Hydroponic Tomatos

December 24, 1996

Recently a Model KP-6 screw press was tested on cull tomatos at Vine Ripe in Owatonna, MN. This firm serves the Twin Cities with premium quality tomatos. They have four acres of greenhouses, to which they are in the process of adding three more. Dutch firms dominate in the growing technology, so the greenhouses are imported, knocked down in cargo containers, from Holland. Dutch crews erect the houses, with only the glass windows being supplied locally.

The greenhouses use glass as it is far more durable than plastic film and it does a better job of transmitting light.

The vines are rooted at ground level in rock wool batting, roughly three inches thick by twelve inches wide. There is no dirt used in the production process. Food for the plant is supplied by a drip irrigation system that feeds nutrients and water directly onto the rock wool.

A tomato plant will yield fruit several years. However, because yield tends to fall off, the plants are replaced once a year in Holland. In Minnesota, because of the adverse and varying weather conditions, the plants are replaced twice a year.

The tomatos are harvested continuously, except during the months of January and February. These months are skipped, even though November and December are the coldest months, because window frost in January and February reduces the sunlight that reaches the plants.

The greenhouses are equipped with rails between each row of plants. These guide electric carts that are used for weekly maintenance and harvesting of the plants.

Weekly maintenance consists of attaching plastic clips to hold the vines to strings that are suspended from the ceiling beams of the greenhouse. The vines grow to be thirty-five feet long. The clips are about a foot apart, roughly the length grown each week. Also, arched plastic supports, called trusses, are attached to the vine where there is a branch with tomatos. This allows the tomatos to grow without dragging down the stem to which they are attached.

Bumble bees are kept in the greenhouses to provide pollination. Without pollination, the tomato does not have seeds and it grows to a dwarf size. The bumblebees eat some pollen as a source of protein. Sugar water is kept in their hives so as to provide other nutrients. The bumblebees do not make honey as the tomato flower does not have sufficient nectar.

Pest control is critical. One factor that add difficulty is that special insecticides must be selected to prevent killing the bumblebees.

Large hydroponic operations are found in states such as Arizona and Texas where up to 300 days of sunlight are available per year. A typical large operation would have 40 acres of greenhouses.

The flow rate through the Vincent KP press was excellent. In pressing the cull tomatos we found it easy to achieve a separation of 50/50 between press liquor and press cake. The cake is suitable for composting, and it was hoped that the liquor could be sewered. Most of the seeds ended up with the press cake.

The reason for pressing the cull tomatos is to reduce the charges for hauling the tomatos to a disposal site.

Issue 53