Introduction to Hydroponics
The term hydroponics means growing crops without soil. In soil, plants draw nutrients from the ground; in hydroponics, roots sit in a complete liquid fertilizer that supplies every essential nutrient.
Some systems anchor plants in a soilless medium such as rockwool, coconut fiber (coir) or clay pellets. Others use no solid medium at all, and roots hang directly in the solution. Either way, plants get their nutrients from the solution rather than from soil.
Most hydroponic systems are under cover, usually in greenhouses, for the most control over growing conditions. Without soil to absorb and buffer it, rain falling into an open system would change the solution's conductivity and upset its balance. Most outdoor systems are found in dry climates.
Hydroponics can go almost anywhere, including vacant lots, rooftops and places with poor soil or limited water. Systems range from hundreds of acres down to a windowsill, and can be stacked vertically. Skipping soil also lets growers sidestep weeds, soilborne diseases and soil fertility problems.
Types of Hydroponics Systems
Whether bought or homemade, hydroponic setups come in many configurations, but most food-growing systems fall into two groups: those that use a solid medium in place of soil ( substrate systems) and those that don't ( liquid systems).
In any system, seeds are usually sown in soilless plugs or mats that hold the plant for its whole life. Long-season fruiting crops are typically started in small plugs that are later set into a larger block, often a 4" (10 cm) cube, so seedlings can size up before going into the production greenhouse.
Quick crops such as lettuce and greens usually go into the system in their original plug without moving up to a block. Plugs, blocks and mats are most often made of coir, rockwool or inert foam such as Oasis cubes.
Substrate-Free / Liquid Hydro Systems (No Solid Medium)
In liquid systems, roots sit directly in the nutrient solution with no solid medium holding the plants. They can be designed many ways, but there are three basic types:
-
Nutrient film technique (NFT)
One of the most widely used systems, NFT grows plants in long gutters or channels, usually with a cover on top that has holes for the plants. Roots grow in the channel with nothing but a small plug holding each plant. Solution is pumped in at the high end, runs down the channel and drains out the low end; the "film" is the thin stream of solution flowing past the roots. Many growers also add an air pump and air stone (a porous stone that releases fine bubbles) to boost oxygen in the solution.
-
Deep-water culture (DWC)
In deep-water culture, roots hang in a reservoir of standing nutrient solution. Plants grow in tubs or basins rather than channels, usually held in floating rafts with nothing but plugs to support them. Since the roots are fully underwater, they need added oxygen, usually from an air pump and air stone in the reservoir.
A hydroponic butterhead (Boston) lettuce. In NFT, roots grow in the channel held only by a small plug.
-
Aeroponics
Aeroponic designs vary a lot, but all of them hold plants with roots suspended in air and spray them with a fine nutrient mist at set intervals. The big advantages are more oxygen for the roots and a much lighter system.
Pea shoots in a modified NFT system at Olivia's Garden, New Gloucester, Maine. Photo © Olivia's Garden.
Solid Medium / Substrate Systems
Systems that use a medium fall broadly into container culture and slab culture. The medium can be almost anything, including burlap, rockwool, coir, hemp, sand, perlite, sawdust or wood chips.
Hydroponic tomatoes grown in containers at Olivia's Garden, New Gloucester, Maine. Photo © Olivia's Garden.
-
Container Culture
In container culture, plants grow in containers filled with a soilless medium. These can be purpose-made buckets, pots or grow bags, or repurposed bags, buckets and the like. -
Slab Culture
In slab culture, plants grow in long, flat slabs of medium made for the purpose, commonly rockwool, hemp, burlap or coco coir. Sizes depend on the crop and conditions, from quite thin up to a couple of inches deep, roughly a foot wide and a few feet long. Several plants grow from the top of each slab, the number depending on the crop. Slabs, particularly for big plants, are wrapped in plastic or biodegradable film to hold in the solution, and are lined up end to end to make a row.
A key difference between the two groups: substrate systems usually need an emitter for each container or slab to deliver solution to the roots, while in liquid systems the channel or basin keeps the solution around the roots.
Aquaponics
Aquaculture Centre of Excellence, Lethbridge College, Alberta, Canada
Aquaponics grows crops using the nutrient-rich wastewater from raising fish or other aquatic animals, making an efficient combined food system. It can be paired with any of the hydroponic systems above.
System Choice
In principle, almost any crop can grow in any system. In practice, media-based systems such as slabs or buckets are favored for fruiting crops like tomatoes, cucumbers, peppers and eggplant, while liquid systems are favored for lettuce, greens and herbs. Microgreens and shoots are often grown in modified NFT channels lined with burlap, hemp or a similar material to hold the roots.
The Growing Differences: Hydro vs. Soil
Attentive Management
Like any engineered system, hydroponics works only as well as it's designed and run. Some field crops can go a long time with little care, but hydroponic systems need daily management. Plants aren't "watered" so much as fed water and nutrients through a solution delivered continuously or on demand by a circulating system. Because they have smaller root zones and none of soil's buffering, hydroponic crops suffer faster and more severely when a pump or timer fails or the solution gets out of balance.
Fertility Programs
Fertility needs also vary a great deal with the crop, the growing environment, the region and the season, and success depends on a nutrient solution that fits all of these. Beginners should start with a complete, manufacturer-designed nutrient program suited to their situation. Once they know how crops should look and perform, experienced growers can mix custom blends from individual fertilizer salts.
Popular Crops
The food crops most often grown hydroponically are tomatoes, lettuce, cucumbers, greens, peppers, eggplant, strawberries, herbs, microgreens, and shoots. They fall into two production models: short-cycle and long-cycle.
- Short-Cycle Crops such as lettuce, greens, herbs and microgreens mature fast and yield heavily over a season because they're planted and harvested again and again, as many times as conditions allow. Switching varieties with the seasons can help keep production going year-round.
- Long-Cycle Crops are the fruiting crops: tomatoes, cucumbers, peppers and eggplant. Depending on location, they're usually grown in two cycles a year (a short summer crop followed by a longer winter crop) or in several staggered plantings to stretch the harvest.
Living Harvests of Herbs & Microgreens
These Basil plants grown hydroponically and sold as a living harvest. Photo courtesy of a retired seed sales representative.
Hydroponics is a natural fit for selling a "living harvest." Plants come out of the system quickly and cleanly with roots attached, so growers can harvest by simply lifting them out and selling them whole.
The big plus is longer shelf life, since the moist roots keep the plant going.
Live plants work well for delicate crops like culinary herbs and microgreens. Live basil is usually sold potted in a protective sleeve, and live microgreens may be sold in clamshells with the medium still attached.
