Archive Article: March/April, 2006
Root vegetables are very easy to grow in hydroponics. Advantages to growing in hydroponics include outstanding quality and excellent flavor and nutrition. Most of the pests are soil born and no longer are a concern in hydroponics.
Because most root vegetables are relatively inexpensive, there has been little research on growing hydroponic root vegetables. However, NASA has been growing sweet potatoes in hydroponics as a possible food crop for space voyages. The sweet potato is the sixth largest food crop on earth, and has edible leaves
The George Washington Carver Agricultural Experiment Station at Tuskegee University has been growing sweet potatoes in hydroponics since 1986, and holds a patent for the process.
Scientists at Tuskegee recently developed a genetically altered sweet potato to increase the levels of protein in the tubers. While a person would require eight pounds of normal sweet potato to meet their daily protein needs, they would only require 3/5 of a pund of transgenic sweet potato to do the same. NASA has even developed a breakfast cereal using this high protein potato, but the gene altering process is highly controversial.
The sweet potatoes in NASA systems produce about one pound of sweet potato in six to seven days. Earlier experiments with hydroponic potatoes and carrots were producing one pound every four days.
Gericke’s potatoes
The first recorded hydroponic root experiments were completed by William Gericke in the early 1930s at University of California Davis.
Gericke’s first crops were in troughs dug into the ground, filled with a moss-like media and water supply below. The water supply had a 90 day supply of hydroponic nutrient, and at the end of 90 days, a large crop of potatoes was harvested.
Following Gericke’s basic concept, I built a garden of 10 plastic tubs, all Rubbermaid 10 gallon storage containers, and put a drain one inch from the bottom. Modifying Gericke’s method, I used perlite and filled the containers to about eight inches depth.
The very first root vegetables I tried to grow were radishes. The red globe table radish is one of the easiest of garden vegetables to grow, and usually can be grown from seed to radish in a single month.
But the radishes I grew on my normal hydroponic nutrient, a formula rich in nitrogen, did not grow into normal radishes. While the leaves of the radish were huge, very green and lush, the roots simply had a slight red thickening to a root system, no radish bulb at all. I tried a few crops and almost all the radishes were too small to be eaten.
The hydroponic nutrient I was using at the time had much more nitrogen than phosphorous. That is, its ratio of nitrogen to phosphorus was about 15/5 or three times more. The plants continued to put on green growth, and did not build up roots.
I started experimenting with a hydroponic root nutrient, one that has a relatively even amount of nitrogen to phosphorous and even more potassium, like 15/15/20. Basically the new nutrients increased the amount on mono potassium phosphate in the nutrient formula.
This restructured nutrient took about a year to perfect, and now grows wonderful radishes as well as other root vegetables. I have tried it with radishes, ginger, potatoes, sweet potatoes, carrots, turnips, onions, garlic, and other root and tuber vegetables. It grows a high quality root with very little effort.
Potato
The potato plant should be started with a seed potato, obtained from the local seed store. The potatoes in the supermarkets are often treated in some way to prevent sprouting, or in your case growing, and many have soil based diseases and rots that might appear in your crop.
Seed potatoes are grown in more sterile conditions to prevent diseases, and are small potatoes that have not been treated to prevent sprouting. The seed potatoes are of several varieties, with the red potato and the Yukon gold being two of the best for growing in hydroponics.
The instructions for planting potatoes in soil often say you can cut up a potato into many pieces and plant those. You only have to make sure that each piece has at least one eye, which is where the potato starts growing. However, this is often problematic and it is easier and more reliable to plant the entire small potato in the media. I use a fluffy perlite media, one that can be dug into under the plant.
The potato should be buried so that the top surface is an inch below the media. It should have about six to eight inches of media under the plant to give room for the roots to be in moist media. The drain hole or standing water should be about one inch of depth at the bottom of the media.
After the potato is first planted it should be watered from above with nutrient water every day, making sure any excess is draining from the container. The roots should start forming from the lower eyes and the shoots or green parts from the upper eyes. Green material should appear at the surface of the media in about a week. If two weeks go by and nothing forms, dig up the potatoes and look at them.
If the potatoes have not formed any roots and just rotted instead, the substrate was too wet, or the seed potatoes might not have been any good.
I grow the potato plants on a nitrogen rich grow nutrient until they reach full height, usually from 18 to 24 inches tall. A two square foot tub can have two plants in it. When they are full height, or starting to show the first blossoms, switch the plants to a root nutrient. Then small potatoes should start forming on the roots.
About two weeks after the first potatoes form, one potato should be ready to harvest. You have to feel around under the plant to find the largest potato. It may be that the potato stores all its energy in one potato, then the next. Anyway, that potato is ready to pick and eat.
According to Gericke’s information, a one pound potato can be harvested from each plant every four days. It you want two pounds of potatoes every day, you need about eight plants. The hydroponic potatoes are free from musty flavor and will probably be the best you have ever eaten.
Carrots
Carrots are grown in a softer media such as perlite or sand. The carrots that work best in hydroponics are the shorter ones. Any stubby carrot will work better than a long carrot because the media depth has to be about two inches taller than the length of the carrot.
Carrots cannot be transplanted so they have to be planted where they will be grown and harvested. If you try to grow the plants and then transplant, the resulting carrots are twisted and follow the path of the transplanted root.
A tub of eight inches in depth is adequate to grow carrots. The seeds should be planted about one inch apart so a square foot can grow 144 carrots. After they are planted they should start producing carrots in about 90 days. I start harvesting small carrots after about 60 days, thinning out the patch as they grow. It will continue to produce carrots for another 60 days.
If you want a supply of carrots every day you should have about six to eight square feet of carrots in production. Then plant two square feet every two months, and have three crops going. That should supply about half a pound of carrots every day.
Onions
Onions are actually bulbs, not really a root. The onion bulb usually grows half in the ground and half out. For hydroponics they can be grown in a relatively shallow growing bed of four inches in depth.
The easiest onions to grow are the string onions, small onions that are picked when less than ½ inch in diameter. Both the onion and the stems are used in cooking and in fresh salads and dishes. These grow in about six weeks from the time of starting seeds.
Onions are usually grown as seeds or they can be purchased as onions sets, usually a small container of at least 100 started onions. The spring onions have to be replanted about one inch apart. Larger onions such as Walla walla will grow much larger and have to be planted about three inches apart. That means a square foot of planting space can only contain about 60 onions.
The larger onions will be ready to harvest in about 90 days from seed and are then harvested as needed for the next 60 days. If the onions are getting too large or going to seed, they can be harvested and stored for use later
If you wish to have two medium sized onions every day, it will require at least four square feet of growing space.
Ginger
A ginger plant is one of the finest plants you will ever have in your hydroponic gardens. The plant itself looks like a delicate and graceful bamboo, and it smells of fresh ginger as it is brushed against. The root that grows below yields a bit of fresh ginger every day. A single plant will grow to a bush about two foot to three foot in height and about that in width. A two square foot tub will house only one ginger plant and it will produce only about an inch to two inches of fresh ginger root every day. This is not a productive plant, but the fresh ginger is a wonderful addition to a daily diet, and has important medicinal properties.
Ginger is being widely studied for its benefits for the digestive system. It is an important ingredient for many international dishes, especially Thai food and Indian traditional dishes. Most Indian dishes start with garlic, onion and ginger fried together.
Sweet potatoes
Sweet potatoes are started from small plants that sprout from a sweet potato. The way plants are usually started is to place sweet potatoes in a bed of sand, allow them a small amount of moisture. The springs should appear in a week or two.
Sweet potatoes bought from the store as vegetables may not sprout at all. They, like the potatoes, may have been treated to prevent sprouting. Seed sweet potatoes may be found in a nursery, or organic sweet potatoes from a farmers’ market may sprout.
The sweet potato is grown like the potato, but they’re slower to form.
Sweet potatoes are more nutritious than the white potato and are excellent in potato recipes as a substitute. They have a high vitamin C and vitamin A content.
Garlic
Garlic, for some strange reason, is fairly difficult to grow in hydroponics. The garlic grows slowly, both in ground and in hydroponics. It seems stubborn about increasing its growth rate as most plants do in hydroponics.
Garlic is grown from the cloves, each clove being planted underground, the pointed end up, and the top about one inch under the surface. The plants will start to sprout and grow after about a week.
After starting, the garlic takes a very long time to grow into a complete bulb. For a square foot the cloves should be placed every two inches apart. That means a square foot can have about 60 plants and they will take at least 120 days to produce full size bulbs, and sometimes 180 days. So to have a garlic plant every day you need four square feet. For just a few cloves you need less.
Fertilizers
Fertilizers are classified by the three numbers on the package which refers to the relative amounts of NPK, or nitrogen, phosphorous and potassium. In the USA, by law, the numbers are expressed as percentages by weight of nitrogen (N), phosphate (P2O5), and potash (K2O). A 100-pound bag of fertilizer labeled 5-5-5, there are 5 pounds of N, 5 pounds of P2O5, and 5 pounds of K2O. To convert P2O5 to actual phosphorous content, multiply the given weight by 0.43. To convert K2O to potassium content, multiply the given weight by 0.83.
Nitrogen fertilizers
Nitrogenous fertilizers (or urea) support the plant during the growth of leaves and foliage. The NPK ratio of nitrogenous fertilizers varies, but in India a ratio of 4:2:1 is considered to be optimum for food crops, especially rice and wheat (nitrogen is four parts, phosphorus in two parts and potassium in one).
Phosphourous fertilizers
Phosphatic fertilizers are also called fruit-and-flowering fertilizers since they aid the growth of flowers and fruits in plants. Ideally, the NPK ratio of phosphorous fertilizers is in the ratio of 2:3:2 (nitrogen is two parts, phosphorus in three and potassium in two).
Potassium fertilizers
Potassium fertilisers are root fertilizers since they stimulate the growth of roots of plants. Ideally, the NPK ratio of potassium fertilizers is in the ratio of 2:2:3 (nitrogen is two parts, phosphorous in two and potassium in three).
References
Hagan, H. 1995, Fertigation: An overview of some practical aspects Introduction
http://iclfertilizers.com/pdf/1-1.pdf
Hill et al. Utilization of sweet potatoes in controlled ecological life support systems (CELSS). G.W. Carver Agricultural Experiment Station, Tuskegee University, AL 36088, USA.
Imas, P., Recent Techniques in Fertigation of Horticultural Crops in Israel
c/o Dead Sea Works Ltd., POB 75 Beer Sheva 84100 Israel.
http://www.ipipotash.org/presentn/rtifohc.html
Kafkafi, U. SEVEN LECTURES ON SELECTED TOPICS, Sponsored by Haifa Chemicals Ltd
http://departments.agri.huji.ac.il/plantscience/topics_irrigation/uzifert/2ndmeet.htm
Mantag, Uzi, 1999, Fertigation in Isreal, www.fertilizer.org/ifa/publicat/PDF/1999_biblio_20.pdf
Waisel Y., A. Eshel and U. Kafkafi (eds.). 2002. PLANT ROOTS. THE HIDDEN HALF. Marcel Dekker, Inc. New York, Basel, 3. rd. edition.
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