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Tuesday, June 12 2012
The eternal question for palm and cycad growers is, “What is the best soil mix for my cycads and/or palms?”  I have concluded that there is no one mix that is perfect for any one group of plants.  More realistically there are many different mixes that have provided growers with modest to very good success.  After all if the mix is terrible, then the grower would not be a grower for very long.  Each grower that has had a measure of success may often wonder if he/she could improve the soil mix by adding this or that or by altering the percentage of this or that.  So success is often achieved by fine tuning several basic ingredients.

The purpose for developing a soil mix formula ultimately is to optimize the growth potential of the plant by providing the best environment for the plant’s root development.  Just as a sound foundation is essential to building a skyscraper, a healthy root system is an absolute requirement to growing a healthy plant.

It is not the purpose of this article to give growers a given soil mix formula.  I think it is more important to give general guidelines that can help each grower to understand and formulate a mix that will be suitable to his/her particular location and plant material.

Nearly all palms and cycads require soil that drains well.  Excessive water retention in the soil mix can rot the root system and lead to the eventual death of the palm or cycad in most cases. 

In order to provide good drainage, most soil mixes are primarily comprised of 1) sand, pumice, decomposed granite, and small gravel; and in order to provide food for the plant, soil mixes also are also comprised of 2) organic material which includes leaf mulch, compost, bark chips, etc.  The intangible but vital ingredient that is difficult to quantify is the array of micro-organisms that are present in all viable productive soil.  These micro-organisms break down and convert mulch and other organic materials into a useful form that can be consumed by our plants.

A plant’s native habitat can help determine the type of soil conditions that will best promote its growth.  For example, Encephalartos from the southern 20% of the African continent, further from the equator, experience climatic seasonal changes similar to the southernmost states in the continental U.S.  Most of those species experience dryer and cooler seasonal periods than the central African species, closer to the equator, which receive overall warmer temperatures and seasonal monsoonal rains.  So those species from the south, further from the equator, can tolerate cooler, dryer conditions, and have adjusted to well draining soil to best resemble their native conditions.  Conversely the central African plants from close to the equator can tolerate a heavier percentage of organics in their soil, because they come from a hotter wetter climate.  That additional organic material will more closely match the native soils of the central African species.

For all percentages hereafter, the first percentage number shall refer to inorganics, and the second percentage number shall refer to organics.  As for making an appropriate soil mix, a good starting point would be a 50% combination of sand, pumice, d.g., and/or small gravel, and a 50% combination of mulch, compost, peat moss, bark chips, etc.  These two groupings of material can be modified by altering the percentage from a 50%/50% mix to as much as 33% inorganic to 66% organic for plants native to wetter regions.  This mix affords greater water retention, while still maintaining a good degree of drainage, which most palms and cycads need.  Conversely for plants that favor a dryer soil mix, something like a 65% inorganic to 35% organic proportion would be appropriate.  This will help to facilitate good drainage in the root zone.  In addition these plants will likely benefit from more frequent watering as seasonal conditions dry out, because their soil dries out more rapidly.  For most cycads, where excessive dry conditions persist, a seasonal (once a year) top dressing of mulch over the root zone helps to keep the soil and roots from drying out too rapidly, and it nourishes the beneficial micro-organisms that feed the roots.

In conclusion, the percentages of sandy to organic all can vary.  I have presented just a general guideline that will help the grower who needs a place to start.  Again, I would prefer to empower the grower with the ability to reason and understand the needs of the plants, and then to formulate and refine a soil mix that meets those needs.  A grower may even choose to have several different formulas, to accommodate the needs of different species of plants, which may hail from different native habitats.  And, of course, a grower many need to rework his/her percentages if it is clear from the garden that plants’ particular needs aren’t being met.  It’s a little like cooking.  If it doesn’t taste quite right, adjust the ingredients.

Grow and prosper, Keith

Posted by: Keith Huber AT 03:00 pm   |  Permalink   |  Email

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