Tag Archives: Garden Greenhouse

Growing Tomatoes in a Short Season Climate

Montana is a challenge for those of us who love avalanches of delicious home grown and vine ripened tomatoes. Since the last frost here is around June 1 and the first frost in early September, or, horror of horrors, sometimes even in mid August, the season is painfully short. The plants can be grown outdoors, but even in the heat of summer, the nights are so cool it is difficult to get any tomatoes to ripen before frost hits.

I have evolved by trial and error a method that results in ripe tomatoes as early as June, which gives me a great summer crop of tomatoes. The first step in this solution was to get a greenhouse, which keeps the nighttime temperatures higher.

Mine is a 20’ by 40’ hoop house, so I have ample room to grow as many tomatoes as I could possibly want. I grow them directly in the ground as I found raised bins unsatisfactory. They dry out too fast and are hard to keep watered sufficiently, even after mulching. So, the plants now go directly in the ground, again with nice mulch to keep the watering more even. The mulch makes the angleworms happy too as they build soil quality.

Building a Hot Frame

Since I cannot afford to heat a rather drafty large hoop house in this climate, the next problem was how to raise the seedlings until frost danger is past. I first made a 4’ by 16’ foot hot frame by attaching a soil heating cable in evenly spaced loops to chicken wire.

The hot frame has sheets of Styrofoam insulation wrapped in plastic as a base enclosed with a box made from 1” by 4”boards to hold the next layers. I place a layer of sandy soil on top of the insulation, then lay the chicken wire with the heating cable, and to finish the sandwich, layer more sandy soil on top.

The current framework over the hot frame is a heavy wooden 4’ by 16’ bench with hardware cloth nailed over the top. I put uv treated 8 mil plastic over it draping down the sides to the ground. This still allowed enough light to make the oven effect dangerous, so I added a couple of old bed sheets on top of the plastic to filter the light better. In severe cold I can put old sleeping bags over it for additional protection.

Experimental Misadventures

Originally this hot frame was built in the hoop house. It had a metal framework with plastic over it and at night I put an incandescent light inside for additional heat. Covering the whole framework with the sleeping bags at night was the finishing touch. I figured it should keep the flats of plants alive even if it hit 20 below, which it can do here any time from October to March.

I was right. It went to 20 below for a few days and my min/max thermometer inside the hot frame showed it never fell below freezing. Unfortunately, I could not open the hot frame to water anything because it was so cold in the hoop house itself. All the nice warm plants dried up and died by the time it was safe to open the coverings.

The next effort involved lots of uv treated 8 mil plastic, my indoor show booth framework, plenty of 2” by 2”s, uv treated bubble wrap insulation, and countless rolls of electrical tape. I assembled an experimental and messy 8’ by 16’ tent like affair inside the hoop house. Then I moved the hot frame into the tent.

This meant I could have a heater in the tent section so I could water the plants in the hot frame during severe cold. This worked far better than I expected and the jerry-rigged tent lasted 4 years before the top gave way and started leaking so badly it became nearly impossible to heat.

The show booth contraption has been replaced with an 8’ by 16’ wood and insulated structure using double pane glass in the ceiling. I still use 8 mil plastic on the front and end so I can roll it up in the daytime to prevent overheating when the sun turns it into an oven. Keeping it inside the hoop house prevents damage from the nearly constant winds here.

Choosing Tomato Varieties

My choices after much testing for my growing conditions are Early Girl, which is mediocre in flavor but utterly reliable even in the cool fall, Park’s Whopper, similarly reliable but better tasting, Stupice, a Czechoslovakian tomato which is earlier than Early Girl and utterly delicious, a cherry tomato such as Sweet 100 or Sweet Million, and my most favorite tomato of all, Caspian Pink, a wonderful heirloom that is large and flavorful. Stupice and Caspian Pink do not do well in the fall when it is cooler in the hoop house but they are unbeatable in the summer.

Starting Seeds

Typically I start seeds 6 to 8 weeks before time to plant them in the ground. I use starting flats with dome lids for planting the seeds. I prefer the larger celled ones for tomatoes. The cells are filled with a mixture of 1/3 perlite, 1/3 vermiculite, and 1/3 sphagnum moss which has been evenly wetted.

One seed per cell of fresh seed is plenty. When using older seed, I plant two seeds per cell. The seeds are buried shallowly and I label each kind of tomato so I can identify them as they sprout.

After I have adjusted the controls in the hot frame so it is maintaining 70 degrees, the flats go into the hot frame, sitting on the warm sandy soil. As soon as the seedlings sprout, I immediately pot them up.

Potting Up

This is not standard practice for most people, but not enough light is entering my hot frame to actually grow stocky seedlings. I also do not want any damping off problems which those dome lids encourage. Each morning I transplant every new seedling into a little pot filled with Visser’s ph balanced potting mix.

I have tried all the brands of potting mixes available around here and hate all of them except Visser’s. I have almost 100% success with Visser’s but disturbingly more dead plants with anything else. I particularly despise the Miracle Grow mix.

I built two 2’ by 8’ benches that also go inside the insulated section. The heater, a small one from Charlies Greenhouse Supply, sits low to the ground at one end of these benches. I place the flats of transplanted tomato seedlings on the top of the bench near the heater. The hardware cloth top on the bench lets them heat nicely and they happily grow like crazy.

Desired Temperatures

I try to keep the temperature no lower than 50 degrees at night and no hotter than 80 degrees in the daytime. A min/max thermometer helps one to know what is happening to the temperatures when one is not in the greenhouse.


The baby plants need to be kept watered, which is best accomplished by bottom watering. Once a week I set each flat of transplants in a shallow plastic storage container which has water in the bottom and let it soak up into the pots until I see the top of the potting mix show dampness. Between the weekly bottom waterings, I mist them daily with a hand pump sprayer which does not damage the seedlings.

As the plants are tender babies, I never use cold water so I do not shock them. I keep buckets of water sitting in the heated section so I have a supply of greenhouse temperature water for the bottom watering, and I fill the misting sprayer with warm water in the house.

I have been using the Soil Moist crystals to hold water in the pots after the second repotting, which reduces my watering needs. I am careful not to use too many as per the directions on the can.

Making Root Balls

Once my tomatoes are in their first pots my entire focus is to help them make a big root ball. If a tomato plant has a big root ball it will easily become a large plant that will be a great tomato factory.

After the plant has grown enough to fill the pot with roots, I pot it up into a taller pot, but about the same diameter. I drop the whole root ball to the bottom of the new pot and bury the stem with additional potting mix. I remove leaves if they are going to be buried leaving some leaves and the growing tip coming out the top.

The wonderful thing about tomatoes is the stem sends out new roots wherever it touches the soil, so I now have a little plant busy making a lot more roots. Even though it visually looks smaller than before transplanting, it will shortly be displaying exponential growth so patience is quickly rewarded in this process.

After they have filled their new pots with roots I pot them up into larger round pots that let me lay the root ball sideways in the bottom. This lets me bury a lot of stem in this potting. One has to be very careful not to snap the stem in this stage, they have to be gently eased into place, and carefully buried with more potting mix and Soil Moist crystals. The stem may not flex far enough to come up in the center of the pot, but as long as it has a little potting mix between it and the pot wall, it will happily grow more roots.

Sucker Removal

All of the tomatoes I grow are indeterminate, which means they will keep growing more and more leaves and stems. This can get out of hand in a greenhouse. Looking between the leaf and the main stem, one can find the new little shoots called suckers growing as the plant is getting larger. I leave one at the bottom of the plant that becomes a major main stem in its own right, so each plant has two main stems as the little shoot quickly grows.

I pinch off all the others. Otherwise, the plant puts too much energy into making more foliage instead of blossoms and tomatoes. It is surprising how many of these suckers one plant can make over a season. The dense tangle that can result also hinders air circulation in a greenhouse.

Feeding the Plants

The seedlings start with two leaves that aren’t true leaves but are cotyledons. Initially the seedlings are best nourished from the seed itself. Never fertilize seedlings at this stage as it weakens the plants.

The next leaves are true leaves and look like normal tomato leaves. Once the plants have these first true leaves I have found Algoflash for tomatoes to be incredibly useful. This is a supplement that is composed of minerals, not the damaging salts that are found in commercial fertilizers.

The stems of tomatoes grown with Algoflash are extra sturdy and the leaves a rich healthy green. The plants grow rapidly but with great strength. This sturdiness is vital because I am growing much larger plants than usually are being planted into gardens and they can be difficult to handle without damage.

If I wish to add any other fertilizer I may also use a fish emulsion even though the smell is not appealing. Planet Natural in Bozeman has a good offering of such supplies.

Planting in the Ground

By mid May I can usually safely start planting the tomatoes in the ground in the hoop house. I use a propane heater when I need to protect them from cold nights.

I dig a deep hole in the well prepared soil. I have been adding manure and other amendments to the soil each year. Green manure will burn the plants so I use only aged or composted manure. I have also added rock phosphate and compost. The grass clippings used for mulch also decay into the soil, further enriching it.

I remove the plant from the pot, which is the most difficult step as the plant is large and breaking the main stems lethal. I lay the root ball sideways in the hole, once again burying as much stem as possible, removing any leaves that would get buried.

I mix some bone meal with the soil that goes back in the hole to prevent blossom end rot. Blossom end rot is mostly caused by too much nitrogen in the soil, and all that manure adds nitrogen. I then fill the planting hole with the soil mixture.

The tomato plant takes a few days adjusting to the new conditions, quietly growing additional roots. Then it abruptly begins growing above ground in startling fashion.

I have permanently attached two nylon cords per plant to the framework of the hoop house above each plant. As the plant grows, I twine each main stem around a nylon cord until they are supported by it. I keep some slack in the cord because the tomato plant will use it as it grows upward.

I continue removing the suckers and soon the avalanche of delicious tomatoes is underway. Some of the Caspian Pinks grow so large one slice is bigger than a slice of bread, making wonderful tomato sandwiches. I can hardly wait to begin again this year!