Hydroponic Tomato Production

Hydroponic Tomato Production ©2013 Harley N. Smith All rights reserved. Nothing tastes better than a vine-ripened tomato, picked fresh from the garden...
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Hydroponic Tomato Production ©2013 Harley N. Smith All rights reserved. Nothing tastes better than a vine-ripened tomato, picked fresh from the garden in the middle of summer, thick sliced while still warm from the summer sun, drizzled with a little salt and olive oil, and served with a sprig of fresh basil. Why is it then that a supermarket tomato can be so tasteless, especially out of season? There are a variety of reasons. First, commercial growers are concerned mostly about yield, not about quality. They get paid to produce tons of big, red tomatoes that look good on the shelf; flavor is secondary. Second, modern, commercial tomato varieties are bred for size, color and resistance to common greenhouse diseases; again, flavor is secondary. Third, most commercial tomatoes are grown out of state or even out of this country. So to reduce damage during transport, the tomatoes are picked at “breaker stage”, barely yellow or pink, crated for cross-country shipping, then artificially ripened with ethylene gas to look better on the shelf; once again, flavor is secondary. It is possible, however, to produce delicious tomatoes year round, if flavor and quality are given first priority. With a properly managed hydroponic system, it is possible to double the lycopene content of tomatoes, increase vitamin-C content by up to 50%, and significantly improve the sugars, organic acids and flavors of tomatoes picked ripe from the vine. The grower may have to sacrifice a little yield, and he may have to limit distribution to a more localized market, but it is definitely possible to produce tomatoes that taste like they came out of the garden in August, year round! Indoor and Outdoor Production For the hobbyist, it is possible to grow a bumper crop of gourmet-quality tomatoes indoors under lights. For example, with a 3’ X 3’ flood-and-drain system under a 600watt high pressure sodium light it is possible to harvest literally thousands of vineripened cherry tomatoes all winter long. Flood-and-drain systems are great for medium sized plants. The plants are held in individual pots in the upper growing tray, and the water and nutrients are stored in a reservoir underneath. A timer clicks a pump on, flooding the roots with nutrient-rich water. When the timer turns off, the nutrient solution drains back into the reservoir, pulling fresh oxygen to the roots. For tomatoes, the timer is usually set to flood three or four times per day, and the lights are left on up to 16 hours per day. The trick is to choose a “determinate” variety of tomato such as Red Robin cherry tomatoes. Determinate varieties, sometimes designated as a “bush tomato” or “patio variety”, only grow to a certain height then stop. Little or no pruning or staking is required, and a bumper crop of ripe tomatoes can be harvested all winter long in a relatively small space. Outdoor hydroponics is a favorite of some tomato growers in the summer. For example, tomatoes can be started indoors under lights, transplanted into BATO buckets for early vegetative growth, and then spaced outdoors in rows for the summer. An irrigation line 1

is set up with individual emitters at each container, and inch-and-a-quarter PVC pipe is used to return the water and nutrients to the reservoir. To save space, the reservoir is usually buried or partially buried and the BATO buckets are placed at or slightly above ground level. In full sun, hydroponic tomatoes grow extremely fast, sometimes up to six inches per day, and yields are phenomenal. Best of all, there are no weeds to pull! The only down side to outdoor production is that the fruit must be protected from pests and animals, and summer storms can reek havoc on unprotected plants. But if a few precautions are taken, an outdoor hydroponic garden can be the envy of the neighborhood! Most commercial tomato production is done in greenhouses. Rows are oriented north to south so that plants receive the greatest amount of light, and indeterminate varieties are usually chosen. Unlike determinate varieties that reach a certain height and stop growing, indeterminate tomato vines continue to grow throughout the year, sometimes reaching lengths of more than 50 feet! Two wires are strung above each row, with rolls of twine called “tommyhooks” hanging down to the plants. As the vines grow, the plants are attached to the twine with vine clips, and any suckers are removed. Once the vine reaches the wire, a little twine is unrolled and the vine is lowered and slid down the wire. This method of vine training is called “lean and lower”, and the vines are wrapped round and round the rows as they grow. Indeterminate varieties allow a continuous harvest of tomatoes for the entire year. The tomatoes at the bottom of the vine ripen first. They are harvested, and the next set of tomatoes ripens. As the vine grows, the bottom leaves are stripped from the plant, the vine is leaned and lowered, and the top six feet of the plant continues to produce fruit and flowers. Since tomatoes are perennials, the process could continue for years, but after eleven or twelve months, the vines become so long that the transportation of water and nutrients becomes inefficient, and production begins to slow down. Therefore, most commercial growers replace the old vines with new vines after eleven months or so. Hydroponic Growing Mediums Several growing mediums are suitable for growing tomatoes in hydroponic systems. NFT systems use the least amount of growing medium. NFT, or Nutrient Film Technique, uses just enough growing medium to hold the seedling, and the roots grow directly in the flow of nutrient solution. Since tomatoes are long-term crops, the troughs must be wide enough to hold a massive root structure without clogging up the flow. If areas of stagnant water develop, anaerobic root rots can take hold and spread throughout the system. Therefore, NFT troughs at least 10”-12” wide are usually recommended for tomatoes, and care must be taken to ensure that all pumps are functioning properly. If a pump were to fail, a crop could be lost in a matter of hours! BATO buckets are sometimes used for greenhouse tomato production, either in recirculating or drain-to-waste systems. BATO buckets, also known as Dutch Pots, were designed in Holland as an improvement over standard plastic pots. Two tomato plants can be held in each BATO bucket, with two emitter stakes per bucket. Water and

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nutrients are pumped to each container through an irrigation line and returned to the reservoir through PVC pipes. Each BATO bucket is equipped with a specially-designed drainage elbow that creates a siphon effect for draining off excess water. If a pump were to fail, however, an inch or two of nutrient solution would collect in the bottom of the container, acting as a temporary reservoir for the plant. Most common growing mediums for BATO buckets are granulated rockwool, perlite, coconut fiber and expanded clay pellets. Sometimes a mixture of perlite/vermiculite is used, but vermiculite should never be used as the sole growing medium for tomatoes. Vermiculite tends to lock up important cations such as potassium, making them unavailable to the plant The most popular growing medium for tomatoes and other long-term crops is rockwool. Rockwool is made from basaltic rock, the material that the Earth’s crust is made of. The rock is crushed and melted at 3500 degrees F. The molten rock is then poured into spinning cylinders, similar to how cotton candy is made, and the rock fiber is spun and cut into blocks of various sizes and shapes. Sheets of one-inch rockwool starter cubes are made to fit into standard nursery trays, growing blocks of various sizes are used to hold individual plants, and slabs of rockwool are used to grow multiple plants in rows. Rockwool is an ideal growing medium since it has a perfect balance between air and water holding capacity. If rockwool is allowed to drain freely, it is nearly impossible to over water and kill young plants. Rockwool also has a “zero cation exchange”, meaning that none of the essential plant nutrients are “locked up” by the growing medium, so all of the minerals in the nutrient solution are available to the plant. Propagation In Rockwool Most tomatoes are started from seeds, and rockwool is an excellent propagation medium. A sheet of 98 one-inch starter cubes is placed in a standard nursery tray. Rockwool conditioning solution is then mixed and poured over the rockwool to soak over night. Rockwool conditioning solution has a pH of about 5.5 to neutralize the limestone dust retained in the rockwool during the manufacturing process. Once the pH is neutralized, the pH of the rockwool remains stable throughout its life. Rockwool conditioning solution also contains a mild nutrient solution to help seedlings get off to a good head start, and it often contains other beneficial ingredients such as B-vitamins and root promoters. The main purpose of the conditioning solution, however, is to stabilize pH, and pH adjusted water is often all that is necessary to prepare the rockwool for planting. When conditioning rockwool, make sure that the rockwool is completely submerged in conditioning solution, and allow it to soak for at least 24 hours. When you are ready to plant the seeds, drain off the excess solution so that the rockwool is not sitting in a puddle of standing water. If the rockwool is sitting in a puddle, the air pores can fill with water, and the emerging seedlings could suffer. So drain off all standing water then put a seed into each starter cube. Some growers like to cover the seeds with a layer of vermiculite or other water holding material, but if the rockwool remains moist, it usually isn’t necessary. It is beneficial, however, to cover the rockwool trays with a humidity dome, and to place them on a heating mat. The dome will retain the relative humidity at about

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98%, and the heating mat will hold the substrate temperature at about 78 degrees F., ideal for seed germination. While the seeds are germinating, leave the humidity dome on and place the tray under fluorescent lights, about 3 inches from the growing tips. Full spectrum fluorescents bulbs are best, since the red end of the spectrum helps stimulate root growth, but it is sometimes more economical to alternate full spectrum bulbs with cool white fluorescent bulbs for a germination station. The cool white bulbs are usually cheaper and they have plenty of blue spectrum light to help keep the emerging seedlings from stretching. Once all the seeds germinate, remove the humidity dome. If you leave the dome on too long, the high humidity can set up an environment for fungal growth that could eventually harm the seedlings. Just make sure that the rockwool remains moist. If the rockwool dries out completely, the tender seedlings will quickly die! To test for moisture, simply lift the tray a little to see how heavy it is. If needed, re-soak the rockwool with room temperature water and gently pour off the excess. Normally, however, the rockwool will retain enough moisture to last for at least a week or two. Once the first true leaves develop and the roots start to poke out of the bottom of the rockwool starter cubes, the tomatoes are ready for transplanting. Note that the “first true leaves” are not the first leaves that appear. The first leaves to appear are the cotyledons or embryonic leaves that emerge from the seed. They often die back once the plant starts to mature. The first “true” leaves are actually the second leaves that appear after the plant germinates and starts to grow, and their appearance is an indicator that new roots are developing. If in doubt, simply lift up a corner of the starter cubes and take a peak. If you see roots, the seedlings are ready to transplant! Since tomatoes are a long-term crop, it is often best to transplant the starter cube into a four-inch growing block as an intermediate step. As with the starter cubes, soak the rockwool blocks in pH adjusted conditioning solution 24 hours before transplanting. When ready to transplant, drain off the excess water then simply place the starter cube into the precut hole in the growing block. The plants can then go back under the fluorescent lights for a couple of more weeks until the roots start to poke out from the bottom of the growing blocks and the seedlings become better established. Rockwool-Based Hydroponic Systems Whether a hobbyist or commercial grower, rockwool-based hydroponic systems are an excellent choice for growing tomatoes and other long-term crops. Since rockwool has such a high air and water-holding capacity, large plants can be grown on a relatively small amount of growing medium without becoming root bound. For example, a one foot by three foot slab of rockwool, 2.5 inches deep, can support four full-grown tomato plants with 35 foot vines for a full year, and the same slab can be used to support another four plants the following year! Due to rockwool’s excellent drainage ability, it is practically impossible to over water and kill young plants, and due to its zero cation

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exchange capacity, it’s easy for growers to provide the perfect nutrient balance at the root zone. Once tomato seeds are germinated and the seedlings are established in growing blocks, the tomatoes can be transplanted to rows of growing slabs. Rockwool slabs are covered in plastic material to prevent unwanted algae growth. 24 hours before transplanting, the rockwool slabs are soaked in pH adjusted conditioning solution with the plastic intact. After soaking the slabs over night, drainage slits are cut into the plastic material and the solution is drained and discarded. The locations for each seedling is determined, Xshaped cuts are made in the plastic the size of the growing blocks. The cut portions of plastic is peeled back, and the growing blocks are placed on the exposed sections of the slabs, bare rockwool to bare rockwool. A drip emitter stake is then placed at each location to anchor each block and provide water and nutrients to each plant. It is best to push in the emitter stakes between the plastic and the rockwool, just below the surface a quarter inch or so. This will keep the surface of the growing block dryer, reducing algae growth. The grain of the rockwool is such that the roots grow vertically through the blocks and horizontally in the slabs. The nutrient flows over the roots, drains out of the slab, and is captured and returned to the reservoir. Rockwool is great for recirculating systems. Enough nutrient solution can be provided at each irrigation cycle that 35% or more leachate can be recovered without over watering the plants. The more leachate, the closer the EC in the slab is to the EC in the reservoir. At the hobbyist level, tomatoes can be irrigated 24 hours per day without adverse effects. But at the professional level in a greenhouse, the irrigation cycles are more precisely timed to help steer the crop and help prevent fruit disorders such as cracking and russeting. Shorter irrigation cycles more times per day tend to steer the crop in the vegetative direction (more vines and leaves). And longer irrigation cycles fewer times per day tend to steer the crop in the generative direction (more fruit and flowers). Also, since plants don’t take up as much water at night, stopping all irrigation before nightfall tends to better drain the slab and prevent excessive root pressure. Hence, fruit cracking and other cultural problems associated with unbalanced irrigation can be reduced or eliminated all together. Generally speaking, irrigation cycles in a greenhouse are determined by light levels. In a modern computer-controlled greenhouse, light sensors are used to measure accumulated light levels every ten minutes. No irrigation is required until the plants become photosynthetically active, normally about 2 hours after sunrise. Once the plants accumulate about 250 mega Joules of light energy, the first irrigation cycle is triggered, and additional irrigation cycles are triggered during the day, driven by the amount of accumulated sunshine. On overcast days, when light accumulates much more slowly, a timer overrides the system so that the rockwool doesn’t get too dry between irrigation cycles. The computer also factors in other variables such as temperature, humidity, stage of plant growth, and nutrient concentration to fine tune irrigation rates for optimal yields.

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Nutrient Solution Management Hydroponics allows precise control of plant nutrition at the root zone. In other words, hydroponics is like creating the perfect soil. Or more precisely, hydroponics is like creating the perfect soil for each stage of the plant’s growing cycle. At the vegetative growth stage of tomatoes, a grow formula can be used that is proportionally higher in nitrogen. At the fruiting and flowering stage, a bloom formula can be used with increased levels of phosphorous and potassium. During the maintenance stage, when all the vines are bearing heavily, a boost formula can be used to help maintain the proper nitrogen to potassium levels between reservoir changes. During heavy fruiting and flowering, all of the potassium can be removed from the reservoir in a matter of days. If the plants suffer from potassium deficiency, the fruit will be watery with low sugar content and poor shelf life. Therefore, using a boost formula will put back into the reservoir what the plants took out. If, on the other hand, too much potassium is added to the reservoir, potassium toxicity can occur. Potassium toxicity shows up as a magnesium deficiency, so the bottom leaves will start turning yellow. If this happens, simply back off on the boost formula. In severe cases, spraying a mild solution of Epsom salts (magnesium sulfate) on the lower leaves will green the leaves up over night. EC is also important to vigorous plant growth and good fruit quality. During the vegetative growth stage, a low to medium EC is recommended: somewhere between 12 and 24 cf. At the fruiting and flowering stage, medium to high EC is recommended; somewhere between 24 and 38 cf. Experienced commercial growers can go even higher, up to 60 cf! There is a direct proportional relationship between the EC levels and sugar content in the fruit. Although high EC’s tend to restrict vegetative growth, resulting in a little less overall yield, increased sugar content makes the tomatoes taste more like homegrown from the garden! There is also a direct proportional relationship between EC and lycopene content. Lycopene is the red pigment in tomatoes, and it is a powerful cancer-fighting antioxidant. According to studies done at the University of Arizona, tomatoes grown at very high EC’s (40 to 50 cf) can result in doubling the lycopene content of the fruit. Raising the EC at the root zone creates a salt stress, making it harder for the plant to take up water. Under stress, the plant condenses sugars, vitamins, organic acids and antioxidants in the fruit to protect itself and store up energy for reproduction. For example, vitamin-C production can rise by as much as 50% when the plants are subjected to just the right levels of EC stress. Don’t overdo it, though. Every plant has its limits, and if you push the plant too far you can hurt the plant more than help it. If, for example, you raise the EC under hot, dry conditions, the plant might not be able to take up enough water fast enough, and it will begin to wither, turn brown and die! If you see signs of stress, such as leaf curling, that’s still all right, but if you see signs of “burning” at the edges of the leaves, add more water

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to lower the EC and reduce the stress on the plant. Experience will show you just how far you can push your tomatoes, but remember that every cultivar is different! pH is also important to healthy plant growth and good fruit quality. Most plants do well at a slightly acidic pH of 5.8 to 6.4. Tomatoes tend to fall into the acid-loving category, with a pH of 5.8 to 6.0 being a good target. Some growers will go as low as 5.5 with no apparent negative side effects, especially when growing in rockwool. The addition of small amounts of organic biostimulants to the nutrient solution can also improve quality and yield. For example, amino-acid blends can result in earlier ripening and extending shelf life. Glutamic acid and glycine improve the calcium pectate levels in the skin of the fruit, and methionine is a precursor for natural ethylene production, triggering and enhancing the ripening process. Seaweed extracts, B-vitamins, and humic acid can stimulate the production of enzymes that protect the plant under stress, and bloom stimulants can introduce zinc-finger transcription factors to increase flower and fruit production at the genetic level. If plants can be conditioned to handle increased levels of stress, it may be possible to push EC levels to new heights without harming the plant! Horticultural Lighting Tomatoes are light-loving plants and do best in full sunshine. So for indoor gardening, light is the limiting factor for strong plant growth. Tomatoes, like most other plants, need full-spectrum light to grow and reproduce. During the vegetative growth stage, tomatoes prefer the blue end of the spectrum, and during fruiting and flowering, tomatoes prefer the red end of the spectrum. During the vegetative growth stage, metal halide lighting is the lamp of choice. Metal halide lights are full-spectrum lights, rich in the blue end of the spectrum. Blue is responsible for chlorophyll production more than any other color in the spectrum, and blue at the 460 nm wavelength is the only wavelength that influences phototropism (leaning towards the light). If you bomb a tomato seedling with plenty of blue spectrum light, the plants will be short and stocky, with thick stems and plenty of dark green foliage. On closer inspection, the leaves will have thicker cuticle cells (waxy covering) to help protect them against fungi and disease, and the stomata, the pores used to take in carbon dioxide, will be more numerous and denser on the undersides of the leaves. In short, the seedling will turn into a vigorous, photosynthesis machine, revved up to produce a bumper crop of future fruit! A 400 watt MH lamp will cover up to a 4’ X 4” area. So it is important to keep the light as close to the plants as possible without burning the leaves, usually about a foot to a foot and a half above the growing tips. It is best to hang the light on chains with S hooks, so that you can easily raise the lights as the plants grow. An alternative to metal halide lamps are the new T-5 high output fluorescent lamps. An eight-bulb fixture puts out over 400 watts of light energy, but much less heat than MH bulbs. Therefore, it is possible to place the lights much closer to the seedlings without burning them. If space is at a

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premium, the T-5 fixtures can be easily mounted on shelves, allowing a much better use of vertical space. Side by side trials between MH and T-5 lights show comparable results for vegetative growth of tomatoes, but T-5 lighting is more energy efficient. At the fruiting and flowering stage, plants prefer the red end of the spectrum, and high pressure sodium (HPS) lamps are the lamps of choice. A good horticultural HPS bulb is rich in the red and far red portions of the spectrum, stimulating fruiting and flowering, but it has just enough blue spectrum to help prevent the plants from stretching. Standard HPS bulbs, such as those used in warehouses, are not recommended for indoor growing. Standard bulbs have almost no blue light, and plants grown under them will tend to be tall and spindly with poor yield. So when growing indoors under all artificial light, make sure that the HPS bulb is rated for horticultural use. A 1000 watt HPS light will cover up to a 6’ X 6’ area when no other light source is available. In a greenhouse setting, a 1000 watt HPS lamp will cover up to a 10’ X 10’ area. HPS lamps are the norm in greenhouse tomato production because there is usually plenty of blue light available from the sky to keep the plants from stretching. The HPS lamps are used only to extend the day length and stimulate increased fruiting and flowering. For the best results when growing tomatoes indoors, germinate seeds under fluorescents, grow seedlings under MH or T-5 lighting, and produce fruit under more powerful HPS lamps. The MH light will provide strong, vigorous plants and the HPS light will provide a bumper crop of fruit and flowers. Don’t skimp on light! Temperature and Humidity Control Since tomatoes are native to tropical climates, tomato plants can thrive at relatively high daytime temperatures of 75 to 80 degrees F, with night time temperatures between 65 and 70 degrees. In a computer controlled greenhouse, night temperatures are determined by accumulated light measurements. The computer measures the total accumulated light during the day, and adjusts the night time temperatures accordingly. If the previous day had a high level of accumulated sunlight, the night temperatures are raised to increase the metabolism of the plants. But if the previous day was cold and overcast, energy can be saved by lowering the night time temperatures without sacrificing yields. Temperature control can also affect the size of fruit. If larger tomatoes are desired, night temperatures must reach target levels as quickly as possible. As dusk approaches, the computer senses the decreasing light levels and rapidly lowers the greenhouse temperatures to the night time levels. Since the leaves cool down faster than the fruit temperature, most of the water and photosynthates are transported into the warmer fruit, and the fruit swells to a larger size! Humidity control is also important for fruit quality. Under high humidity, less water vapor is transpired from the plant. The transpiration stream is very important for calcium uptake, so under high relative humidity a calcium deficiency can easily occur. Calcium deficiency shows up as blossom end rot in the fruit, making the tomatoes unsaleable! To a hobbyist, a simple thermostat/humidistat controller is usually enough to keep

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temperature and humidity at acceptable levels, but commercial growers need a greater level of control. In an advanced computer controlled greenhouse, the computer measures air temperature, tissue temperature and relative humidity to determine the vapor pressure deficit (VPD) of the plants. Low humidity (high VPD) can be as detrimental as high humidity (low VPD). If the VPD is too high, the leaves will transpire too rapidly, and not enough calcium will make it into the fruit. If the VPD is too low, the leaves won’t transpire enough and not enough calcium will make it into the fruit. Either extreme could result in blossom end rot! Computer controls that factor in VPD pay for themselves very quickly in a commercial greenhouse. They not only prevent blossom end rot more effectively, but they are more energy friendly than conventional humidity controls and thermostats. Driven by VPD calculations, computer controls actuate exhaust fans, heating and cooling systems in incremental stages to keep the transpiration stream active at the lowest possible energy costs. Indoors, ideal temperatures and humidity are easy to maintain since the ambient atmosphere is usually at a comfortable “room temperature” of 68 to 72 degrees F. When the lights are on, the temperature is naturally a few degrees higher than when the lights are off at night, ideal for growing good tomatoes. In fact, if the growing area is in a large enough room, a simple oscillating fan is often more than adequate for keeping temperature and relative humidity at acceptable levels! Even the light bill is relatively insignificant for a small indoor tomato garden, usually less than $1.75 per day. So if you love gardening, and you are on a quest for the perfect tomato, then a modest indoor hydroponic garden may be just right for you. In a commercial greenhouse, temperature and humidity control is not as easy, and overhead can quickly erode profits! Greenhouses have a low R-factor. In other words, they do not have very good insulating ability. Most greenhouses have to be heated in the winter and cooled in the summer, and they can be very energy inefficient. Computer controls can help increase efficiency, but even computers have their limitations. Therefore, it is not uncommon for commercial growers in northern climates to shut down their greenhouses during the coldest winter months to save on the high costs of heating. Other growers choose to operate at a loss in the winter in order to retain market share. Not a good option! As fuel costs and electrical costs continue to escalate, new, improved insulating materials for grow rooms and greenhouses must be developed, especially for growing tropical crops such as tomatoes. For example, Blue Max insulated concrete has an R-factor of 50, compared to an R-factor of 15 for a typical greenhouse. With adequate insulation, horticultural lighting can do double-duty, providing both heat and light in the cold winter months. Other energy-saving technologies are also on the horizon. For example, hybrid lighting systems, combining fiber optics with high efficiency l.e.d.’s, can efficiently harvest wind and solar energy and produce low-cost lighting for underground grow rooms. By developing other emerging technologies such as alternative energy production, co-generation of heat and electricity, computer environmental controls, and modern hydroponics technologies, winter production of tomatoes and other tropical crops will become more economically viable in northern climates.

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