by Marjory House.
Season extension with greenhouses is the best way to extend your growing season and increase yield, diversity and overall enjoyment.
Excerpted from our double certificate design course.
What is season extension?
In industrialised nations we have become used to being able to buy every type of fruit and vegetable all year round. When you grow your own, you quickly become aware of the limits to what you can grow in your area because of the seasonal nature of gardening.
Different crops are ready at different times of the year, with summer being the main season for the majority of crops. The further you are from the equator, and the higher your altitude, the shorter that precious summer season will be, and you may experience a hungry gap when few fresh vegetables are available.
Season Extension with Greenhouses
A super simple cloche or cold frame can work wonders for extending the season. But truly, if you want to create a beautiful, productive, inspiring, and multifunctional space on your site, you simply must build a greenhouse. Whether it’s a tiny makeshift hothouse you can barely stand up in, or a hundred yard high tunnel filled with mature trees, a greenhouse will increase the diversity, yield, and enjoyment of just about any site.
Top ten reasons to build a greenhouse:
Start seeds early (and late!) Many seeds need warmth to germinate and develop into healthy seedlings. If the growing season is short, getting ahead can make a big difference.
Protect tender perennials and grow exotic plants. Increase your yields by extending the range of plants you can grow in your climate!
Protect early blooming fruits (like apricot) from heavy rains. Flowers on fruit trees are often quite delicate and can be damaged by rain, wind or frost, resulting in big losses to your fruit crop for that year. Choose dwarf varieties and plant them right inside the greenhouse.
Covered space for propagation and transplanting projects.Some plants respond well to a bit of nurturing, resulting in stronger, healthier plants. And gardeners also respond well to a warm place to work on a cold day! Choose a corner of your greenhouse to double as a potting shed and you’ll spend less time carrying seedling trays around.
Channel heat into your living space in winter. Build a lean-to greenhouse built against the sunny wall of your house and enjoy the extra warmth in the house.
Indoor/outdoor space for messy projects. Leave an open area in a section of a larger greenhouse and you’ll find that you use it all the time, for all sorts of projects.
Zen gardens! There is nothing like a high-ceiling greenhouse full of blooming, tropical, edible, aromatic, and succulent plants. Build your own mini-arboretum and escape to it when you’re feeling down. A mentor of mine even had a tiny office in his greenhouse, where she would go to get away from the family and write.
Secure medicinal and high-value plants. A well-built greenhouse with a locking door helps keep both animal and human marauders from making off with your crop.
Increased humidity for mushrooms, aquaculture. Some greenhouse designs include extra moist, dark, humid zones for cultivating edible mushrooms. Aquacultures also enjoy a more humid environment, and doing something inside a greenhouse could also allow you to add powered pumps, lights, and other features.
Guest housing! Sleeping in the greenhouse when it’s full of plants is the best!
You can plan space for propagation (seed starting) in a larger greenhouse, or build something intended especially for getting a jump start on the season. For convenience, or for simple ergonomics, this should be a bench or shelf. Extra lighting can be installed and/or heat mats are needed in more Northern climates. In temperate climates this may not be necessary.
Generally your greenhouse should be attached to your home or nearby, in your zone one area, because you will need (and want) to go there every day.
Larger greenhouses used for preservation crops such as tomatoes, peppers, or fruit trees, should be placed in zone two, unless it is more of a kitchen garden, then it should stay near the house. On a larger scale it is possible to have all three.
When a greenhouse is in constant use throughout the seasons, in particular if it is filled with more permanent perennial crops, other factors need to be considered year round:
When choosing or designing a greenhouse or polytunnel, it is important to ensure there are sufficient doors and windows that can be opened on warm days. It is surprising how quickly it can get really hot inside, often way too hot for both humans and plants!
On the other end of the spectrum, (unless your greenhouse is heated in winter) if you live somewhere with extreme cold, or if you have particularly delicate plants, more heat can be captured by insulating the greenhouse with a double wall plastic or glass. Recycled bubble wrap can be used for small areas, and combining techniques such as white walls, rock mulches, and even a cold frame or some cloches inside your greenhouse, can make a difference to whether your plants live or die.
If you live in a zone with high elevations, where winter weather sets in early and the permafrost levels go deep, the most energy efficient way to capture heat is by digging well below that permafrost level, preferably into a south facing hillside. Then, make raised beds within the greenhouse using compost.
For most homestead type greenhouses, raised beds are a good option for efficiency, either filling them with a good quality, bought compost, or ideally with your own homemade compost. I prefer French double dug beds integrated with high quality, on farm made biodynamic compost. Others prefer no-dig beds.
Another option for very cold zones is to put heat coils under the beds. These can be heated by either geothermal heat or via a closed loop hot water system fed by a solar hot water heater, wood boiler, or on demand water heater.
Airflow is very important for any greenhouse situation. Air flow is linked to temperature control. When the vents are open, air flow increases. But what happens on colder days when the doors need to be kept closed? Not only do plants need C02 for growth, they need airflow to prevent molds and fungus.
TIP: The biodynamic preparation called 508 can help regulate moisture and keeps fungus down in the soil. It is quite simply Equisetum arvense (field horsetail). This is an ancient plant full of silica. Pick in Spring, dry, add one ounce dried equisetum to four gallons of boiled water. Let this concentration cool then put it in a bucket and let it ferment for a week to four months. Strain off the plant material and store in a glass jar until use.
In my experience, the best greenhouses and polytunnels include a pond. This helps with pest control because it provides habitat for predators, e.g. frogs. It also improves the air quality, so may be part of the answer to the previous question.
Because greenhouses and polytunnels are confined spaces, it is possible to turn them into exclusion zones. For example, Alice Gray of Tyddyn Teg, North Wales, has excluded slugs from the farm’s extensive polytunnels. She did this by laying a strip of bran all around the inside edge of each polytunnel. As long as the bran stays dry, slugs are unable to cross it, and as she laid it inside the polytunnels, it does stay dry. Then she applied nematodes within each polytunnel. These ate all the slugs inside the polytunnels, so the polytunnels are more-or-less slug free.
The main disadvantage of greenhouses and polytunnels is that the rain can’t get in, so plants do need to be watered regularly. Doing this by hand may be time-consuming, but it does mean you get a close look at the plants while you are watering them and may spot problems early, such as pests or mineral deficiencies.
However, irrigation systems are very useful, and can be designed to use rain water gathered from the roof of the glasshouse or polytunnel, or can be part of a wider system of channels from a pond or dam. Whether you use overhead sprinklers or soil-level drip feed depends partly on what you are growing: For example, some plants are more vulnerable to moulds if their leaves get wet, especially within a humid glasshouse.
Soil & Fertility.
You can plant your greenhouse plants in pots on the ground, on tables, or on landscape cloth. Or you can just plant directly into the ground. As always, consider your soil’s needs, and make specific choices based on the geography and climate of your area.
Within a rotation system, fertility is managed at least partly by the different needs and gifts of different plant families. For example, the pea and bean family feed the soil via the nitrogen-fixing bacteria in their root nodules. When planting perennials, in particular within the confines of a glasshouse or polytunnel, it is worth putting some thought into this before planting.
Do some research into the needs and gifts of different perennials and companion planting. Mulching works well, but remember it may introduce or encourage the pests you have just excluded!
Here are a bunch of examples of season extension with greenhouses in use in the temperate Willamette Valley of Oregon. Here in zone 8, a simple greenhouse can extend the growing season by two months on either end and makes a huge difference in our annual yields.
If you need ideas and inspiration you could go find a greenhouse! This could be in your local park or botanic garden, or in a community garden or on a neighbour’s patch. Notice the differences between what is growing inside the green house and what is growing outside.
Re-visit the greenhouse at different times of the year, and in different weather conditions (e.g. on a warm sunny day and a cold wet day). What changes do you notice, both inside and outside the greenhouse? Talk to the gardener(s) and ask them what they value most about season extension with greenhouses.
This material is excerpted from the Aquaculture and Season Extension module of our double-certificate design course.
Further reading on this topic:
The Year Round Vegetable Gardener, by Niki Jabbour. Niki is located in Halifax, Nova Scotia. She gardens year round in the cold north and hosts a weekly talk radio garden show.
Pool, Kristin. Introduction to Season Extension in Organic Vegetable Production Systems
#seasonextension #greenhouses #freepermaculture #permaculturewomen #seasonextensionwithgreenhouses
Marjory House has been gardening and farming in the Willamette valley of Oregon for over twenty years. She currently owns and operates a seven acre farm with over 450 apple trees, and over an acre of vegetables grown for restaurants, farmers markets and Serro biodynamic seed company. She has maintained a fruit tree pruning business for fifteen years and a biodynamic consulting business for the last seven years. She can be reached through her website www.gobiodynamic.com .
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