Greenhouse Gardening: Growing Hydroponic Tomatoes and Lettuce

An Illustrated Overview

By: Chris Delker

© Chris Delker, 2012 All Rights Reserved

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Intrigued About the Idea of Growing Greenhouse Tomatoes or Lettuce? Thanks for subscribing to my email list and downloading this free report. I hope you'll find this report and the weekly articles about greenhouse gardening I'll be sending you it to be both interesting and useful. Before I get into the nuts and bolts of growing greenhouse lettuce and tomatoes, I want to tell you just a bit about myself so you'll understand my perspective in writing this report. First, you should know that I'm NOT a hobby grower. I've been a commercial greenhouse grower for more than 10 years. And I've been involved in growing outdoor crops such as blueberries, peaches, cut flowers, etc. for much longer. So why do I have a website, backyard-gardening-fun.com, that's primarily oriented toward backyard gardening and backyard greenhouse growing? Because everything I've been involved with in commercial agriculture can be scaled down into wonderful hobbies for folks who just want to dabble on a part-time basis. Even greenhouse gardening can be perfectly suited for someone with just a modest backyard. And gardening is a hobby that so many people are getting involved with these days. Many just yearn for the connection with nature that gardening provides. Others, I think, are a bit concerned about the nutritional quality and safety of food that's mass-produced and shipped into supermarkets from all points of the globe. Whatever your reason for being interested in greenhouse gardening, I hope you'll be intrigued and maybe even a bit motivated by this report. Remember, too, that if you're interested in greenhouse gardening, there's a world of possibilities open to you. Though you're about to read an overview of growing tomatoes and lettuce in a greenhouse, there are countless crops that can be grown successfully in greenhouses, using much the same systems described here.

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OK, let's get started… A Wintertime Oasis Running a big greenhouse takes lots of hard work. But that work does come with some fringe benefits. Going inside the greenhouse on a cold winter’s day is like walking through a time warp; outside, it might be a frigid February day, but inside, it’s like a beautiful day in early June. So efficient is the greenhouse at capturing the sun’s heat (the “greenhouse effect,” don’t you know), that on cold, sunny days the temperature in the greenhouse is maintained in the seventies without running the heaters. In fact, even on the very coldest of days, the greenhouse ventilation fans will occasionally cycle on to draw in some of that frigid outside air, keeping it from becoming too warm inside the greenhouse. And not only does it feel like a nice spring day inside the greenhouse, it also looks it. While outside, the predominate wintertime color of dull brown prevails, inside the tomato greenhouse, the rich, emerald green of the leaves provides a background for the sprinkling of lemon-yellow blossoms; and the green, pink, and red globes of the ripening fruit adorn the plants like Christmas tree ornaments. Sometimes we use a hive of bumblebees to pollinate the tomato blossoms, and the sight and sound of the bees purposefully zipping from blossom to blossom help to complete the illusion of springtime. The tomato plants, 600 of them, are in rows that stretch almost ninety feet in length, and each plant is suspended from wires eight feet high. Walking the aisles between rows gives the illusion of being between two closely spaced green walls.

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The slight rustling of the leaves harmonize with the contented buzzing of the bees, and with the rhythmic bass thrum of the ventilation fans creates sort of a lullaby concerto. Given the soothing sounds and the pleasant temperature, it’s not a bad place to stretch out on the floor between the rows to grab a quick nap. (Not that I’ve ever been caught doing that!)

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The Set-up for Tomatoes There are a number of different systems for growing greenhouse tomatoes, but we have been successful using a hydroponic system. The tomatoes are grown in plastic pots filled with perlite. The pots are called Bato buckets, and we grow 2 plants in each pot. Our greenhouse is 30 feet wide by 96 feet long, and holds three hundred pots, for a total of 600 tomato plants. Each bag is watered with a spray emitter. The frequency of the irrigation is controlled with a timer, and nutrients are injected into the water with each irrigation cycle, so that the plants are fed every time they are watered. One of the great advantages of using a hydroponic system is that the grower has absolute control over the nutrients being delivered to the plants. All of the macronutrients and micronutrients that the plant requires can be delivered in precisely the quantities needed. This helps to ensure that the

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plants are healthy and productive. And it also helps to ensure that the tomatoes themselves are packed with the full range of nutrients (and flavor!) that tomatoes are supposed to have. Constant monitoring is required, however, to ensure that the proper quantities of nutrients are being delivered. The appetite of the plants will vary depending upon the stage of growth, and – just as with humans – the health of the plants may be endangered if they are underfed or overfed. At night, and on cold, cloudy days, the greenhouse must be heated. Though the tomato plants will survive as long as the temperature remains above freezing, they will not be productive if the temperature is allowed to drop below 60° F. From the low sixties to the low eighties is the preferred temperature range, and any significant excursions out of the comfort zone will result in reduced fruit quantity and quality. We use propane to fuel our greenhouse heaters, but it’s an expensive source of energy – and ever increasingly so. As with virtually any crop, tomato plants have plenty of enemies in the form of insects and diseases. The shelter of the greenhouse, though helpful, does not completely eliminate the potential of an outbreak of one pest or another.

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But the controlled environment of the greenhouse does permit the use of some weapons that would be less effective in the field. Sticky traps like the yellow and blue ones in the photo above are helpful in monitoring the pest population, and helping to control it to a degree. And beneficial insects are available to combat most any insect pest, and they can be extremely effective when used properly. We never, ever, spray the plants with so much as a drop of any form of pesticide – a fact that a great many of our customers appreciate. The Payoff The greenhouse tomato season begins in early September when the seeds are planted, and the first tomatoes are ready to harvest by Christmas. And, let me tell you – these tomatoes are GOOD!

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Greenhouse tomatoes don’t have a great reputation for flavor. In most cases, the tomatoes sold in grocery stores - greenhouse or otherwise - have been picked green and shipped great distances, and the flavor of these well-traveled tomatoes varies from fair to hideous. You might even have purchased some from your local supermarket (they're often labeled 'hothouse' tomatoes in grocery stores). If so, I hope you liked them. But unfortunately, I wouldn't be a bit surprised if you were less than impressed. But hydroponic tomatoes, with the advantages of being fed a precisely balanced diet, and allowed to ripen before being picked, will match any pampered garden tomato for flavor. Since we sell all our tomatoes locally, we have no need to harvest the tomatoes before they're fully ripe just so they'll survive shipping. And obviously, if you grow tomatoes in a backyard greenhouse, you'll have the same advantage of letting them ripen before you pick them.

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The result, I assure you, will be spectacular tasting tomatoes!

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Hydroponic Lettuce: A New Way To Grow An Old Crop

The hydroponic system we use to grow lettuce is really very simple, both in concept and in execution. We utilize a hydroponic method known as the nutrient film technique (NFT). In this system, the lettuce plants are grown in rectangular, flat-bottomed tubes. Holes are spaced in the top of the tube at eight-inch intervals, with one lettuce plant growing in each hole. (You can buy tubes ready-made for the purpose of growing hydroponic lettuce, but they can be rather expensive. We use guttering downspouts purchased from a local home improvement store (like Lowe's or Home Depot). We cut the holes with a hole saw, and use a heat gun to form the inlet and outlet ends.) Nutrient rich water is continuously pumped from a holding tank into one end of each tube. The nutrient solution flows from the input end to the drainage end, bathing the roots of the lettuce plants with a constant supply of both water and nutrients. The quantity of solution entering each tube is restricted so that only a very shallow layer, or film of solution is flowing through the tube. As it drains from the tube, the nutrient solution is carried by a gutter drain back into the holding tank, where it is re-circulated by the pump. In the wintertime, the nutrient solution is heated so that the root zone of the plants is maintained at an optimum temperature. The Set-Up We built the framework that supports the tubes from galvanized pipe purchased from a local fencing supply company. The framework must be assembled with precision to ensure that the tubes are supported with the proper gradient. The nutrient solution flowing through the tube must not flow too fast or too slow, and must flow at a steady rate throughout the length of the tube without any ponding.

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All air drawn into the greenhouse for ventilation is filtered through a fine screen, which helps to exclude insects. Any insect pests that do manage to become a problem are controlled with beneficial insects, just as in the tomato greenhouse. For most bad bug species, there is a corresponding good bug species whose favorite snack just happens to be the bad bug you are trying to eradicate. The beneficial insects are available through a number of commercial sources, and can be a very effective tool for controlling insect pests. We never spray so much as a drop of pesticide on our lettuce, same as with our tomatoes. The NFT system, in conjunction with the shelter provided by the greenhouse works quite well for growing lettuce. The enclosed structure of the greenhouse permits a certain degree of control over environmental variables such as temperature and humidity, which in turn helps to maintain a steady rate of growth. We’re able to harvest lettuce from October until it becomes too hot in early summer. Each time a crop is harvested, another crop is started to take its place, so that at any given time there are multiple crops growing in various stages of maturity. The Growing Process Each lettuce plant begins life in a 1-inch foam Oasis cube, which comes in sheets of 162 cubes. After being seeded, the Oasis cubes are grown on a propagation table, separate from the main NFT system. A timer controlled flood-and-drain system keeps the cubes moistened, and heat mats under the cubes maintain the ideal temperature for germination. The seeds usually germinate in two days, and are allowed to grow on the propagation table for no more than two weeks. The sheet of Oasis cubes is then broken apart into the individual cubes, and each cube with its seedling is placed in a tube in the NFT system.

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The seedlings are initially placed in tubes with the holes spaced only two inches apart, called nursery tubes. We've learned that some varieties of lettuce can bypass the propagation table, and be grown from seed in the main system. Other varieties are a bit less hardy, and will germinate more fully and evenly using the propagation setup.

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After spending one week in the nursery tubes, the plants are transferred into tubes with the holes spaced eight inches apart, called finishing tubes, where they remain until they are harvested. When the plants are transferred from the nursery tubes into the finishing tubes, the tubes are initially crowded together, with each tube touching its neighboring tube. When the plants have grown enough that they are beginning to touch plants in neighboring tubes, the tubes are moved apart to a spacing of six-inch centers, and then to a final spacing of eight-inch centers.

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Spacing the tubes progressively farther apart as the plants grow helps to attain maximum utilization of the greenhouse interior space, growing far more plants than would be possible using only the final eight-inch spacing. The Product When the lettuce plant is harvested, it is removed from the tube, and the long roots are trimmed, but not completely removed. The plant is then placed in a plastic clamshell or a plastic bag, which acts as a ‘mini-greenhouse,’ providing each plant with its own moist microenvironment. We call our lettuce “living lettuce” because the roots, which are packaged with the plant, are able to continue supplying the plant with moisture, allowing the leaves to remain fresh, crisp and flavorful for an amazing length of time. And growing hydroponic lettuce in a greenhouse is a very 'clean' method of growing lettuce. The chance of the lettuce being contaminated with something such as E-Coli (as has occurred in some organically grown crops) is extremely remote.

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Compared to field grown crops, hydroponic greenhouse lettuce is grown in a relatively pristine environment. Pathogens that may exist in the soil are of no concern since the plants are never in contact with soil. And growing in the method described produces some wonderfully sweet, crisp, and nutritious lettuce, which our customers sure do seem to appreciate!