The greenhouse is a familiar structure, found worldwide in a vast array of styles and designs that vary from place to place. This issue I’ll discuss the greenhouse and all the qualities that make it ideal for cultivating virtually any plant species.

I’ll also present an interview with Jeremy Marsh, who owns and operates H2Organic Farms, a 14,000 square foot state-of-the-art greenhouse that currently produces some of the most desired varietals of heirloom tomatoes in the Denver Metro area. He’ll take us on a brief tour of his operation and talk about his interest in gardening and producing high-quality produce.

Why Grow in a Greenhouse?

Many different factors go into having a productive greenhouse. Positioning and direction are very important if you plan on erecting a new house from the ground up; things like latitude and the kinds of plants you wish to grow will figure into finding the best way to position your greenhouse.

I’ve heard that a greenhouse positioned north and south in an area that receives full exposure all day will provide the most uniform delivery of sunlight for superior crop performance, but ultimately factors such as crop and time of year will also affect this decision.

Ventilation and insulation are both important control qualities in a properly built greenhouse. During the warm season excess heat is controlled through fans, retractable panels and shade cloth. When winter weather arrives, you’ll need adequate insulation to deal with cool nighttime temperatures that might discourage optimal growth.

Standard protocol to combat freezing temperatures for days or even weeks at a time might also entail natural gas heating. Although this method is extremely costly and somewhat inefficient, it is effective for supplemental heating purposes.

Greener techniques and systems exist as well; one I’ve seen recently uses heat recycled from incoming light entering the greenhouse, which is then captured at the highest point in the house, transferred to a water source and projected through plumbing. The heated water is then used to warm the ground and maintain a stable and consistent temperature in the greenhouse even during the coldest parts of the year.

Used in conjunction with sunlight, supplemental lighting might allow greenhouse growers to meet the micromole—or radiant light energy—levels required in order to achieve specific crop growth. Greenhouse lighting set-ups are becoming more prevalent as the year-round gardening market increases in popularity—you’ll find a variety of styles, types and technologies on the market, all engineered to increase crop performance in greenhouse situations. New products include double-ended 1,000 watt HPS fixtures that utilize innovative Dutch 400 volt lamp technology.

Unlike indoor gardening with horticultural lighting, greenhouses are not necessarily the best places to use air-cooled reflector housings that extract heat out of the house. Several theories exist to support this reasoning. First, air-cooled reflectors tend to be large, heavy and expensive—and a larger reflector will result in a larger shade spot. In fact, a larger reflector might ultimately deflect just as much natural light penetration as the supplemental artificial light the fixture helps provide.

Light is also lost through the duct ports on air-cooled reflectors, while their non-air-cooled counterparts reflect this light back down to the canopy. Ideally you should implement a reflector design that disperses light in a broad and uniform pattern instead of a direct penetration design that promotes a specific footprint. In the greenhouse your HID lighting is working in conjunction with sunlight, so typically a light will cover a much larger area than it would if you were growing indoors solely under artificial light.

Drip irrigation is commonly used in greenhouse growing for larger, long-season crops. Drip systems are extremely efficient in terms of water conservation and delivery—pressure-compensated emitters that allow only a specific amount of water to reach the planting site increase uniform productivity with minimal waste from run-off water.

Drip systems are very versatile in accessing harder-to-reach areas and are easy to assemble and relatively inexpensive in comparison to other automated systems. NFT (nutrient film technique) systems are also very common in greenhouses that are producing leafy, short-season crops such as herbs and lettuces.

These systems are comprised of rain-style gutters connected together lengthwise—a submersible pump delivers a nutrient solution to each gutter, creating a small stream of water running through the bottom of each channel. Although completely hydroponic, these systems are also relatively cheap to assemble, since there is virtually no grow medium required aside from whatever was used to sprout the initial seed or cutting.

Another form of greenhouse agriculture, which combines fish farming with plant propagation, is aquaponics. This form of hydroponics utilizes fish tank water, using fish waste to supply the plants with the beneficial elements they require for growth. These systems can be a little trickier to operate as there are two different elements involved—plants and fish—each requiring individual care.

In my interview with greenhouse grower Jeremy Marsh, I ask him to share a few of his personal techniques with our readers and let us in on the secrets that have allowed him to become a successful large-scale heirloom tomato producer.

Lee McCall: When were you first introduced to greenhouse growing?

Jeremy Marsh: I first started greenhouse growing in February 2011 after many years of bountiful backyard gardens. I've been growing on a commercial scale for over a year now.

Lee McCall: How many tomatoes are you harvesting at any given time?

Jeremy Marsh: Last summer I harvested ripe tomatoes to order, picking roughly 250 pounds a day about four to five times a week. Currently, I have three times as many plants—approximately 2,600—each expected to yield about a pound a week.

Lee McCall: What style of growing are you using?

Jeremy Marsh: I'm currently growing with a drip system, using coco coir in plastic five gallon grow bags. I plant two plants per bag with one dripper per bag. This is a basic hydroponic system that allows me to use organic inputs throughout the cycle. Nutrients are fed to the plant with each watering cycle and I also add several amendments to the coco to help get the plants off to a strong start. I strive to produce the best-tasting tomato I can by using products to increase the brix level in the plant…the higher the brix, the better the flavor, due to a healthier plant.

Lee McCall: What are the most productive times of the year for you?

Jeremy Marsh: The most productive season for me is late spring because of the additional hours of sunlight, an increase in the sun's intensity and the young age of the plant starts.

Lee McCall: How early in the year will you sow seeds in preparation for spring planting?

Jeremy Marsh: Field crops are planted out in late May to June. Seeds are planted in preparation beginning in February or March, depending on the variety and size you want. For the greenhouse crop the plants are seeded in early winter and produce through the following December—you get about 10 months of production with a successful tomato crop inside a greenhouse.

Lee McCall: What’s the largest fruit you’ve ever grown?

Jeremy Marsh: Last summer I grew a giant pumpkin that weighed 427 pounds. The giant pumpkin plant sprawled about 30 feet in every direction and it was lot of fun to watch it grow! I hope to someday break the 1,000 pound mark with a giant pumpkin.

Lee McCall: What is your preferred style of indoor gardening?

Jeremy Marsh: I like the drip system that I'm using for automated irrigation and the coco has been a great medium overall. Coco coir has many benefits over other mediums, in my opinion. It’s easy to flush if needed and is fairly cost effective. It holds up better than peat, which is good for a long crop like tomatoes. Coco also absorbs water readily and keeps well aerated. The cloth aeration containers also work really well and can be implemented in many types of systems, including ebb and flow systems. I've found these to work well and they are easy to use. The increase of oxygen to the root zone, as well as the root pruning caused by these containers, tends to improve plant growth rates.

Lee McCall: Do you have any nutrient preferences?

Jeremy Marsh: Plenty of Mycorrhizae—Glomus intraradices in particular—and cold pressed kelps and fish emulsions are a definite plus as they increase vitality and color. Supplemental calcium is also a must for tomatoes to prevent blossom end rot and promote healthy structure. Go organic if possible.

Lee McCall: What’s the best advice you have for someone growing tomatoes?

Jeremy Marsh: Tomatoes like a lot of food throughout their life cycle so choose a plot with rich soil and amend the plot based on a soil test. A drip system is the best way to water as it doesn't disturb the root zone and it also doesn't get any water on the foliage, which can create problems.

A drip system will enable you to consistently water your tomato plants with ease, allowing you to focus on pruning and training your plants rather than watering. Also, the early morning (at sunrise) is the best time to water your plants and also the best time to pick your produce for the longest shelf life and best flavor. Keep a close eye on your plants and research any issues that may arise quickly, to avoid major problems.

Lee McCall: What’s the most common problem you encounter in the greenhouse?

Jeremy Marsh: Keeping the conditions ideal and consistent throughout the greenhouse is a challenge. Maintaining temperatures can be difficult on the hottest days in the summer and the coldest nights during the winter, depending on the type of greenhouse you're using. There are many things that need to be continuously monitored and adjusted to maintain ideal conditions. Thrip screens on the air intake, predator insects and constant monitoring are all required to avoid catastrophic problems.

Constant sanitation practices are required to avoid diseases—there's always the threat of a virus taking over and wiping out the entire crop. Pests not only damage your crop but can also spread diseases, which could kill the entire crop. There is also the major challenge of keeping the plants supplied with the correct levels of macro and micronutrient, which can be monitored through regular tissue analysis as well as visual monitoring.

Lee McCall: What are your favorite varieties to grow?

Jeremy Marsh: I have grown several heirloom varieties with varied results—my favorite heirloom so far is the Aunt Ruby's German Green, which is a green tomato with an amazing flavor. I have many varieties, colors and flavors of heirloom tomatoes. My favorite hybrid is the Big Beef, which has a good flavor with a high yield potential.

I also have many varieties of greenhouse-specific tomatoes that produce much higher yields than the heirlooms, but the flavor of some of the heirlooms is hard to match. I also grow some of the world’s hottest peppers—like the ghost pepper (bhut jolokia) and the Butch T Scorpion pepper.