Starting an Outdoor Hydroponic Garden

Indoor gardening can get expensive in the heat of the summer, especially if you’re constantly running air conditioners and dehumidifiers. Why not take advantage of all the free sunlight nature has to offer and start an outdoor hydroponic garden? Outdoor hydroponics still provides the perfect balance of water and nutrients, and your plants will grow much faster than in soil. Plus, there’s no weeding! Here are a few tips to get a summer hydroponic garden started.

Choose a Sunny Location for Your Hydroponic Garden

There is no substitute for full-spectrum summer sunlight, and best of all, it’s free! Even a 1,000W lamp, placed a foot from your plants, can’t compare with a sunny day in mid-July. So when setting up an outdoor hydroponic garden, pick a sheltered area with a good southern exposure if you can. I’ve grown prolific amounts of basil in a nutrient film technique system in a parking lot, towers of aeroponic herbs and strawberries on my back porch, and a huge row of tomatoes in stonewool in front of my garage. The vines grew so dramatically that strangers driving by would stop their cars, knock on my door and ask me how I was making the tomatoes grow so fast! They were amazed when I showed them my hydroponic systems. By the end of the summer, the vines were growing up to the roof and I had a wall of gourmet-quality tomatoes.

Keep the Water Reservoir Cool

Plants will transpire a lot more water in the outdoor heat than when they are grown indoors, so make sure you top off the reservoir with cool water from your garden hose often. It’s also a good idea to keep the reservoir in the shade whenever possible. In an ebb and flow system, it’s easy because the reservoir is underneath the flood table anyway. But if the reservoir is somewhat exposed, I like to at least partially bury it if I can. The earth acts as a natural heat sink to pull some of the excess heat out of the reservoir. On the hottest days of the summer, adding a little ice to the reservoir can help. Keep a couple of two-liter bottles of water in the freezer, and drop one into the reservoir occasionally. If you walk by later in the sweltering afternoon and you notice the ice has melted, put the bottle back in the freezer and drop in another. Luckily, the worst heat waves usually don’t last more than a few days, so such emergency measures are rarely needed.

Lower the Electrical Conductivity (EC)

In hot weather, it’s best to lower the EC of the nutrient solution. For example, if I normally keep the EC for my lettuce-growing system at 1.2, I’ll lower it to 1 in the summer. Plants are thirstier in the summer, so doing everything possible to make it easier for them to take up water is a good thing. Low-to-medium EC stimulates vegetative growth by making the nutrient solution less salty, while medium-to-high EC restricts vegetative growth. During the heavy fruiting and flowering stage, a little salt stress is good, but watch your plants carefully. At the first sign of browning at the edges of the leaves, lower the EC a little more.

The worst thing that can happen to an outdoor hydroponic garden is to let the reservoir run dry. Plants won’t last long in the summer sun without water. It might be a good idea to add a float valve to your reservoir as an insurance policy. If the water level gets too low, the float valve will open automatically and top off the tank with fresh water. Plants can go a few extra days without fertilizer, but they will only last a few hours without water. Plan ahead so you can enjoy a few days away at the beach when you want to.

Boost the Heat Tolerance of Plants

The best time to condition your plants against stressful situations is before the stress happens. In the earlier part of the summer, try adding a combination of humic acid and kelp extracts to your nutrient solution. A 10-year study at Virginia Tech showed that humic acids combined with seaweed extracts work 50% better than either product alone. A 5:2 ratio of humic acid to kelp works best to greatly stimulate lateral root growth and improve overall root mass. When the summer heat comes, the more roots the better for taking up the extra water they need.

The humic acid/kelp combo also encourages the plant to make extra plant-protection agents. Under ideal conditions, plants have no trouble protecting themselves from cell damage, but when plants are under too much stress, they can’t keep up with the constant barrage of damaging free radicals. Free radicals break down cell membranes such as chloroplast and mitochondrial membranes, which is why plants go from green to yellow to brown under excessive heat and UV light. If you condition your plants against stress with a combination of humic acids and kelp, plants will produce 50% more of the protective molecules that sponge free radicals, and plants will stay green longer when the summer heat arrives. Remember to condition the plants before it gets hot—if the plants are already suffering in the middle of the summer, the bio-stimulants won’t have enough time to help.

Ensure Air Movement

Air movement is important, especially in the summer. One of the advantages of outdoor hydroponics is the breeze. The air movement helps cool the plant and keep the stomata open. Stomata are the pores in the leaves that take in carbon dioxide and transpire water vapor and oxygen. As the breeze takes away the water vapor from the leaves, it has a cooling effect on the plant.

Too much wind has the opposite effect—plants close their stomata to conserve water so they don’t dry out too fast. Outdoors, we don’t have much control over the wind, so try to grow in a spot that has good air movement but also provides a protective wind break. Planting along a fence row with southern exposure is a good choice. Also, think ahead about what you will do if a major storm approaches. I’ve learned the hard way how important it is to properly stake my plants and provide a little extra emergency protection.

Protect Against Pests

One down side to growing outdoors is that you often have to share your crops with animals and other pests. The simplest advice is to fence in your garden or grow a few extra plants and hope the critters don’t get too greedy. If you’re not willing to share, there are other deterrents available at your hydro store such as wolf and coyote urine (I’m serious!) that help keep rabbits and other invaders away. There are also some good natural sprays such as neem oil and insecticidal soaps that help fight bugs and act as natural insect repellents.

But the best defense against pests, particularly sucking insects, is to grow healthy plants. Use full-spectrum fertilizers, and keep the potassium-to-nitrogen ratio high. Too much nitrate nitrogen produces large cells with thin cell walls, making them an easy target for sucking insects and fungi, so don’t over-fertilize. For even healthier plants, try using a bio-hydroponic fertilizer that combines minerals with organic bio-stimulants. For example, amino acids stimulate the uptake of calcium.

Due to the extra calcium intake, plants grown with amino acids have thicker cell walls and a higher resistance to temperature extremes. The plants will also have a stronger vascular system, allowing them to take up water and minerals more efficiently. It all adds up to nutrient-dense, high-brix plants that have an increased resistance to pests and diseases. If all goes well, sucking insects won’t even recognize the plants as food.

Just wait until you taste what a well-managed outdoor hydroponic garden can produce. Healthier plants mean tasty, nutrient-dense food high in vitamins and minerals. Colors and aromas are also much richer, and you can literally see the difference in growth from day to day. It’s hard to imagine just how productive an outdoor hydroponic garden can be until you try one for yourself!

By Harley Smith