Square foot considerations

Photos by John Bartok Jr.

Growing space is expensive. One excellent way to reduce production cost per plant is to make better use of greenhouse space. The cost of providing heating and cooling is the same, whether you utilize 50% of the space or 100%. Every square foot that has plants means additional dollars of income. The following are 10 ways in which growing area can be increased.

1. Peninsula benches

Conventional lengthwise benches typically cover about 60% of the floor area. The remaining 40% is for aisles to access the plants. Changing to a peninsula arrangement that places the benches perpendicular to the sidewall with 18-inch work aisles between and one 3-foot to 5-foot main aisle down the center will increase growing space by at least 10%. This system also provides easier access for moving plants with carts or conveyors.

2. Movable benches

With this method, up to 90% of the total greenhouse area can be covered with benches. Two types of systems are common. The simplest is to install the benches that remain in the greenhouse but move sideways on rollers placed over a support frame. By moving the benches, a single work aisle can be located wherever it is needed. The steel rollers create very little friction, and a 100-foot bench can usually be pushed by hand.

A more efficient system from a labor standpoint is the movable tray system. Modular trays, usually 6 feet wide by 8 to 20 feet long, are moved to and from the growing area on rails, carts or conveyors. Transplanting, loading and unloading trays are done in a headhouse area, where everything is more convenient.

3. Roll-out benches

You can double growing space by placing one layer of plants on a heated floor and a second layer 20 to 30 inches above the floor on a pipe support system. During the day, the trays are rolled outside the greenhouse onto a matching pipe network. Both crops receive full sunlight. At night, they are rolled back into the greenhouse. This system can be adapted to both hoophouses and gutter-connected ranges. The system is good for hardening off bedding plants during the spring and for potted plant production during the fall.

4. Floor production

It is a common practice to leave only one narrow aisle down the center of the greenhouse. Space utilization is almost 100%. This low-cost system can be improved with heated floors and boom watering. Access is only needed to observe the plants. When shipping time arrives, a work aisle can be created by removing the plants out of the center of the greenhouse first.

Flooded floors: A modification to the above system being adopted by larger growers is the flooded floor system. Although the concrete floors, pumps, tanks and controls cost more, plant production is very uniform due to the even watering. Handling of the plants is best accomplished with a gantry that straddles the width of the bay or with a fork truck.

5. Racks

If you are growing hanging baskets or larger potted plants, an A-frame rack system can double your growing space. Racks are especially effective where foliage plants are grown, creating conditions similar to a forest canopy. They can be built with 2-by-4 lumber and fence pipe or with heavy steel rods. Racks can be made movable but are usually fixed to the floor or overhead trusses. If you are going to suspend the racks, be sure that the greenhouse frame is strong enough.

6. Hanging baskets

Many growers place containers over part of their growing area to increase space utilization. In taller greenhouses, two or three tiers of baskets may be suspended. These baskets are fitted with an automatic watering system, and the spacing depends upon the light requirements of the crop on the floor or benches beneath.

A more efficient system is the hanging basket conveyor, which is attached to the overhead trusses in the greenhouse. Plants spaced as close as 8 inches apart are supported by a conveyor that moves them past work and watering stations. The savings in labor of having plants brought to an aisle for placement, inspection and shipping can offset the cost of the system.

7. Under bench production

A few growers utilize the space under benches as a production area. It works well for crops like groundcovers. By adding LED strip fixtures, other low-light crops can be grown. But note that watering is more difficult, and there could be increased disease problems.

8. Utilize aisles and walkways

I have been in many greenhouses where wide aisles were installed to allow for customers during the busy retail sales period. In gutter-connected houses, these are sometimes 10 to 12 feet wide. An aisle this wide is seldom needed except during shipping time, and some of this space could be filled with plants on the floor, benches or racks.

9. Movable greenhouses

A trend by growers using high tunnels for vegetable production is to install low-cost movable greenhouses. One area is used for early season production of greens. When the weather warms up, the greenhouse is moved to the adjacent area for warm season crops, such as tomatoes and cucumbers. The greenhouse frame runs on rails or skids and is moved with a tractor or winches. These structures may also have applications for protection of perennials and herbs during the winter and for cool temperature production during the winter.

10. Removable hoophouses

The space allowed for snow accumulation between free-standing greenhouses could be set up with hoops that are covered with plastic after the threat of snow is over. This space is the most valuable during late spring just before shipping season begins, when the conventional greenhouse space is overflowing and there is a need to harden off plants. A little heat could be added, possibly from the adjacent greenhouse.

Today, as energy costs increase, good growing space utilization is important. Making use of some of the above systems, keeping growing space full and providing optimum environment control can help to produce plants at the lowest cost.