What is Perlite and how and why is it used in the garden?
What is Perlite?
Perlite is a generic term for a naturally occurring siliceous rock. The distinguishing feature that sets perlite apart from other volcanic glasses is that when heated to a suitable point in its softening range, it expands from four to twenty times its original volume. This is due to the rapid expansion of water within perlite, which creates the extremely light perlite that we use within the garden arena, with many benefits when it comes to it's horticultural uses..
Perlite is mined and expanded all over the world. The United States is estimated to be the largest consumer and producer of crude and expanded perlite. However, other leading countries producing perlite include China, Greece, Japan, Mexico, Hungary, Armenia, Italy and Japan.
Uses of Perlite
Perlite's many uses and beneficial properties include:
¤ Inorganic, inert and sterile.
¤ No known toxicity or fire hazard.
¤ Prevents compaction - improves aeration and drainage.
¤ Does not decompose - lasts for years.
¤ Stimulates root initiation and vigorous growth.
¤ Insulates and minimises temperature fluctuations.
¤ Almost neutral pH.
¤ Holds moisture but does not become soggy.
¤ Free from disease, weeds and insects.
Perlite encourages quicker germination, improved seedling growth and less check when pricking-out or potting on.
Sow on a well watered mixture of equal parts of perlite and Sphagnum Moss Peat or add 1 part perlite to 2 parts of ready-mixed potting compost.
Perlite may also be used 100% - provided that it is kept wet at all times by capillary irrigation or intermittent mist. Sprinkle fine peat over the seeds, and cover with glass or plastic to retain moisture until the seeds have germinated, and then feed.
Perlite is used wholly or partly in place or sand or grit in potting compost where it improves aeration, draining and insulation, and also facilitates re-wetting. Perlite can be used to open up ready-mixed loam or peat-based composts.
For soil-less composts mix 3 or 4 parts of Sphagnum Moss Peat with 1 part of perlite (80/20).
For loam based compost mix equal parts of sterilised loam, peat and perlite (1:1:1) plus limestone and nutrients. Alternatively a 1:2:1 mix may be used. Mix thoroughly, then water well after planting, and feed as appropriate.
Perlite speeds up rooting, reduces risk of damping off, provides an optimum balance of air and water, and makes water logging almost impossible. It also minimises damage to roots and check to growth during transplanting.
For soft stem and leaf cuttings use a mixture of equal parts perlite and Sphagnum Moss Peat (50/50).
For harder cuttings, and for fragile plants increase the proportion of perlite up to 4 parts perlite to 1 part peat (80/20). Under mist irrigation perlite may be used 100% where sterility is essential.
Keep well watered but ensure free drainage. Plants should be fed as soon as roots develop
Perlite improves the texture of heavy silt or clay soils by increasing aeration and drainage. It also minimises the tendency to 'cap' over germinating seeds, and lasts for many years.
Treat difficult seed beds and flower beds by working up to 25% of perlite into the top 5-10cm before sowing.
For trees, shrubs and roses, mix perlite with the soil when back-filling the planting hole, in order to stimulate root growth. Firm the mixture around the roots and water thoroughly.
Perlite improves aeration and drainage in compacted and poorly drained areas on old turf and also helps the establishment of new turf. Perlite will greatly assist the air-moisture balance and ensure better root development and turf growth. Greens will show improved resilience and greater tolerance in use under extreme weather conditions - wet or dry.
Use a hollow tine spike all over the affected area, then spread a thin layer (2-5mm) of damp perlite pre-mixed with a suitable fertilizer. Rake or brush evenly, and water thoroughly. Note: a 100 litre bag of perlite will give on average a 2mm layer over 50 sq.m.
Capillary Watering, NFT & Hydroponics
Perlite is an inert, sterile, neutral, ultra lightweight aggregate with a very high air and water-holding capacity. Perlite can be sterilised for re-use by steaming, by flame-gun or by treating with any proprietry chemical sterilizer.
For capillary watering use at least 25mm (1 inch) depth of perlite in place of sand or gravel in polythene-lined benches or suitable trays.
Special Note: With electrical heating cables use a 50/50 mix of perlite and sand to prevent overheating.
For ring culture and low cost commercial production of tomatoes use perlite in a polythene lined trench or channel, and saturate with nutrient solution.
See Perlite in our Store.