The use of horticultural perlite in the container and hydroponic industries is well known, and few potting soils designed for home or professional use are manufactured without it.
Perlite is plentiful throughout the world. A naturally occurring and then expanded volcanic glass, perlite has no known health hazards, and serves traditional horticultural uses by providing both aeration and water retention (up to 450 % by weight and 75% by volume).
Its use in the American landscaping and turf industry, however, is extremely limited in spite of extensive, historical testing and usage in countries like Japan and India where turf grade perlite has been used for water retention and the prevention (or delay) of damage from compaction.
During the 1950's and early 1960's, The University of Tokyo conducted extensive research for Mitsui Mining and Smelting Co., Ltd. The goal was to study the effects of adding perlite to heavily used golf courses and turf grasses in a climate where rain can be limited and proper irrigation costly.
Among the studies conducted were those focusing on the effects of "trampling" or compaction, and draught---two of the major problems for Japanese gardens, parks, and golf courses. Most of the studies were conducted with Koraishiba (a variety of zoysia Matrella MERR), Astoria bent (a variety of Colonial bentgrass or Agrostis tenuis SIBTH), and Italian rye grass. The results showed again and again that trampled and non-trampled plots using perlite had increased growth, improved tiller production, and better root production. In fact, in some of the test the trampled perlite plots did far better than the non-compacted control plots.
Water Conservation
With water conservation becoming an ever-increasing concern among turf managers and landscapers, the results of the Japanese wilting test are perhaps even more interesting. Essentially Italian rye grass was grown in eight different potting media ranging from sand and reddish loam soil, to blends of soils with perlite, to 100% perlite (both large particles and small grades of perlite were used throughout these test.)
"After the seedings were completely rooted, the soils were saturated once with distilled water. Irrigation was then stopped, pots were allowed to stand in the greenhouse, and the number of days that it took for seedlings to wither was recorded. With just sand or reddish loam soil, it took only 9 days for the rye grass to wither. In contrast, the perlite and soil mixes took 13 days to wither (a 44% improvement), and the grasses grown in 100% perlite took 28-32 days to wither!" (A 355% improvement) ("Effects of Horticultural Perlite on Lawn Growth" by Fumio Kitamura, Faculty of Agriculture, University of Toyko.)
(The picture above was taken after only 10 days with no water. On the right, the ryegrass grown in just sand and reddish loam soils had already wilted. Various mixes with perlite in the center did better, and grasses grown in 100% fine perlite on the left side of the picture did best.)
A test section was renovated by tilling turf grades of perlite into the top 6 inches of soil to create a 1:4 perlite to soil ratio. After two years of hard usage, the test section remains lush and green while the non-treated playing surface has turned brown with almost no grass remaining. And, although the frequency of irrigation is unchanged during the dry season, it has been determined that only one third as much water is required on the perlite treated sections.
Many years ago the St. Louis University High School renovated their over-used practice and playing fields with a one to three ratio of perlite to soil, and found perlite reduced ponding during heavy rains and helped prevent compaction. And according to the school's head football coach at the time, the school had far fewer injuries because of the softer playing surfaces.
Perlite Gradations---The Benefits of Finer Grades
Unfortunately, the perlite industry has made many mistakes in trying to market perlite to the turf grass and landscaping industries. Whereas coarser grades are good for professional peat mixes, finer grades are far better for use in preventing soil compaction and increasing water retention. And yet, there is seldom clear definitions as to what grades or types of perlite are being used for what kind of purposes. To alleviate this confusion, the internationally recognized Perlite Institute has established three distinct grades of horticultural perlite: fine, medium, and coarse. And whereas the traditional horticultural markets have used both the medium and coarse grades, all the applications of perlite mentioned in this article used the fine or unscreened medium grades---or what sometimes has been called Perl-Lome.
(For more information about perlite gradations, read our guide on Standard Gradations of Perlite---Fine, Medium, Coarse Defined.)
Similarly, perlite manufacturers often have experienced resistance to the use of perlite for water retention since so many areas of America had more than enough water, and irrigation was never a problem. Now with water usage an ever increasing concern in most parts of the country, and a constant concern of many western states, the use of finer grades of perlite to help retain water and prevent compaction is making more and more sense to many in the turf industry.
In fact, at its last annual meeting in San Francisco (May 1997), the Perlite Institute saw a presentation on the use of 100% perlite (fine grades) in large outdoor pots and huge commercial flower boxes in Israel. Essentially when compared to traditional peat-mixes, these new 100% perlite system seem to require far less water and care which is especially significant in the harsh growing conditions present in Israel. (For more information, read our guide on Using 100% Fine Perlite in Israel for Commercial Planters and Containers.)
For more information about these uses of perlite in both turf and landscaping applications, please contact:
To this day, perlite is used extensively throughout Japan in gardens, lawns, parks and golf courses in part because of this ability to retain water for a relatively low initial expense. At the Jawaharlal Nehru Stadium in Goa, India, the heavily used turf grass has to survive monsoon rains from June to September, but then virtually no rain from October through March. It also suffers from almost constant use. Both expensive and inexpensive amendments were tried with no success, and the playing surfaces were usually brown with large sections of no turf during the drier seasons.