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Greenhouse Culture of Palms, (Continued Page 2)

Fertilizer, Injector Systems
 The greenhouse is the perfect place to utilize an injector system. It can be very cost and time effective. There are many commercial models available on the market. They are sized according to flow rates needed and do not need electricity to function. They utilize soluble fertilizer of any N/P/K ratio needed. A typical fertilizer might be an 18:6:18 or 18:6:12 ratio with microelements and blue indicator dyes. Follow your injectors directions. Even better, also measure the actual fertilizer concentration (parts per million of salt) coming out at the hose end. Electronic equipment on the market does this with ease. Also, check salt content in the soil once your fertilization program is in place. This is done with affordable equipment as well. Always observe plants for any evidence of salt burn. There is potential for unsightly salt buildup on the foliage if the solution is sprayed on the foliage.

One can also install a reverse osmosis system to improve water quality by removing municipal water salts.  Then, an injector system puts back in the desired fertilizer formulae.   

Fertilizer, Other Methods
If one cannot afford an actual injector system, there are inexpensive alternatives that utilize the venturi principal to siphon in fertilizer concentrate from a small basin directly into the hose. These devices are less accurate and drastically diminish flow rates when compared to actual injectors. They are, however, good for heavier liquid fertilizers such as fish emulsion. 

Organic and chemical fertilizers can also be used in the greenhouse. Bloodmeal is good for greening up leaves and carries little risk of burn. It is, however, odiferous. I have found that quick release fertilizers in the greenhouse have to be used very cautiously. Slow release fertilizers diminish risk of burn but are expensive and can still give erratic results. They are dependent on temperature or humidity for their release and this can vary in the greenhouse. 

reverse osmosis system
reverse osmosis system

 Palms are surprisingly pest free. However, any insect which can attack a palm can do so inside the greenhouse, except more voraciously. Infestations typically spread more rapidly in a greenhouse. The most common insect pathogens include aphids, scale, mealy bug and spider mites. When introducing new material into the greenhouse, make sure it is insect free to avoid new infestations. Preventative practices which can reduce problems include: spraying down the foliage, adequately spacing the plants, ensuring good air circulation and humidity, avoid overheating the greenhouse, removing dead leaves and debris, and treating problems as soon as they occur. For any given pest problem, it is best to consult your local nursery or garden center for the appropriate agent available in your locality. These vary from region to region and country to country. Always follow manufacturers instructions and use appropriate protective gear. Fungal problems are usually related to simultaneous cultural problems. Fungicidal agents must be given the same respect regarding human toxicity as insecticidal agents. Prophylactic use of fungicides as a soil drench on new seedlings is advocated by some growers. 

As palms grow faster in the greenhouse, more attention must be placed on pruning dead leaves. Always use clean equipment. Leaves are removed when they are unsightly and detract from the palms beauty. Do not remove healthy green leaves as these leaves are providing photosynthesis and nutrition for the plant. Allow old leaf bases to age such that they can be removed easily without scaring the trunk. Such scars can lead to infections with pink rot (Gliocladium Blight). Leaves should be cut on the lower petiole area as close to the trunk as possible. Cleaning of pruning equipment between plants will reduce transmission of various plant diseases. Do not allow leaf littler and trash to accumulate on the benches and pathways as this leads to fungal reservoirs. 

Weed Control
 It is imperative to control weeds on the ground and in the containers or they will overwhelm your greenhouse. One can purchase herbicides for some species of weeds. However, most growers hand weed and just keep up with it before the weeds have a chance to flower and seed. Plastic ground covers can be used on the pathways and under benches. Once established these covers remarkably diminish the amount of weeding needed and the need for herbicides. 

Repotting Palms
 Repotting of greenhouse container plants follows the same general guidelines as outdoor repotting with a few exceptions. Because of rapid greenhouse growth, it is quite easy for a plant to overgrow its container in a year or two. It does great in the greenhouse, but such a plant may then have too much leaf mass for the available roots and succumb on planting outdoors. Thus, repotting of greenhouse palms is a continual and important activity. To conserve money and utilizing rapid greenhouse growth, many commercial growers will pot a given plant into a container that may initially appear oversized for the plant, knowing that in a relatively short period this plant will grow into the larger container. If this is done, adjust watering patterns on these plants as less water is being consumed by the plant. If minimum greenhouse winter temperatures are maintained at 5 to 10 degrees centigrade or warmer, winter repotting can be done without fear. With lower temperatures, caution may be in order. 

repotting palm

Moving Plants Out of the Greenhouse
 Whether you are a grower or a customer purchasing plants from a greenhouse, acclimation outdoors is of critical importance. There are three things to consider when moving a plant out of the greenhouse: sunlight, temperature, and humidity. Of greatest risk is the outdoor sunlight. Your palm has typically seen less than full sunlight in the greenhouse. Higher humidity levels have also protected its foliage. The most common mistake is to take a sun loving species from the greenhouse and plant it directly into full sun. This invariably gives some degree of leaf burn. The plant actually looks scorched. This is most apparent on the leaves that are directly exposed to the sunlight, giving a faint or prominent brown discoloration to the green leaf. This can be avoided by gradually moving the plant into sun over a two to three month period. On first removing the palm, put it in shade. Every two to three weeks, progressively move it into a little more sun. If you see signs of burn, back down the gradient and acclimate more cautiously. Greenhouse plants can suffer sunburn any time during the year. Some species are more tolerant of this move, but caution is definitely in order. If a greenhouse plant is destined for filtered light, the acclimation process can be shorter. 

Cold burn can be avoided by not moving a plant out during cold weather. Unaccustomed cold can be just as devastating as sun. Make sure any threat of frost has passed. Cold frame greenhouse pose less risk than heated greenhouses. You can tell cold burn from sun burn in that the former is a more universal brown or faded look and will invariably hit the new leaf spear or newest tender foliage. The foliage will also look somewhat wilted and weak with time. Sun burn is on sun exposed areas only. Most growers have experienced cold damage while experimenting with new species of palms outdoors. Antidessicant sprays may aid with cold damage. Acclimation to less outdoor humidity may also lead to problems. Frequent spraying of the foliage with water and watching the soil for drying are in order. It is possible that a high humidity loving palm species may not survive in your area. However, reproducing a more moist microclimate in your garden may make the difference. Antidessicant sprays may likewise help with humidity problems. 


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