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BOTANICAL CONSERVATORY REFERENCE

- FERTILITY

Fertilization Programs

Fertilization programs for most interior plantings should be designed for plant health maintenance, not necessarily for fast growth. High nitrogen levels can cause unwanted overgrowth, resulting in minor element deficiencies, weak tissue, and the need for frequent pruning and replanting. Salt build-up in the soil can cause drought-like symptoms and root damage. The resulting growth is prone to disease and pest problems.

If care is taken in soil design - to insure pH and elemental balance - fertilizer applications can be kept to a minimum. This is increasingly important as water resources become more threatened and the environmental impact of chemical usage become more critical.

Fertilizer Types

Water-soluble commercial fertilizers are the most popular fertilizers among those gardens surveyed. These fertilizers are available in a wide variety of N-P-K ratios with many containing trace elements as well. Most include a dye to help in monitoring the function of injector systems. Formulas are available without dye for applications where dye would not be desirable. Some suppliers offer custom formulations for larger orders.

Due to their high solubility, these premixed fertilizers can be injected using single-head systems at the very high ratios needed for periodic fertilizer applications. Feed tank ratios below 200 ppm do not require constant agitation to remain dissolved, making it convenient for constant feed programs.

This form of fertilizer is also ideal for foliar feeding with special formulas available for this purpose. Foliar feeding is sometimes used to help correct deficiencies caused by soil problems.

Some conservatories supplement liquid feed with additional nutrients tailored to plant requirements (eg. Mg, Mn, and K for palms) while others rely on visual signs of deficiency to indicate the need for supplemental elements. Visual diagnosis alone is not an advisable practice as some deficiencies cause permanent damage and/or take extensive chemical applications to correct.

Soil salt levels should be monitored when using water soluble chemical fertilizers.

Organic fertilizers such as fish emulsion, manures, and composts were the second most popular fertilizers in the survey. Organics are used more with delicate plants such as ferns, and in sensitive environments such as zoos, or bird and butterfly houses. Organics tend to release their nutrients more slowly and last longer than the water-soluble chemical fertilizers. The popularity of organic fertilizers is growing as environmental concerns increase and more dependable sources for these products become available.

Bone meal is high in phosphorus (usually 15 to 25%) which is available over a long period of time. It should be used carefully in situations where high pH is a problem because of a high lime content. A better source of phosphorus for soils of medium pH might be phosphate rock. Although it contains calcium, it is generally not leached into the soil.

Super phosphate is a similar product, but with more readily available phosphorus for correcting existing deficiencies.

Cottonseed meal is a good organic source for nitrogen (6-8%) and to a lesser degree, potassium (2-3%). Cottonseed meal can also help acidify soils. It should be dug into or incorporated into the soil.

Fish emulsion is a very mild organic fertilizers. It is difficult to use with high concentrate injectors such as Anderson's because of the density of the product. Intake screens can easily clog and an agitator should be used for concentrations higher than the 1:15 ratio used with hose siphon injectors. Even with constant agitation, problems occur at ratios as low as 1:100.

Those who have used fish emulsions for a couple of decades know how bad it once smelled. Later products have been deodorized somewhat, but the residual smell after the product has been used indoors is still a factor to be considered. Aside from these problems, fish emulsion remains a popular organic fertilizer, especially for ferns, epiphytes, and bonsai.

Animal manures are used by some conservatories for fertilizer as well as a soil conditioner. The same caveats apply as when using manures as an amendment (see discussion under SOILS section on Compost). Animal manures should be aged, leached, or composted to temper the nitrogen content. Poultry is the highest in nitrogen followed by horse manure, then cattle. They work best when dug into or incorporated in soil mixes.

In some areas, commercially prepared products are available from cattle lots and poultry houses. These have been composted, if not pasteurized, and have a somewhat reliable analysis. Manure products also include pelletized fertilizer and the fertilizer tablets or cakes so popular in bonsai culture.

In many cases, liquid feed and slow release fertilizer are supplemented with organics.

As in water-soluble fertilizers, soil salt levels should be monitored.

Slow release fertilizers are similar to the water-soluble in formulations, but are coated with a material that allows slow release of the nutrients in response to moisture and temperature. They are available in pellets, tablets, and stakes in a variety of formulas and release periods. Most recently, fertilizer has been combined with water gels and made into stakes and disks. These disks are pressed into the soil around the plants and absorb soil moisture. The moisture and fertilizer are then available to the plant roots as needed.

Granular fertilizer is sometimes used as a topdress in existing plantings, but usually mixed into new mixes before installation. They are useful for replacing nitrogen lost in the breakdown of organic material Most formulas release their nutrients quickly. Some, like sulfur coated urea, are coated for slower release, although they are still faster than the slow release fertilizers discussed above.

Special purpose fertilizers are formulated for specific plant types such as palm fertilizer or tropical foliage feed. They contain a balance of nutrients and trace elements known to be necessary for a specific crop. Surprisingly few conservatories use these specialty mixes.

Chelated micronutrients are trace elements needed for plant nutrition that have been treated with a chelating agent. This is a process that keeps the micronutrients available to the plants through foliar feeding or root feeding. This is very useful for conservatories with soil pH problems or nutrient imbalances that cause the nutrients in the soil to become 'locked up' and unavailable to the plant roots.

The most commonly used chelates are iron, magnesium, and zinc. Combination formulations are available in soluble mixes and coated forms such as the "fritted" trace element mixes.

Mineral supplements. Greensand or galuconite greensand, the only purely mineral product mentioned in the surveys, is harvested from undersea deposits. It contains 5-6% potassium that is slowly released over a long period of time. It also contains a variety of trace elements, including 15-20% magnesium.

Fertilizer Scheduling

Constant feed applications are less prevalent than periodic applications with very few conservatories relying on testing for feeding regimens. Constant feed programs for permanent plantings should be monitored by soil testing on a regular basis as the potential for an imbalance or over fertilization is greatly increased.

Soil Testing

A regular fertilizer application program is not a guarantee against nutritional deficiencies. The availability of a nutritional element to a plant is dependent on the presence and level of other elements as well as factors such as soil pH. For example, if calcium levels become too high, potassium and many minor elements become unavailable to the plants roots. If the pH is not correct, no fertilizer program can be effective.

Testing is the most dependable, if not the most convenient, determination of nutritional equilibrium. Periodic, in-house testing with a simple soil test kit can be supplemented with semi-annual testing by the extension service or a private laboratory.

Keep in mind that nutrient levels that might be interpreted by testing as normal for general agriculture may be insufficient or imbalanced for tropicals. Using palms as an example, magnesium, manganese, and potassium requirements are much higher than for most other plants. And, in the case of palms, deficiencies in these nutrients cause severe damage that is very difficult to correct.

A good plant nutrition program should be based on soil tests and adjusted to the particular requirements of the plants being grown.

Individual Programs

Of those gardens surveyed, almost all use fertilizer programs customized to individual plant types (i.e.: orchids, cactus, palms). Most of these programs share a basic design as shown in the summaries that follow:

Palms: specialty fertilizers and coated slow release formulas
Average ratio: 3:1:3
Rates: 100-150 ppm constant, 300-450 ppm periodic
Supplements: KNO3, MgSO4, Mn, and iron chelates
Deficiencies: magnesium, potassium and iron; problems with pH

Note: This is a tendency toward high nitrogen levels that might need to be re-evaluated. Although increased nitrogen is used to help palms outgrow previous damage, an increase in insect problems, especially scale insects, has been recorded. Less nitrogen may also minimize other nutrient deficiencies.

Tropicals: liquid feeds of water soluble formulas
Average ratio: 3:1:2
Rates: 100-150 ppm constant, 200-450 ppm periodic
Supplements: MgSO4, iron chelates, trace mixes
Deficiencies: magnesium, iron; problems with overgrowth

Note: See note under Palms.

Succulents & Cactus: specialty fertilizers (low N), water solubles
Average ratio: 2:1:2 or 1:1:1
Rates: 150 ppm constant, 3200 ppm periodic. Most seasonally
Supplements: fish emulsion monthly
Deficiencies: none reported

Note: Organic content and pH of root zone sometimes overlooked.

Orchids: water soluble (high N). fish emulsion monthly
Average ratio: 3:1:1 or 2:1:1
Rates: 100-150 ppm constant, 100-400 ppm periodic
Supplements: KNO3, MgSO4, Mn, and Iron chelates
Deficiencies: nitrogen, iron, micronutrients; problems with pH.

Notes: Although water treatment, such as reverse osmosis, is very beneficial to orchid culture, fertilizer should be increased to compensate for increased leaching.

Ferns water soluble, fish emulsion
Average ratio: 2:1:2 or 2:1:1
Rates: no constant feed reported, 50-200 ppm periodic
Supplements: MgSO4, iron chelates
Deficiencies: magnesium, potassium and iron; problems with pH

Note: High nitrogen fertilizers can easily burn sensitive fern species. Watch for salt build-ups.

Bromeliads: water soluble (high N) no dye, fish emulsion
Average ratio: 3:1:2
Rates: 150 ppm constant, 200-400 ppm periodic
Supplements: none reported
Deficiencies: none reported

Note: Some feed only organic fertilizer in cups. Avoid salt build-up in cups.

Aquatics: slow release tablets, fruit tree spikes

Rates: medium N beginning of season, high P mid-season
Supplements: KNO3, MgSO4, Mn, and iron chelates.
Deficiencies: nitrogen, phosphorus.

Notes: Care should be taken to keep fertilizer contained and out of the water to prevent algae problems.

This is a part of the first chapter of the Botanical Conservatories Compendium. Other planned chapters include conservatory climate control, management, mission, staffing, biological pest control, support facilities, budget planning, construction considerations, etc. This will be available through American Association of Botanical Gardens & Arboreta resource center, or email Don Pylant.