Semi-Hydroponic Gardening

Growing garden produce in a greenhouse is a space-saving way to ensure very long season production. Growing in the ground itself, though, is very limiting for the space available.

To gain maximum food production from a limited space, growing edible plants on shelving along greenhouse walls is a way to maximize the potential cubic footage available under cover. And "under cover" means protection from weather extremes, tertiary fallout and most pests.

Hydroponic gardening is defined as using an inert media as a root-holding material, with all nutrients being supplied via water. Such a system is usually expensive to build and maintain, as pH buffers, fertilizers and nutrients must be purchased from specialty suppliers. The root-holding material is often an expanded rock, spun rock wool, or something similar. The water is circulated by means of electric pumps. I consider pure hydroponic gardening to be a very fragile system because it relies on electric pumps to circulate the water and generally all supplies must be purchased at considerable cost.

With worldwide famine a very real possibility in the near future, mistakes in our individual food supply cannot be tolerated! That eliminates pure hydroponic gardening.

On the South side of each greenhouse I built tables, then had a sheet metal shop build a tray with 3" high sides and a 3/8" drain in the center of one side, near the bottom. That way I can simply flood the tray to water the plants, let it sit for a day, then drain out the water through the ball valve.  The soaking trays above look a little beat up, but I've been using them for twenty years!  Once built, infrastructure can last for a very long time.

There is an alternative: semi-hydroponic gardening. Modified soil can be used to hold plant roots and inexpensive trays can be built to hold planting pots in a little water. The concept is relatively simple.  The trays are filled with an inch of water, the soil "wicks" the moisture up to the plant roots, yet the top of the soil remains relatively dry!  The roots are encourage to grow down, and the dry soil on top discourages damp-off and other diseases caused by excess moisture.

MODIFIED SOIL

An inert media such as expanded rock is used in hydroponic gardening because the porous rock does not retain too much moisture, a fault of most soil. In semi-hydroponic gardening, very fine sifted topsoil is mixed with compost, peat moss, vermiculite and pearlite in about equal proportions. Half the "soil" is then vermiculite and pearlite, so drainage is pretty good, yet full capillary action is maintained.  Home made compost can be added to the soil mix as needed, and the "soil" mix used over again in the lower 2/3rd of a pot, saving considerably in the cost of this method.

Before filling pots with the soil mix, grass clippings are placed a few inches deep in one gallon pots and four inches deep in 30 gallon pots.  The grass clippings will compact and compost, adding to the soil mix, but before that happens the grass clippings will act as a filter, keeping dirt inside the pot and not flowing through the drain holes in the bottom of each planting pot!  Note the pots are on carpeting, which eliminates excess dust and soil-borne diseases.

 

THE SOAKING TRAYS   For wall shelving

"Standing seam" roofing metal makes excellent soaking trays.  The metal  has formed edges for strength, is 16" wide, and can be any length required.  The ends are bent up and sealed, making a tray 1 1/2" deep to hold water.  One gallon (9") pots will hold the soil which holds the roots.  The water in the tray is drawn by capillary action up through the soil to the roots, encouraging the roots to grow down to the bottom.  The soil itself is never watered!  Being relatively dry on top, there is no inducement for damp-off or diseases caused by overly wet soil.  The left photo above shows cabbage growing nicely, and the right photo shows chard and lettuce beginning to grow.  The shelves are just over 3 feet wide, with 20" of overhead space between shelving.  Six shelves of two rows yield 36 linear feet of 18" wide shelving, yet only takes up 18 feet of space along one wall of the greenhouse!  That is enough to provide all the greens for a family of four up to 10 months of the year.  The floor space of the greenhouse can still be utilized for root crops, even growing well in 30 gallon pots that can be used year after year.  And all under cover, safe and secure.  The photos above show "standing seam" trays, 3 feet long, on shelving in my large greenhouse. 

"Standing seam" roofing metal is also excellent for use as a transplant starter tray.  A 4 foot tray will hold 30, 4" pots. After a month, the plants are ready for transplanting and new pots and seeds are started for a continuing maturity.
This 4 foot tray is made from standing seam roofing metal:  I put up a 4 foot fluorescent fixture with grow lights, hanging by small chains at each end. The fluorescent shop light can be lowered to provide additional light to spur growth of seedlings, and raised when watering or not needed in late spring.

THE SOAKING TRAYS   For 30 gallon pots

A photo above shows 30 gallon pots lined up in the middle of the greenhouse floor.  Those pots will grow root vegetables such as beets and potatoes.  Carpet remnants are first laid down to cover all the soil in the greenhouse.  That inhibits soil-borne diseases, eliminates any mud or debris, etc. 

Placed in a soaking tray along a wall, 30 gallon pots will grow tomato plants of incredible size.  The photos above show tomato plants against an 7 foot fiberglass wall - and they have reached the fiberglass roof and spread back 3 feet along the roof!  It is hard to photograph green-on-green and get good detail, but the photo on the right shows the yield.

   

Photo at left shows an old 30 gallon pot in a 25" section of standing seam metal roofing. Most 30 gallon pots are 14" wide at the base, so they will easily fit into the 16" wide standing seam roofing. Tin snips are used to cut 1 1/2" tabs on each side of each end. The flat bottom is then bent vertical, the tabs bent in around the new ends and sealed with silicone glue. A waterproof soaking tray can be made at very little cost because roofers throw away pieces this short.  Soaking trays made from standing seam roofing metal can be to any length, but lengths 4 feet or less are easier to handle.