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Build Your Own Hydroponic Treeby Les Bridgewood

It's not hard to do. And once you have it, you can grow your own strawberries and flowers for months and months.

This hydroponic grow unit I describe here will make an ideal growing unit for small plants, such as flowers or strawberries, in the house, in the conservatory, on the patio or on a roof garden.

If the hydroponic tree is planted with strawberry plants such as 'Calypso', these plants produce continuously outside from July to first frost in the United Kingdom, and in the greenhouse almost right round the year. The right type of plants with good air conditioning, a little warmth and good light can provide a good crop of strawberries right through the summer, even through to Christmas. Alternately, with a good mix of flower plants you can have that very welcome splash of color with a minimum of effort.

The construction is very simple, using items purchased from a do-it-yourself (DIY) building store and hydroponic suppliers. The tree is made entirely from plastic, as metal must not be in contact with the solution. In the flower tree, a 240-volt submersible pump runs in a hydroponic nutrient solution. The solution must be made up using a hydroponic mix of nutrients. To prevent an imbalance of the nutrients occurring over time while the system is in use due to the plants removing some elements and leaving others, the solution should be replaced with a new mix when 3 gallons (the original capacity of the tank) of the same strength solution have been used to top up the tank, but it is not necessary to bother about a gallon or so. Solution used by the plants or due to evaporation must be replaced as the level falls. A 4-watt air pump arranged to aerate the solution in the main part of the water tank will prevent the solution here stagnating. The normal flow of the solution is to circulate up the soil pipe and around its base with the rest of the solution acting as a top up.

A 4-watt pump running continuously for one full year would consume 35.04 units of power, in a leap year 35.136 units, a very small cost and no watering problems. Twice this if an air pump is used.

Planted with a collection of flowers 4 to 6 inches (10 to 15.2 cm) high or hanging basket flowers the tree gives a really colorful display to brighten up any area with natural or artificial light available. With hydroponics most plants can be grown, even plants requiring acid conditions, a drop of phosphoric acid in the solution will take the pH down or drops of bicarbonate or potassium hydroxide can raise the pH.

Light from a high efficiency fluorescent lamp, providing light on dark days in winter could be helpful.

Shopping list:

The tank and pipes I have used are all black. The flower tree can then be used year after year.

Construction Details

Tools used were a round file, a drill, a hacksaw and a strong pair of scissors. The plastic is an easy material to work with. Construction only took around half a day.

  1. Reduce the height of the 4-gallon (18.21-liter) water tank to give a total height of 8 inches (20.3 cm) by cutting the top off with a hacksaw.
  2. The soil pipe (sold as a Marley soil system with seal socket) has a flange on the base with a rubber gasket in. The rubber gasket is removed and a 2-inch wide by 1-inch-deep slot is filed on the base of the flange. This allows the solution in the tank to flow under the base of this soil pipe while the flange of the pipe is sitting flat on the base of the water tank.
  3. On one side of the soil pipe, drill four holes 1.25 inches (3.2 cm) in diameter and 6 inches (15.2 cm) apart on each side and in a line from top to bottom in the 2 foot, 4-inch (71) high pipe. Stagger three holes in a line top to bottom on both sides of the first line of four holes. This gave me 14 planting holes in total.
  4. Make a plastic filter by drilling lots of 0.125-inch (3.2 cm) holes in a round piece of plastic. I found the base of a plastic jug did this job. This filter should be a reasonably good fit in the soil pipe to sit on the ends of the four plastic bolts, which will protrude into the 28-inch high pipe. The function of the filter is to prevent the media in the soil pipe coming in contact with the pump while allowing the solution to return freely to the tank.
  5. The 9-inch (23 cm) length of 2.75-inch (7 cm) diameter pipe is cut into three lengths 3 inches long (7.6 cm), a length is attached vertically to the soil pipe on three sides. The same three 3 inch (7.6 cm) lengths of pipe will be attached to three sides of the tank later. This is to secure the soil pipe vertically in the tank. Plastic nuts and bolts are used for this operation.
    Fit the bolt heads inside the 3-inch (7.6 cm) long lengths of pipe and extend the bolts through the soil pipe and secure with a nut. A fourth plastic bolt is placed level with the other three in the soil pipe to give support to the filter. The filter will sit on these bolts when it is fitted later.
  6. The pump with a length of hose and a fountainhead attached is sited out of sight inside the flange of the soil pipe. The pipe from the pump is passed through the middle of the plastic filter, which rests on the four protruding plastic bolts. This pipe carries on up the center of the soil pipe almost to the top of the soil pipe where it terminates on a fountainhead. This is to spread the solution over the growing media. The total length of the hose from the pump, including the fountainhead, must be around 27.25 inches (69 cm). This is quite important, as the head of the pump is only 2.3 feet (0.7 m). Exceed this height and no solution, or very little, will leave the fountainhead at the top of the hose. Make it a lot less and you really will have a fountain.
    The height of the solution in the tank above the pump gives a good deal of control over the flow from the fountainhead; it has the effect of changing the head of the pump. This is very useful and can be used to give the desired flow of solution leaving the top of the pipe. Start with a level of solution that will give a good flow (a small low fountain).
    As the plants use water and nutrients the level will fall and the flow will be reduced. More solution of the same mix should then be added restoring the original flow. The rate of flow is not critical as long as the filter resting on the plastic bolts, along with the porosity of the media used, can pass the solution without flooding the unit. The minimum flow should maintain the media in a damp state. The pump should be obtained from a hydroponic supplier.
  7. Fit the pump into the base of the soil pipe and connect the pipe between the fountainhead and the output of the pump. Check that the slide on the side of the pump is set to maximum flow.
  8. Now secure the 3-inch (7.6 cm) lengths of plastic pipe that are secured to the soil pipe, to three sides of the tank using three more plastic nuts and bolts. This secures the 2-foot, 4-inch (71 cm) soil pipe vertically in the water/solution tank
  9. Now make a lip for each planting hole. Cut a piece of 2.75 (7 cm) inches (outside diameter) plastic pipe into two-inch lengths. Slice each piece into two sections lengthways. Shape the two pieces as shown in the photo. It looks like a rounded tongue with a clip at each side on the rear. These 2-inch lengths form the lips. Squeezing each across its width while holding it at an angle of 45 degrees up, insert one into each planting hole and push it in. Quick-grips may be required. Release the pressure across its width and the plastics will spring open, gripping the sides of the planting hole while the clips will clip onto the inside of the Marley soil pipe. Placing epoxy resin right round the underside of the lip will secure them to the Marley soil pipe and make a seal.
    These lips are required, as some plants (like strawberries) do not like the neck of the plant to be wet and also the solution is deterred from running down the outside of the tree. The plants rest on this lip with the roots in the media.

Putting Plants in Place

Pre-soak the perlite and the clay balls in the solution to be used for 12 hours. Remove as much dry media as possible from the plant's roots (assuming the plants have been bought in), then holding the plant gently by the stem move the roots up and down in warm water (25 degrees C) to remove the rest. Take care with the roots; don't wait for the plant to shout.

Using a mixture of one part perlite to three parts clay balls, place a layer of pre-soaked media on the filter in the soil pipe up to the level of the first planting holes. Put the first layer of plants in position, avoiding air pockets around the roots. The coarse nature of the media ensures oxygen is available to the roots at all times but moisture must be available also. Cover the roots with media and continue up the soil pipe planting in this way.

If a mixture of the solution strength being considered can be used to wash the media into position using a watering can this will reduce the chance of air pockets round the roots. Repeat this a few times, each time the contents of the tank are emptied the contents should go onto a few deserving soil-grown plants. This procedure also removes a lot of dust off the new media; good drainage is very important.

When planting is complete make a mound of clay balls over the fountainhead. Put some perlite round the mound and plant more flowers or strawberry plants.

The flow from the head is not critical, as long as the filter can pass the flow without flooding and the media is kept moist, then all will be well.

Use concentrated packs of nutrients from hydroponic suppliers. I have found Ionic to be very good (it is a single mix of liquid nutrients). It is available as grow or bloom to suit the growth required. If you do not mind adding two equal measures of two mixes (known as pack A and pack B), then these also come in liquid or powder form and are also available as grow and bloom. The supplier of the nutrients will recommend the number of ml of nutrient to add to one liter of water.

If you intend to grow flowers with artificial light in a cool area, a small glass aquarium heater can be placed in the solution to heat the solution to around 22 C. A clean house tile placed between the heater and the plastic will prevent heat damage to the plastic tank. Take extra care to prevent the solution level falling below the heater. A live or warm glass tube heater will crack when it is part out (or right out) of the solution with bad consequences. Always fit a 30 mA trip unit in series with any mains item in solution or water. Avoid heat losses through the ground by having polystyrene insulation between the floor and the tank.

Les Bridgewood is a hobbyist grower and freelance writer in the United Kingdom.

For the complete version of this article, see The Growing Edge, Volume 17, Number 3, January/February 2006, page 38.