What, No Soil?!

Hydroponics, in its simplest form, is growing plants by supplying all necessary nutrients in the plants' water supply rather than through the soil. The word derives from the Greek root words hydro and ponics, meaning water working. Growing plants hydroponically helps gardeners and farmers grow more food more rapidly in smaller areas (greenhouses, living rooms, classrooms, and rooftops, for instance) and to produce food in parts of the world where space, good soil, and/or water are limited.

When youngsters explore how to grow plants hydroponically (without soil), fruitful questions bloom: How can we provide support for plants without soil? How do plants grown with just water and nutrients compare with plants grown in soil? How can we get the tallest plants using a hydroponics setup? These types of questions can lead to active investigations and problem solving. Record-keeping becomes a natural outgrowth of these endeavors. Concepts related to basic plant parts and needs, nutrition, food production, recycling, agricultural technology and other areas come to life in these soilless growing environments. These studies may even lead to classroom business opportunities or fuel student career interests. Not the least of the benefits is the joy of students harvesting a crop of their own incredible edibles!

This guide features a synthesis of information from hydroponics experts and from people who have explored hydroponics with children in classrooms. It presents basic how-to information, suggestions for helping students discover concepts through investigations, plans for simple hydroponics setups, and stories from classrooms where students and teachers have investigated this growing technique.
Let the discoveries begin!

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PLANT NUTRITION PROBLEMS CAN BE SOLVED BY THE APPLICATION OF SCIENCE

Since perlite is devoid of available nutrients, the liquid feed applied to hydroponically grown plants is their only source of nutrition. This solution must therefore provide all the essential elements required for healthy growth and development. Moreover, each individual nutrient must be added at a rate which exactly matches its removal by the crop if deficiencies or toxicities are to be avoided. Thus, potassium may be added at a concentration of 400 mg/l, molybdenum at a mere 0.04 mg/l. Yet despite the 10,000-fold difference in concentration, molybdenum is just as important as potassium; without it there would be complete crop failure.

THE PERLITE CULTURE SYSTEM

When used for commercial crop production, perlite is contained in 20 to 30 liter perforated bags designed to hold three tomato plants. A constant supply of aerated nutrient solution is maintained in the perlite by sitting the bags in a shallow reservoir of solution formed in the bottom of an outer polyethene gully by a series of polystyrene dams. Perlite's strong capillary attraction for water automatically draws up water from the reservoirs at the same rate as it is lost by evapotranspiration, irrespective of weather conditions or stage of crop growth.

THE IDEAL ROOTING MEDIUM

Expanded perlite is physically stable and chemically inert. The porous nature of the cellular granules ensures a product that is light to handle, holds large quantities of readily available moisture and has a strong capillary attraction for water. Since it is free draining, it is also well aerated.

Its neutral pH, negligible nutrient content and a complete freedom from pests, pathogens and weed seeds combine to make this an ideal rooting medium for hydroponic culture.

WHAT IS PERLITE?

Perlite is a volcanic glass formed when larva cools very rapidly trapping small quantities (2-5%) w/w) of water. When the glass is crushed and heated to about 10000C, the trapped water vaporizes and puffs out the softened granules to form white mineral foam.

GROWING HYDROPONIC CROPS USING PERLITE

HYDROPONICS--- Hydroponic growing systems are based on a new generation of superb rooting media - inert, sterile, uniform materials such as the mineral perlite and rockwool. These products act merely as supports for a complete nutrient solution on which the plants depend entirely for their water, mineral nutrients and oxygen. In the purest form of hydroponics, there is a complete absence of solid substrate, the nutrient solution itself acting as the rooting medium.

Commercial growers can choose between three main hydroponic systems: one which uses a recirculating solution, the nutrient-film technique (NPT), and two 'static' systems, perlite culture and rockwool culture. The perlite culture system was uniquely devised and developed by a team of Scottish horticulturists. It is now the most widely used glasshouse crop production method in Scotland and it has the fastest growth of any hydroponic technique in the U.K. It is currently the subject of worldwide interest, particularly for use in arid zone regions.

FEEDING AND WATERING

Potting Soils as a Medium

Gardening with potting soils provides beginning growers with a simple, straightforward way to try out hydroponic gardening. Plants grow in nursery pots and can be watered by hand, eliminating the need for pumps, timers, and water systems.
Potting soils may look like garden dirt, but they are "soilless mixes", made with peat, vermiculite and perlite. Because these materials are acidic, potting soils also contain a very fine powdered dolomite lime to balance the PH of the mix. Since nursery pots restrict air and water movement, potting soils are a "chunky" texture to keep roots healthy.

These soilless mixes contain no fertilizer - you use hydroponic foods (dissolved in water) to supply plants with all the nutrients they need.


Here are some guidelines for gardening with potting soils:
1) Use a good-quality potting mix
Some "mixes" are pure peat moss! Your hydroponic supply store can recommend a good potting mix. Many growers use commercial growers' potting soils since they are top-quality mixes. For small (one to two gallon) nursery pots, use "Sunshine #1" Mix; for larger (three gallon or bigger) containers, try "Sunshine #4" mix - it's very chunky and won't pack down too much in the bigger pots.

2) Use hydroponic nutrients designed for soilless mixes.
Potting mixes "soak up" some of the fertilizer so manufacturers have developed precise foods for this method of gardening. They are inexpensive, easy to prepare, and your plants will love them! A good "green growth" fertilizer is "Peat-Lite" mix (20-19-18). The numbers refer to the amount of nitrogen, phosphorous and potassium in the fertilizer. These are minerals used in large quantities by plants, called the macro-nutrients. "Peat-Lite" also contains several other minerals, giving young plants everything they need for fast green growth.
Another potting soil fertilizer, for flowering and crop production, is called "Blossom Booster" (10-30-20). Note that flowering plants and plants in crop production use less nitrogen - the first number-but more phosphorous and potassium. The important thing to realize is that there are precise easy-to-use foods available for plants in potting soils for each stage of growth.

3) Use the right size nursery pot
Very small plants can start in a 4" or 6" pot. Soon they will need to be transplanted to a one gallon nursery container later. This is how to check if plants need a larger pot: Slide pot away from potting soil to check roots. (The pot will slide off easier if the soil is not soaking wet). If the roots are showing on the outside of the soil, and they are starting to wind around between the soil and the pot, it's time to move plants to a larger nursery pot. Plants that are kept in pots too long develop long, winding roots - they are called "root bound" or "pot-bound" plants, and they often dry out very quickly. Even when pot-bound plants are transplanted to larger containers, their winding roots are slow to spread into the new potting soil. Transplanting crops before they're pot-bound helps the roots to spread quickly into the new soil. If you see any of these signs in your garden:
- Plants dry out quickly between watering.
- Soil shrinks away from container, leaving an air space between soil and nursery pot.
- The soil surface collapses, forming a bowl shaped depression on the top of the soil.
- Surface soil forms a hard "crust". Water can't flow through this crust: it just runs off the top of the soil and over the side of the nursery pot.
Then it's repotting time! Here's a general guide for repotting for fast- growing plants: 4" to 6" round or square pots - repot after 2-3 weeks into 1 gallon pots. 1 gallon pots - repot after about 4 weeks into 2 or 3 gallon pots.
Remember, this is only a general estimate - your plants might grow faster or slower, so sliding off the nursery pot to check root growth is always the best way. Remember to moisten the new soil before re-potting, and water the plant well when you've finished to settle it into its new container.

4) Feeding and watering
- Never fertilize dry plants - water well first and feed 1/2 hour later to avoid "burning" roots.
- Always use room temperature water. (21*C=70*F)
- Feed your plants today, then use plain water the next time they are dry.
- Water well to moisten the entire root system, then allow pots to drain excess water.
- Let plants dry a bit between watering, so they're not waterlogged.
- If plants are wilting, you waited too long!

Why you should alternate watering and feeding:
When you feed your plants, some of the fertilizer is "sucked up" by the potting mix. If you fertilized every time, the nutrients would build up in the potting soil and damage your plant's roots. When you give your plants plain water between feedings, it re-dissolves the fertilizer in the potting soil, making it available to the roots and helping to avoid fertilizer build-up. Using the "feed-water-feed-water" method keeps roots healthy and satisfied while the top growth gets all the minerals it needs. Other hints":


- Keep nursery pots off cold concrete floors - cold roots mean very slow growth!
- If soil packs down, loosen it gently with an old kitchen fork.
- Plants in the same pot for more than 6 weeks may benefit from an addition of very fine dolomite lime - use one tablespoon dolomite for a one gallon pot, two tablespoons for a two gallon pot and so on.