pentagon at its apex seems to be allowing for much better airflows. So far I’m not seeing evidence of fungal or pest problems. There’s been a shortage of squash pollinators – ie. bees – so I’m pollinating by hand at the moment. Future plans for the quinta involve bee hives on the slope above the greenhouse. I’ll also be encouraging wild and solitary bees into the greenhouse by planting more bee-attractive plants amongst the edibles and by providing habitat for them to set up home.
Previous posts about the greenhouse: