Growing Orchids in Perlite

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Growing Orchids in Perlite
Original Report by: Dr. Wally Thomas and Barb Thomas
Charles Island Gardens
West Vancouver, CANADA

Odontioda SEA NYMPH 'Island Rainbow', H.C.C. A.O.S, hydroponically grown in 100% perlite.

This Plant Guide summarizes 5 years of outstanding success in growing orchids at Charles Island Gardens using the perlite reservoir technique with intermediate size perlite. This method, by which all major genera of orchids can be grown, allows for a constant supply of nutrient to the plant by taking advantage of the unique capillary action of perlite. An outstanding characteristic of this method of culture is that one cannot over water and that there is always excellent aeration. Table 1 compares the excellent properties of perlile with those of other commonly used growing media.

Additionally, perlite is a naturally occuring material. Horticultural perlite (about 1/8 inch, 3 mm in diameter) is pretreated by pouring perlite into a tub of water and fertilizer solution. The perlite is pushed into the water several times and the floating perlite is skimmed off. This wet perlite is a wonderfully easy material with which to pot. Such pretreated perlite shows no evidence of compaction after three years.

TABLE 1 - COMPARATIVE PROPERTIES OF GROWING MEDIA COMMONLY USED WITH ORCHIDS
	BARK	PEAT	ROCKWOOL	PERLITE
Ph of Medium Fertilizer Control Leaching Aeration Disposal Health Hazard Sterility Management Simplicity Weeding Availability Cost Ease of Potting Repotting Time Nutrient Overwatering Rewetting Cation Exchange Buffering	Slightly Acid Good Easy Good Easy Care No Fairly Easy Fair Fairly Easy Good Varies Good 1-2 Years Minimum Yes Fair Yes Slight	Acid Good Fair Fair Easy Care No Fairly Easy Fair Fairly Easy Very Good Varies Good 1-2 Years Minimum Yes Fair Yes Acid	Slightly Alk. Good Fair Fair Problem Care Yes Fairly Easy Fair Fairly Easy Fair Varies Good 1-2 Years Nil Yes Poor No No	Neutral Very Good Very Easy Very Good Easy Care Yes Very Easy Very Easy Very Easy Very Good Competitive Very Good 2 Years+ Nil No Easy No No

Potting and Repotting

Ordinary pots may be converted for reservoir use by inserting a cup in the bottom. Specific reservoir pots and saucerless hanging baskets are excellent. To plant a 10 inch (25 cm) sauce rless basket, the basket is filled to 2 inches (5 cm) from the top with perlite. Thirty to forty seedlings are planted and the surface covered with pea gravel. To ease the transition, cling wrap material is wrapped around the hanging wires leaving an opening at the top. The plants are bottom watered for the first six weeks, after which time the wrap is removed and the plants treated normally. Mature plants are best repotted when new growth has just started. Plants are set a little deeper than with other media and pea gravel is used to hold the plant firmly in place as well as to decrease evaporation. Repotting is only required when space for new growth is needed. There is no plant setback when repotting from perlite to perlite.

Bed Growing

Eight inch (20 cm) deep beds are constructed of wood, lined with 6 mil. black polyethylene with an overflow outlet at 1-1/2 inches (4 cms) from the bottom to provide a reservoir. Overflow solution is collected for recycling.

Watering/Fertilizer

Pots should be heavily watered before they dry. One cannot overwater with the perlite system. Charles Island Gardens has experienced no disease in 5 years and the system offers the potential for simple and inexpensive automation. A complete hydroponic fertilizer suitable for most orchids is shown in Table 2.

TABLE 2 - CHEMICAL COMPOSITION OF FERTILIZER SOLUTION
N P K Ca Mg SO⁴	49 ppm 18 ppm 76 ppm 42 ppm 14 ppm 18 ppm	Fe Cu Mo Zn Mn B	0.37 ppm 0.0035 ppm 0.05 ppm 0.11 ppm 0.33 ppm 0.10 ppm
These levels may be achieved by using, by weight, one part Ca(NO₃)₂ to 2 parts 7-11-27 (Plant Prod^) or 2 parts 5-11-26 (Peters^†), diluted according to your proportioner to yield an E.C. of 600 ľmhos. 7-9-5 (Dyna-Gro^††) at an E.C. of 600, although low in calcium and magnesium, provides satisfactory growth. For most orchids, the final diluted fertilizer solutions should have a pH of 5.8 to 6.4. ^ Registered trademark of Plant Products Co., Ltd. ^† Registered trademark of W.R. Grace Co., Ltd. ^†† Registered trademark of Dyna-Gro Corporation

Photos
Odm. crispum 'Island Shirley'

Information given herein is from sources considered reliable, but no guarantee of accuracy can be made or liability assumed. Your supplier may be able to provide you with more precise data. Certain compositions or processes involving perlite may be the subject of patents.
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