Hanging around

Movable benches can provide more than 90 percent space utilization in a greenhouse; adding hanging baskets can increase space utilization to well over 100 percent. With energy costs increasing, the more plants that can be grown per unit area, the greater the economic return.

Hanging baskets intercept considerable light, reducing the light level on the benches or floor underneath. This needs to be considered when selecting plants and determining the time period when they will be grown. Consider the following before growing a hanging basket crop.

The greenhouse structure (glazing, frame, heating system, etc.) reduces light level at the plants by 40 to 70 percent. There is generally more reduction from the structure and utilities placed overhead than from the type of glazing used, so it is important to place heating and water pipes, conduit and light fixtures where they create minimum shading.

Taller greenhouses provide less direct shade because the structure is further from the plants. This is one reason why many gutter-connected houses are now being built with 16-foot to 20-foot gutter height.The heat loss from the extra surface area only amounts to several percent in large houses. Although having less structure, hoop houses could also benefit from increasing sidewall height by a foot or two.

To help in deciding what plants will do well and when, a determination of the percentage of light that reaches the plants is important. A quantum sensor is best, but a foot-candle meter will also work. Measure light level outside the greenhouse and inside at the plant canopy. It is best to do this on a cloudy day, when the light is more uniform. Substitute the values in the following formula:

For example, if the reading is 4000 foot-candles inside and the reading is 6000 outside the calculation would be:

Determine the average Daily Light Interval (DLI) for the time of year when the plants will be grown. DLI is a sum of the total light received at your greenhouse measured in moles/day. It is easiest to obtain this from DLI maps -- see www.specmeters.com/assets/1/7/A051.pdf. These charts provide average DLI by month. This research on light requirements of plants was done by Dr. James Faust and others at Clemson University.

Low-light plants require 5 to 10 moles/day and grow best with cool temperature. Moderate-light plants require 10 to 20 moles/day. This is best for most potted plants and gives normal growth and flowering. High-light plants (20 to 30 moles/day) are mainly herbaceous perennials that need this amount of light to get bushy foliage and high flower numbers.
 

Small hanging basket plants do not require a high light level to achieve a maximum growth rate. The light level under a crop of hanging baskets decreases as the plants grow, but it will be offset somewhat by increasing day length and light intensity as spring progresses.

Light-colored pots reflect more light and transmit more light to the plants below. For example, there is approximately a 5 percent increase of light under a crop of white pots as compared to green pots.

A multiple layer system will create about the same amount of shade as placing the same number of baskets in a single layer. This is because the rows of plants are spaced farther apart and more light gets through. A north-south orientation of the rows is better, as it provides a moving shade pattern on the plants or floor below.

More information on the effect of light on plants can be found in the “Lighting up Profits — Understanding Greenhouse Lighting,” edited by Dr. Paul Fisher and Dr. Eric Runkle.