EFFECTIVE WATERING WITH HORTICULTURAL PERLITE

The Institute of Agricultural Research in Cypress recommends an 85% - 90% horticultural perlite, 10% - 15% spagnum peat

moss mix for rooting olive tree cuttings

Water shortages have become a major problem in many parts of the world. These shortages have affected virtually every phase of life and have created situations critical to life itself in many areas. Not the least affected by these water shortages are those engaged in the production of plant materials. Even in those areas where water is available, efficient use is the order of the day. In addition to the need for water conservation, irrigation costs have risen steeply. These factors impact dramatically on commercial growers worldwide.

Perlite's Unique Water Holding Ability

Horticultural perlite particles have a closed cell structure with a multiplicity of tiny crevices on their surface. These crevices trap water and hold it against drainage and evaporation, yet making it available to plant roots on-demand. As a result, available water does not drain away but the optimum  amount of water for plant growth is maintained where the roots need it to ensure optimum plant development. Particles of horticultural perlite will retain from three to ten times their weight in water. Water retention by horticultural perlite is not an indiscriminate action. The amount of water adsorbed on the surface of perlite particles is a function of the particle size distribution. Coarser perlite particles adsorb less water than finer particles. Thus, by adjusting the range of particle size employed, the amount of moisture retained can be carefully regulated to suit particular requirements. This enables the grower to prepare the optimum mix for each type plant being grown.

Stadium Turf in India

No grass is more highly stressed than stadium turf grass which is subjected to constant heavy traffic and compaction. Adding to this problem is irrigation, with water shortages or the lack of irrigation facilities creating an even greater barrier to maintenance of turf playing surfaces.  A case in point is the Jawaharlal Nehru Stadium in Goa , India . Grass management was dependent on limited irrigation October through March when there is no rainfall, intermittent showers in April and May and frequent rainfalls during the June to September monsoon season. In addition, the field was used almost daily for cricket, soccer, hockey and other athletic events. Because of this heavy usage, the field suffered from severe compaction and could not properly utilize available water. A test section of the stadium was renovated by tilling horticultural perlite into the top 6 inches (150 mm) of soil to create  a 1:4 perlite to soil ratio and then reseeded. After two years of hard usage, the test section remains lush and green while the non-treated playing surface has brown areas and sections with no turf cover. In addition, the perlite treated section shows no evidence of compaction and is a more desirable playing surface. Excess water during the monsoon season rapidly drains away while an optimum amount of water is retained during the dry season. Although the frequency of irrigation is unchanged during the dry season, it has been determined that only 1/3 as much water is required on the perlite treated sections.  

ROLE OF PERLITE IN HYDROPONIC CULTURE

By  Dr. David A. Hall

Principal

Pershore College of Horticulture

United Kingdom

H orticultural perlite has a long and enviable record of performance as a propagating and growing medium throughout the world. It has been successfully used in virtually all horticultural applications including glass-house growing, landscaping, lawn and stadium turf and in a variety of container applications. Time and time again it has proven its superiority in meeting the needs of commercial growers and home gardeners. Hydroponic culture is no exception. Extensive testing over a period of years has documented the superiority of perlite over other methods of hydroponic culture. For example, tomato crops hydroponically grown in perlite have produced yields 7% higher than crops grown in rockwool. In addition to significantly increased yields, perlite culture is particularly easy to manage and offers additional benefits.

"...TOMATO CROPS HYDROPONICALLY GROWN IN PERLITE, HAVE PRODUCED YIELDS 7% HIGHER THAN CROPS GROWN IN ROCKWOOL."

Watering

As a rooting medium, perlite is superior to rockwool. The outstanding feature of perlite is then ease with which a constant supply of water and nutrients can be maintained in the substrate simply by placing the plant container in a shallow reservoir of nutrient solution. Perlite's strong capillary attraction for water automatically draws up solution from the reservoir at the same rate that water is removed by the plants. Nutrient enriched water is trapped in the tiny irregularities on the surface pf perlite particles where it is available for use by plant roots. Excess solution remains in the reservoir. The ease with which an optimum moisture level can be maintained around roots is the key to perlite's success and it is a significant advantage over rockwool which has less capillarity.

Rockwool is close to being waterlogged at its maximum water-holding capacity, when it can hold as much as 85% water by volume and, hence, too little air for optimum root development and growth. Perlite's free-draining nature means that it retains less than half this amount of  water. Roots in perlite are always well aerated and well watered.

In contrast to perlite, the moisture content of rockwool fluctuates from too wet (just after watering) to too dry (just before watering). To minimize such fluctuations, growers using rockwool must resort to a 'little-and-often' watering routine. Nutrient solution may have to be added to rockwool slabs as often as 24 times per day.

Fertilizer and Water Costs

To avoid the possibility of waterlogging when rockwool is used, polyethylene sleeves of rockwool slabs should be slit to drain out excess nutrient solution. This continual waste of water and fertilizers can increase the combined cost of these items to more than double that for perlite culture where a reservoir system can be easily adapted.

Re-Use

Perlite is physically stable and, unlike rockwool, will retain its excellent air/water balance for many years if handled carefully. Some growers have used perlite for tomatoes more than one growing season and it has subsequently been re-used for potting mixes and soil conditioning. If perlite is reused, sterilization may be necessary.

Summary

Horticultural perlite provides more constant moisture status around the roots at all times irrespective of weather or stage of root growth.

Perlite ensures more even watering throughout the growing area.

There is less likelihood of over-watering with horticultural perlite.

Perlite culture avoids wastage of water and nutrients. The use of perlite eliminates the need to grade growing floors accurately. 

INDOOR GARDENING WITH PERLITE

T he green revolution has led to the introduction of hundreds of unheard-of plants and has resulted in new life for old favorites. One reason why people grow plants indoors is their ease of culture. In days past, plant lovers would go into the garden and scoop up some soil which they would mix with rotted manure or other compost and use it to pot their plants. Fortunately they can now rely on modern growing mixes containing perlite, sphagnum peatmoss and other components. These mixes are readily available at garden centers, some hardware and department stores.

Perlite is a volcanic material that, when heated to 1600 deg.F (850 deg.C) makes an excellent ingredient for house plant growing mixes. Perlite particles create tiny air tunnels, which allow moisture and oxygen to flow freely to roots. This is important since 98% of all oxygen a plant gets is absorbed through its roots. Poorly drained growing mixes shut out oxygen; root "pumps" shut down and the plant dies from suffocation.

Over-watering is the cause of perhaps one half the cases of plant failure. Perlite in a growing mix serves as a "life guard", not only promoting good drainage but allowing precious oxygen to flow to roots. Perlite makes moisture, oxygen and nutrients readily available to plants. Because of the unique shape of each particle, plus its permanency, moisture and nutrients can cling to the crevices until the plant needs them, while the granular quality provides quick drainage of excess moisture and allows space for oxygen - vital for healthy plant growth. Commercial growers as well as home gardeners can buy perlite mixes or make their own. Equal parts of perlite and sphagnum peatmoss and sand (or rotted compost or loam) makes a fine growing mix while equal parts of sphagnum peat moss and perlite make an excellent seed starter.

"COMMERCIAL GROWERS AND HOME GARDENERS HAVE FOUND THAT PERLITE IS THE

IDEAL ROOTING MEDIUM..."

Perlite for Increasing Humidity around Plants

Since the average home is extremely dry when the heating system is operating, plant foliage often takes on a scorched look on tips and edges. One way to overcome this is to set trays of water in the plant area and add perlite. Set the plants on the perlite which should be kept moist. Water is slowly released into the atmosphere, benefiting the plants.

Perlite Reflects Light

Cloudy winter days often result in poor houseplant or seedling growth. Light coming in a window can be greatly increased by placing perlite in the bottom of plant trays and on the surface of the growing mix where light rays will be reflected back up to plants. This can make the difference between spindly plants and good stocky growth. The same applies if plants are being grown under fluorescent lights. Just be sure perlite is kept moist so you can take advantage of the extra humidity.

Watering Plants

Frequency of watering depends on the type of plant and size. Most plants prefer the growing media to be "just moist" at all times. Some plants, like Jade plant and large-leaved Ficus like the growing media to become almost dry before water is applied. Care should be taken however, to see that the growing media does not become so dry as to cause dropping of leaves or shrinking of the soil ball to the point at which a space forms between it and the pot. When this happens, water rushes down the inside of the pot rather than wetting the root zone. If this happens, or if leaves drop because of lack of water, set the pot in a large pan of tepid water until the whole root ball is moistened. The plant will respond, usually within half an hour. Plastic pots hold moisture longer than unglazed pots, which have pores for air to pass through. Since the soilless mixes contain much lightweight material, you can usually tell by lifting the pot whether or not the mix has dried out completely. With large pots, you can push a wooden dowel probe (like a pencil) into the pot. If it comes out moist you know there is still some moisture left.

Perlite for Starting Seeds

Fine perlite can be used alone as a seed-starting medium or it can be mixed half and half with shredded sphagnum moss or shredded peat moss. Many seeds have limited "pushing-up" power. Perlite alone or perlite mixes are ideal for seed starting because they are light in weight. Moisten the medium thoroughly, then sow the seeds on top. Very fine seeds can be atomized and left to settle into crevices. Be sure the medium does not dry out. This can be prevented by keeping the seed box sub irrigated at all times, until seeds sprout. A plastic cover over the box helps maintain humidity. Other seeds can be covered with a light dusting of perlite and sphagnum peat moss. Another requirement for good seed germination is a constant temperature (for most seeds) of 72 deg. F (22 deg.C). Water for sub-irrigation can be put directly in the planting tray or a plastic liner can be shaped to hold water. Place the seed boxes in this liner and keep water in it.

"PERLITE ALONE OR PERLITE MIXES ARE IDEAL FOR SEED STARTING..."

Another use for perlite in seed starting is to give better distribution of fine seeds. Take a clean salt shaker and place about 1/4 inch (6mm) of very fine perlite (perlite may be poured into a sieve and the fine particles shaken out) in the salt shaker. Pour the packet of seeds on top, replace the cap and shake to mix in the seeds with the perlite. Sprinkle the mixture evenly over the perlite/ peat moss seedbed.

Perlite for Rooting Cuttings

Both commercial growers and home gardeners have found that perlite is the ideal rooting medium for cuttings from ordinary houseplants or from woody shrubs, evergreens or vines. It is important to keep the perlite moist at all times and to keep cuttings out of direct sun. If temperatures are cool, rooting is hastened by applying bottom heat. Misting on warm days helps the cuttings retain moisture and hastens rooting. Home gardeners can use a terrarium as a rooting chamber, whereas commercial growers would use a greenhouse, coldframe or hotbed. 

ROOF GARDENS THAT ARE GENTLE ON THE ROOF

The current, eco-friendly trend of designing commercial buildings with rooftop gardens has put a premium on the use of expanded, volcanic perlite in making lightweight soils for these structures. Regular, wetted soil can tip the scales at well over 100 pounds a cubic foot – while a perlite/peat moss mixture will weigh a mere 40 pounds while providing the long acknowledged advantages of superior air porosity and water-holding capacity for plants. Rising fuel costs have also forced nurserymen to acknowledge the lightweight advantages of perlite-based soil mixes when shipping plants across the country. All signs are for continued growth in this valuable industrial mineral.

THE SYSTEM

Horticultural perlite and peat moss mixtures are used by professional growers for many reasons. They form a lightweight planting mix for rooftop gardens and other areas where normal soil use presents a weight problem. 

ADVANTAGES

• Lightweight - Horticultural perlite and peat moss, fully watered, weigh only 40

lbs. per cubic foot. Soil fully watered weighs 100 to 125 lbs. You can reduce planter weight at least 60% by specifying horticultural perlite and peat moss as a growing mix.

• Long-Lasting Economy –  Horticultural perlite is an expanded volcanic mineral. Unlike organic matter, perlite will not deteriorate.

• Retains Water and Plant Food -  Horticultural perlite will retain three to four times its weight in water and will not become soggy. At the same time, it increases the nutrient and air-holding capacity of the planting mix.

• Chemically Inert - Horticultural perlite has an essentially neutral pH and will not noticeably change the alkalinity or acidity of a planting mix.

• Completely Sterile – Horticultural perlite is sterile (having been “expanded” at 1800 ° F.), free of insects, diseases, weed seed and other soil-borne pests and can be used without steam sterilization or chemical treatment of any kind.

• Safe, Easy to Use - Horticultural perlite is clean, odorless, easy to handle and free of all additives or materials toxic to plant growth. 

DESIGN FACTORS

Planters – whether individual pots or large beds – should have adequate drainage to sewer systems or roof decks. A sleeve of 1/8” galvanized hardware cloth around a roof-type drain is recommended to keep the drain and piping clear. Also recommended are layers of gravel and horticultural perlite on the bottom of planter to promote drainage.

The planters themselves can be constructed of reinforced concrete. To further reduce weight, use of perlite aggregate concrete will reduce planter weight at least 75%. Pre-formed fiberglass planters may also be used to save weight. Recommended planter depths are indicated in diagram at bottom of sheet. 

APPLICATION

Suggested mix for nurserymen who prefer some soil in their planter mix, the following proportions have been suggested for one cubic yard:

• 1/3 cubic yard horticultural perlite

• 1/3 cubic yard coarse peat moss

• 1/3 cubic yard clean soil plus nutrients

Subsequent feeding may be with each watering or at two-week intervals.

Planters and containers with 100% perlite or with very high percentages of perlite are