Perlite - How useful it can be in your Gardening Job!

Seed Germination
Perlite speeds up germination and improves seedling growth.   

For seeds, sow on a well-watered mixture of equal parts perlite and Sphagnum Moss Peat. Alternatively, add 1 part perlite to 2 parts ready-mixed potting compost. 

For use pure, keep wet at all times by capillary irrigation or intermittent mist.  After sowing, sprinkle seeds with a thin layer of fine peat and cover with glass or plastic to retain moisture until germination, then feed

Potting Mixes
Perlite is used in potting compost mixes to improves aeration, draining and insulation.  Perlite can be used to open up the structure of ready-mixed loam or peat-based composts.

For soilless compost mixtures, use 3 or 4 parts of Sphagnum Moss Peat to 1 part of perlite (80/20).

For loam-based compost mixtures, use equal parts 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.

Rooting and Cuttings
Perlite speeds uprooting, reduces the 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 growth disruption from transplanting.

For soft stem and leaf cuttings, use a mixture of equal parts perlite and Sphagnum Moss Peat (50/50).   For harder cuttings and fragile plants, increase the proportion of perlite up to 4 parts perlite to 1 part peat (80/20).

For mist irrigation, perlite may be used 100% where sterility is essential. Keep well-watered but ensure free drainage. Feed plants as soon as roots develop.

Soil Conditioning
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. These improvements will last for many years. 

For difficult seedbeds and flower beds, use up to 25% perlite worked into the top 5-10cm before sowing. 

For trees, shrubs and roses, mix perlite with the soil when backfilling the planting hole to stimulate root growth.  

Turf Dressing
Because Perlite improves aeration and drainage, it will assist the air-moisture balance and ensure better root development and turf growth. Golf course greens treated with perlite will show improved resilience and greater tolerance in use under extreme weather conditions - wet or dry.

For compacted and poorly drained areas on old turf and for the establishment of new turf, use as follows: Spike over the affected area with a hollow tine then spread a thin layer (2-5mm) of damp perlite pre-mixed with a suitable fertiliser.  Rake or brush evenly, and water thoroughly.  Note: a 100-litre bag of perlite will give on average a 2mm layer over 50sqm.

Capillary Watering, NFT & Hydroponics
Perlite is an inert, sterile, neutral, ultra-lightweight aggregate with a very high air and water-holding capacity.  To sterilise perlite for re-use, steam, flame-gun or treat with any proprietary chemical steriliser.   

For capillary watering use, allow at least 25mm (1 inch) depth of perlite in place of sand or gravel in polythene-lined benches or suitable trays.  

For ring culture and low-cost commercial production of tomatoes, use perlite in polythene lined trench or channel, and saturate with nutrient solution. 

Special Note:  
With electrical heating cables use a 50/50 mix of perlite and sand to prevent overheating.