Hydroponic Systems for Water Gardens

hydroponic chives

A flood-and-drain table grows chives in rockwool blocks. These tables can be stacked and placed on wheels for restaurants to have ready access to fresh herbs and microgreens.

A career in water has introduced me to many different industries. I am fortunate to have been involved in several of them over time — water features, natural lakes and ponds, and even wastewater — with water flow, filtration and aeration equipment the common factors.

Working with water features led me to aquatic plants, and eventually, with the help of some friends in the industry, I opened my own aquatic plant nursery. We used plants to filter water gardens, became involved with recirculating aquaculture and raised fish at high densities. This industry introduced me to aquaponics — the process of growing fruits and vegetables using fish waste.

As I become better established and more experienced in the hydroponics industry, I would encourage my creative, innovative friends in the water feature industry to consider looking into hydroponics for a home garden, a larger project or simply your own curiosity.

Aquatic Engineering 101

Workers harvest lettuce after lifting a raft out of a DWC raft system.

Hydroponics is the culture of plants without soil. The plants have all the available nutrients they need in a water-based nutrient solution that is delivered to them through a carefully designed system. They are cultured in designated contained spots and, if needed, supported vertically with trellising. Note that these plants do not grow structural roots in these systems; they grow almost entirely feeder roots. This saves energy that can be redirected into vegetative and fruiting growth. The result is a recipe of formulated nutrients constantly being delivered to them in a biologically available form. These formulations are generally well researched and designed both for the plant species and the stage of growth of that particular plant.

The plants are easy to culture because there are no weeds. They are cleaner after harvest. With well designed, complete nutrition, they are generally resistant to pests.

Did I mention there are no weeds?

How Does it Work?

A reservoir is required for supplying water to the plants. Make sure it’s not too small, since you will be fine-tuning the water chemistry and will need fairly good buffering against high temperatures. As we all know, you must keep it covered, or it will grow our old friend — algae.

Aerate the water with an air stone. This adds oxygen, which the plant roots enjoy, and keeps nutrients uniformly mixed. A magnetic-drive pump can be used for circulation. Black vinyl tubing or PVC will deliver the water to the plants. (This should all sound really familiar.)

Next, decide which plant or plants to grow and find the conditions they desire. The parameters you should be concerned with are pH (generally lower than fish or biofilters enjoy), electrical conductivity (EC), temperature and oxygen levels. Choose plants with similar preferences or create separate systems for each. If you don’t, you will be tasked with splitting the difference with the water chemistry to make them all happy, likely compromising your results.

EC results from dissolving nutrient salts in the water. A testing pen is available to monitor both pH and EC. For simplicity, buy a commercially available fertilizer mix. There are many. Don’t get analysis paralysis due to marketing claims and fancy labels. Do basic research and purchase based on your crop. Purchase and have on hand pH products to achieve and maintain a healthy pH throughout your grow.

After you have a reservoir of aerated, mixed nutrient solution formulated to make your specific crop happy, you can stand back and watch the magic. The magic happens at the roots. Unlike most other gardening and farming, you can observe the progress directly. When the roots develop, the vegetative growth follows. You will be impressed as the roots develop and enjoy the nutrients that are so effortlessly available. Many of us have seen this with plants in water garden streams, and the robust growth with hydroponics is similar.

Grow Systems

bok choy aquaponics

Bok choy seedlings thrive in this NFT system.

And now, the fun part — choosing your plant system. You have probably seen or heard of some of the approaches to aquaponics. Here I’ll introduce five popular types of systems.

Nutrient Film Technology (NFT) provides water with a slow delivery in a gutter-type system. The gutter has a cap over it with holes cut at intervals. The water in the gutter runs down small ribs on the bottom in a thin layer — a “film” of nutrient solution constantly being delivered to plant roots. A small net cup with a small seedling in substrate is placed in each of the holes. This can be duplicated as a DIY project with PVC pipe and a hole saw, with designs and instructions readily available online. This system is typically used to grow leafy greens.

Dutch buckets are another option. These have specially designed drains for adapting to a central PVC pipe drainage trunk. Just fill the bucket with an inert substrate, such as coco fiber, perlite or a mixture. Many substrate mixtures are available by the bag. They will differ in their ability to hold water and nutrients, as well as porosity, which will allow oxygen to reach the roots between feedings. The buckets are lined with a mesh. I use paint strainers, which are inexpensive and readily available, to prevent any substrate from returning to the reservoir. The bottom drain assembly has an ell that pulls out all nutrient solution after a feeding, and the bucket adapts to fit over a 1 ½-inch PVC pipe. Drill a hole in the top of the pipe, and the bucket sits on top. Space the buckets along the drainage pipe and feed the individual plants using a vinyl tube with small inline valves. Place a timer on your pump to deliver nutrients several times a day. This system is ideal for both larger plants and fruiting plants. With a larger amount of substrate, they can be in place for long periods of production. They will need support from above from a string or trellis, and you may need a ladder to continue to pick. This is not an exaggeration — think 8-foot-tall kale and Brussels sprouts!

A Deep Water Culture (DWC) raft uses a rectangular tank with flow and aeration from 6 to 12 inches of nutrient solution. Rafts cut with holes float on the surface of the nutrient solution. Small seedlings — mostly leafy greens — are placed in the holes, and roots extend through the raft and into the water column. These systems are common in commercial projects. Rafts are typically 2 by 4 feet, and mature plants are harvested out of the rafts at one end of a rectangular tank. At the other end of the tank are seedlings that are loaded in after the floating rafts are pushed down to the harvest end. With a 2-inch seedling, mature lettuce can be harvested in just 35 days.

Dutch buckets hold huge Brussels sprouts supported with trellis lines to hold them.

Block and slab systems are a fourth option. These systems most often have been used with Rockwool; however, there are new products out there using coco fiber or coir. Both are inert and provide a basic substrate for feeder roots to grow through while the nutrient solution is delivered to each plant with an individual flexible tube. This is about graduation from one substrate block size to the next. Starting with a seedling grown in a 2-inch starter plug, it is then transferred to a 4-inch-square substrate block and fed nutrients to make a larger seedling. As roots begin to fill and explore below the 4-inch block, it is then graduated to a larger block or slab for the rest of its growing life. Three or four plants can be placed on a single slab. Rockwool products come in a variety of sizes and arrangements — from 1-inch plugs to 8-inch slabs — and are wrapped in plastic to protect against algae production and direct the fluid horizontally before allowing it to escape and drain to the reservoir. These slabs can be placed on a “flood table” to capture and drain water back to the reservoir. Commercial operations generally use a large gutter on a stand to capture and return nutrients to the reservoir, with the slab directly over the gutter. Since these may grow larger fruiting plants, trellising above the plants is required for support. This style can be really rewarding even on a small basis.

Finally, flood and drain table setups are shallow table tanks supplied with a sump. Mature plants and large seedlings are produced in this manner, as are microgreens. The type of container varies from thin slabs of rockwool to grow microgreens to large containers with bottom holes using a coco fiber mix. At timed intervals, a nutrient solution is pumped in through a screened inlet in the table, flooding to a desired level determined by a small standpipe and draining back to the reservoir. The flooding overfills for a portion of time with the nutrient solution. When the pump turns off, the solution drains out. The unique part of the installation? The pump has no check valve, and the nutrients drain completely out of the table through the pump and associated plumbing. The screened inlet prevents water spray on the way in and protects the pump and reservoir from accidentally receiving any debris from plants on the table. The standpipe simply controls the water level during the filing interval.

So, What Can You Grow?

The list is long — fruits, vegetables, ornamentals, you name it. The Netherlands uses a lot of hydroponic technology, and that tiny country, for the most part, feeds the entire continent of Europe.

I think this technology, although increasing in popularity, is still way underutilized in STEM education programs and in science and agriculture classes in schools. Most of the professionals in the water feature and koi pond industry are already innovative and enjoy water engineering. Hydroponics, small or large, will likely be something you will enjoy.

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