I promised a post about last weekend's Greenhouse Gardening Course this week, and here it is. Because of the way time has been this week, I have written it from memory, but I have three pages of notes (and if you know my handwriting, you know that's a lot) as well as a sheaf of handouts to go back over. It is my full intention to do this soon, so it's likely that this post will be edited somewhat in due course.
The most important lesson from the Greenhouse Gardening Course was the importance of Management when you are running a greenhouse. Prof Vandre described a continuum from growing plants outside to growing them hydroponically, and placed greenhouse plants somewhere closer to hydroponics than I might have guessed. So many aspects of the environment need to be kept in balance, and this doesn't happen automatically in the enclosed situation.
The Big Issues
So, before we even started thinking about common pest issues or what type of glazing material is the most weatherproof for the least outlay, we had to confront the basic issues of gas exchange, humidity, light and soil balance. Plants need carbon dioxide in order to photosynthesize, and oxygen in order to respire. There is enough atmospheric CO2 and O2 outside for them to do this, but once enclosed, adequate ventilation is crucial to ensure that these processes can take place. We were shown examples of ventilation systems that didn't cut it, as well as some better-designed ones: a lot more venting per square foot is necessary than one might think. Some large commercial greenhouses even have propane-fueled CO2 generators.
Atmospheric humidity and soil moisture are key management issues also. The most common follar fungal disease, Pythium, can only take hold if the leaves have a layer of condensation on them for a period of five hours or more. Inadequate ventilation and poorly drained soil can lead to overly rapid evaporation of soil moisture in the daytime, and then as temperatures drop toward evening this moisture will condense and coat the leaves in this undesirable way for the whole night. One point that might at first seem counterintuitive but actually makes good sense was that on a cloudy and rainy day, ventilation to the outside will still help to dehumidify the greenhouse: because it is warmer inside the greenhouse. Even if the air from the outside is moist, its relatively lower temperature will help to dry the air inside. To offset the cooling effect of outside air, as well as to avoid having too sharp a drop in temperature at night, the use of simple heat sinks was recommended, such as gallon jugs of water, that would absorb heat during the day and then release it into the greenhouse as temperatures drop.
Nowadays, there are many materials that have very good light-permeability whilst being UV resistant: but we learned that we needn't fixate on trying to get 100% light penetration. 60% is usually plenty. We discussed how to design the greenhouse so that the maximum surface area would be getting the sun as close to 90 degrees as possible for maximal effect. However, the importance of reflecting as much light as possible within the greenhouse was emphasized. All wooden surfaces should be painted white (latex paint is fine). Some people use aluminum foil or mirrors to bounce the light around within the greenhouse and thus maximize its availability.
For a balanced growing medium, Prof Vandre recommended 1 part porous material (like river sand or perlite (although the latter is so light that it tends to rise to the surface, and the general attrition of gravity means that you really want your drainage material at the bottom)), 1 part organic material and 1 part topsoil. He suggested retesting the soil and replacing spent nutrients at the end of each growing season, as well as checking that its porosity was still balanced, but emphasized that the soil itself doesn't 'wear out.' (I found this a little surprising, but if my method of replenishing the spent nutrients was going to be adding organic materials (one of the 'three parts' composing the soil medium), it seems like that could be viewed as replacing the soil. I guess it's a matter of definition.)
Various different irrigation systems were discussed: there are many that do not work! Drip irrigation is simple, inexpensive and effective. We also went into some detail about calculating the hydration needs.
Beyond the Basics
We looked at high-input, engineered strategies used in commercial greenhouses, had a show-and-tell of the most useful gadgets for a greenhouse manager (including a pH meter, and a light meter, whose unit of measurement is the delightful 'foot candle') and were shown a simple and straightforward test to measure soil porosity.
Many rules of thumb were gone over, as well as more complex algorithms for fine tuning these various axes of balance.
Main Take-Home Messages
The overarching message came through that providing one follows good management practices, the pest and disease problems notoriously associated with greenhouses should not arise: if they do, diagnosis is the key, and this includes diagnosis of which management area needs attention.
But the secondary message that really hit home for me was that plants grown in a greenhouse are much more tender than plants grown outside. They often only have a single outer layer of cells on their laminal surfaces. This leaves them much more vulnerable to sucking insects like aphids, to whom a greenhouse provides such a wonderfully hospitable environment anyway.
There's something about this that I find unappealing. I'm sure tender plants are delicious, but in my gut, I feel equally sure that plants grown outside, especially a relatively clean 'outside' like we have, are going to be richer in nutrients and character!
Why Do This Anyway?
There are two main reasons why people choose to have a greenhouse. One is to grow plants that otherwise could not grow at all up here; the second is to extend the short growing season - to add a little time at each end. The main targets for 'reason one' are tomatoes and cucumbers, for a big surprise, with peppers a close third. I'd love to grow some tomatoes, but I know that I don't prefer hothouse tomatoes. I know cucumbers are so good for you, but I don't especially care for them and nor does Phil. Everyone who knows me knows how much I love spicy peppers, but bell peppers make me sick and so do underripe spicy ones, which might be the best we could get here. For all the additional effort and management required to maintain a higher ambient temperature for those kinds of plants, I might be happier drying excess tomatoes from Phil's parents' farm in Oregon, where some years they grow like a riot, and having a supply of dried tomatoes that were grown in the hot, dry climate they prefer. Dried ripe hot peppers are also easily and cheaply available.
Perhaps it's unadventurous, but I am more drawn to growing plants that at least have a chance of doing well outside here. And it's only my second springtime here, but I know what a plethora of wonderful wild greens there will be about six weeks from now, and I want to make sure that I have some time to forage for those as well. Thus, I'd be more of a candidate for the lowest-possible-tech greenhouse that is purely designed to extend the season, not to make possible what would otherwise be impossible. Prof Vandre said that generally, homes make a poor substitute for greenhouses for seedlings at the beginning of the season because they are generally too warm and the light sources are too far from the plants. Our cabin tends to be chilly, and we've maneuvered lights right over the seedlings, so aside from space constraints, our home is probably better than most!
I asked specifically about a halfway-house kind of situation like having a movable polycarbonate cover that one could put over a raised bed early and late in the season, and was assured that this could work well, although whilst in use it would mandate similar managerial vigilance to a full-sized greenhouse. Another participant in the class told me of a system like this that he's been using successfully involving electrical conduits plugged into pieces of rebar with polypropylene stretched over - cheap and effective.
With everything else that's going on at the moment, I'm thinking that for myself, this halfway-house is the approach that I'm most likely to think about. On the basis of the class, I see that greenhouse gardening is an intensive labor of love the fruits of which might not be things that I value most of all. However, some of our other family members up here are interested in a greenhouse too, and I would love to share all the informative handouts and stories that I learned with them and to help out on a regular basis if they do choose to have a greenhouse this year.
The seedlings that we have started at the moment are: celery, basil, lavender, carrots, leeks, cauliflower, mache, radicchio, chives, spinach, dill, parsley, holy basil and maca. I'm going to start beets, peas and another rotation of greens and herbs pretty soon. We'll probably plant potatoes directly first week in June again also. I'm so excited about the maca!
These are all plants that can grow outside here in a decent year (with the possible exception of basil).
This year, I intend to consolidate my knowledge of how these kinds of plants do and use technologies like those cold covers and the raised beds we've been working on to extend their season somewhat (weather permitting!) whilst continuing to do some of the wild-crafted seed-sowing that we did last year and that both of us have always done (like gathering watermelon berries in August/September and sowing their seeds on bare patches for great greens in spring and berries in late summer, or sowing chocolate lily bulbs). Living as close to the bluff as we do, with the erosion situation as critical as it is, we also need to bear in mind the structural hazards of any situation involving a lot of water draining off, so we'll need to be very careful with that.
I hope that this is somewhat interesting and helpful to somebody!
Yesterday we had gorgeous blue skies and sunshine, the seedlings were outside all day. Today, it has been snowing (shading into sleet in lower areas) all day.
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a very skillfully written piece of creative nonfiction that tells the story of the discovery of AIDS, the recognition of its gravity, the horrendous suffering of the early victims, the heartbreakingly rapid spread, the efforts of the scientists to get the problem recognized and get something done about it, the regrettable human traits that tarnished scientific inquiry at many stages of the process. 