Potting Soils PERLITE

Comparative Study
Perlite Vs. Polystyrene
PLANT GUIDE
The Schundler Company
150 Whitman Avenue
Edison, NJ 08817

732-287-2244 www.schundler.com



COMPARATIVE GROWTH STUDIES
PERLITE VS. POLYSTYRENE



Original research by
O.A.Matkin
Soil and Plant Laboratory
Santa Ana, California

Previous measurements of physical properties of growing media comparing perlite with polystyrene beads have indicated higher density and moisture retention when perlite is used in the growing media. Since high moisture holding capacity combined with adequate aeration is an important asset in container production of plants, trials were carried out comparing ryegrass growth in mixes of the two amendments under a series of watering schedules. Composition of the two amendment mixes is shown below:


Perlite Media
0.5 cu. yds. Perlite
0.5 cu. yds. Sphagnum Peat Moss
5.0 lbs. Calcium Carbonate Lime
3.0 lbs. Dolomite Lime


Polystyrene Media
0.5 cu. yds. Polystyrene Beads
0.5 cu. yds. Sphagnum Peat Moss
5.0 lbs. Calcium Carbonate Lime
3.0 lbs. Dolomite Lime

Watering Schedule Varied

Containers used in growth trials were 6 inch plastic pots, 20 for each mix, 1400 milliliters of mix per pot. All pots were seeded with perennial ryegrass at the same time and maintained most for one week at which time uniform germination had occurred. Beginning with the second week, the watering schedule was varied according to the schedule shown below:

Perlite A & Polystyrene A
Perlite B & Polystyrene B
Perlite C & Polystyrene C
Perlite D & Polystyrene D
Every Day
Every 2 Days
Every 3 Days
Every 4 Days

The water that was applied contained as balanced soluble nutrient and was supplied to each pot in the amount of 500 milliliters per pot at each scheduled irrigation. The excess liquid from each pot was collected and returned to the pot and drainage water was again collected, volume measured and recorded before discarding.


"...SAMPLES PLANTED IN POLYSTYRENE BEAD MIX AND WATERED ONCE EVERY 4 DAYS FAILED TO PRODUCE ADDITIONAL GROWTH AFTER 12 WEEKS."

Clippings Weighed

The use of ryegrass as the test crop permitted successive harvests at which time clippings were dried and weighed. Harvests were made a t 4, 8, 12, 16, and 20 weeks.

The maximum volume of water retained after drainage was determined to be 583 milliliters for the peat/perlite mix and 383 milliliters for the peat/polystyrene bead mix (1400 milliliters volume of mix).

During the course of the growth trials, some unusually high temperatures occurred in the greenhouses which placed severe stress on crops under the limited irrigation regime. The five ryegrass samples planted in a polystyrene bead mix and watered once every 4 days failed to produce additional growth after 12 weeks.

Results

Growth, as measured by quantity of clipping yield (see curve), was best in most frequently watered samples. Visual inspection confirmed parallel root development. The order of growth rating from highest to lowest was: Perlite A, Perlite B, Polystyrene A, Perlite C, Polystyrene B, Perlite D, Polystyrene C, Polystyrene D.


"PERLITE CONTRIBUTES TO MOISTURE SUPPLY OF THE MEDIA TO A GREATER DEGREE THAN POLYSTYRENE BEADS."

Moisture utilization followed the same pattern that was noted for growth. Rating from highest moisture utilization to the lowest was: Perlite A, Polystyrene A, Perlite B, Perlite C, Polystyrene B, Perlite D, Polystyrene C, Polystyrene D. Differences between Polystyrene A and Perlite B were minimal. Thus, irrigation every other day in the perlite mix was equivalent to irrigation every day in the polystyrene mix, and irrigation every 3 days in the perlite mix was equivalent to irrigation every 2 days in the polystyrene mix.


"...POLYSTYRENE BEADS ARE INFERIOR TO PERLITE AS AN ADDITIVE IN GROWING MEDIA."

Conclusions

Growth and water use as measured in this set of studies confirm previous physical measurements of mixes prepared with perlite and polystyrene beads. Perlite contributes to moisture supply of the media to a greater degree than polystyrene beads. For some reason, growth was superior in Perlite B compared to Perlite A, both of which were provided about the same amount of moisture. Apparently, some other restricting factor in the polystyrene bead mix limited growth. Under conditions of high stress (irrigation every third or fourth day), perlite media out-performed polystyrene bead media.

From these technical reasons, and the obvious environmental problems, polystyrene beads are inferior to perlite as an additive for several reasons.


For more information, contact:
The Schundler Company
150 Whitman Avenue
Edison, NJ 08817

(ph)732-287-2244 (fax) 732-287-4185
www.schundler.com

Back to Horticultural Main Page