Three Season Growing
in an Organic Greenhouse
at Snakeroot Organic Farm
by Tom Roberts

At Snakeroot Organic Farm we have six greenhouses, three of which are discussed here. The largest (left) is a 27' x 96' commercial Stuppy greenhouse, the second (middle) is a homemade 22' square cedar pole frame greenhouse, and the third (right) is an Ed Person 14' x 60' commercial (metal frame) greenhouse. Only the first (gh1) is heated, with a Benjamin wood furnace (130,000btu).

In-ground raised beds comprise about two-thirds of the big greenhouse; the other third is reserved for the transplanting and potting operation. The beds are rejuvenated every few years by hauling in and spreading buckets of compost. The beds are rototilled once a year. Between the beds, the aisles are mulched with leaves and/or sawdust.

The big greenhouse is unheated from November to March. When we turn the heat off in November everything freezes at night, and this marks the beginning of fall greenhouse cleanup. We pull down the trellised plants, haul all the vines to the compost pile, and prepare the beds for their next plantings. There are seven raised beds, and the two edge beds (Bed Numbers 1 & 7) have garlic planted in them in December. We choose the two outer beds because there isn't as much trellising headroom there, and because—being next to the greenhouse walls—they are cooler, which garlic doesn't mind.

The rest of the growing season gets under way when we plant beet greens, carrots and a few hakurei turnips in February in the middle five raised beds. We have to wait for a nice sunny day and plant in the afternoon so the beds will be thawed enough to plant in. The seeds take a few weeks to emerge, and once they do they grow very slowly until we begin to heat the greenhouse.

We have settled on these two crops because they are in great demand when the farmers' markets open in May, and also because they do not bolt in the heated greenhouse of April. We have tried spinach, radishes, and lettuce, and while they grow well, the length of their picking window before they bolt is too short. We have been growing them in the unheated greenhouses with good results, as they are more cold tolerant than carrots and beets, which means they will actually do more growing when the temperature hovers around 40°-50°F.

Once the greenhouse is heated, we start tomatoes and cukes in flats to be transplanted into the greenhouse beds in April and all the early starts for field planting, like peppers, parsley, celery, celeriac, and early broccoli. Now the beets and carrots in the beds really take off.

When the transplants are ready to go into the beds in early April, we are faced with the problem that the carrots and beets are so big that the beds are pretty much invisible. So our harvesting efforts must be directed to opening holes in the canopy where we can transplant cukes (some years) or tomatoes (other years). Within about two weeks of transplanting, the plants need to be trellised, as they are becoming tall enough to start tipping over. We wind sissal baling twine around the plants, barber pole fashion, leaving the ends loose. That is, We don't tie a knot around the transplant's stem. The twine is tied to the greenhouse superstructure. A local organic dairy farmer supplies us with all the baling twine we can use, and each trellis string lasts several years.

At the same time, the heated greenhouse is also used for starting all our field seedlings: broccoli, cabbage, herbs, celery, winter & summer squash, cukes, onions, lupines, peppers, eggplant, and tomatoes. Although we can move some frost hardy seedling out of the greenhouse by early May, this still leads to quite a traffic jam for most of the month of May. We need enough room to be able to water everything, to trellis the cukes or tomatoes, harvest carrots and beet greens, and move flats to the garden for planting, and to keep on starting transplants.

Late May and June is a time of transition and constant transplanting, moving flats and pots around and out of the greenhouse, and trellising tomatoes or cukes. Trellising begins with the most prcocious plants in each row, and continues as others reach the "tipping over height" of around 18 inches. Trellising will now take up several person-hours each week until August, when the plants grow too tall to reach. They are then allowed to bend over and head back down.

Without trellising, tomatoes and cukes take up a much greater area per plant, and greenhouse space, being expensive, is at a premium. Untrellised plants are also more difficult to harvest, as the fruits hide under the leaves. In a trellised system, where you can walk on both sides of the plants, no fruit can hide and harvest is accomplished without bending over, at least not too much.

By mid June for cukes, or mid July for tomatoes, greenhouse harvest begins again. The first week we get about a half bushel twice a week, then for several weeks it is a bushel twice a week. These are weeks where there is high market demand so we recieve premium prices for these early crops.

The system is far from perfect. We still have several problem areas, and we are still working on tweeking the management of our in-ground greenhouse production. The first problem is that the carrots and beet greens growing in GH1 are usually completely harvested by early June, yet the field crops—planted in late April—have yet to reach harvestable size. This leaves an undisirable gap in our production. So we either need to get the field crops to come in sooner or dedicate more greenhouse space to their production.

Another problem is that growing a fall crop of cukes or tomatoes means sometime in July we need to remove plants that are still producing, but aren't as important now that the field crops are coming in. If we don't get the fall crop planted early enough in the summer, then fall production is minimal, especially so since the days shorten considerably after early October.

For irrigation, we have all the beds on drip tape from June to October while the tomatoes or cukes are growing. We roll up the tape each year during the November greenhouse cleanup. As the year begins we first water by watering can, then by hose once the well line has thawed. The disadvantage to hand-watering of course is the time it takes, but the flip side is that it allows the waterer to slowly walk the aisles and see how things are doing, monitor pest pressures, estimate harvest times, etc. Once the beets and carrots are all gone, we roll out the drip tape again for the year.

We understand that we have created a unique ecological niche in this greenhouse, one which is far separated in season from the one just outside the walls, but one which is also physically connected to it's surroundings once the outside season catches up and the doors remain open for ventilation. We allow some weeds to grow all season long, although we try to pull them before they go to seed. We typically have goldenrod, white clover, foxtail, field sorrel, lamb's quarters, jewelweed, chickweed, anise hyssop and poppies as weeds. This is our attempt to maintain a certain "wildness" in the greenhouse, the better to maintain pest/predator populations year round.

Although we have had no aphid problems in the greenhouse, we have had difficulties with two spotted spider mites, white flies, and of course cucumber beetles. (We have cucumber beetles in May!) Spider mites have been kept in check very well by purchase and release of predatory mites every three or four years. We have had limited success in controlling white flies with encarsia wasps and delphastus beetles. The cucumber beetles we hand pick in the cool parts of the day, sometimes several times a day. This year we are going to incorporate Hb nematodes and beauvaria fungus in the soil to attack the larvae.

Garlic scapes beginning in May. By early June we are selling garlic scapes; by July we are selling garlic bulbs.

May beet greens in greenhouse, with a flat of small pots in the aisle nestled up against the bed.

Deena at planting table, with trays to do stacked high.

Trellised cukes with flats in aisle in early May.

Table of seedling flats.

The first cucumber blossom in May. Notice the carrot tops all around the cucumber plant; by the end of the month these will all have been harvested.

And cukes a-growin' a few days later.

Tom standing among the trellised cukes in June. By July these are about nine feet tall, and have reached the tops of the trelis strings.