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9 Reasons for a custom soil mix

May 12, 2010

9 Reasons for a custom soil mix
One of our customers in Florida posed the question,

"I wonder why growers use heavy (weight-wise) potting mixes. You grow quality plants in this soil but doesn't it add to your shipping cost?"

A thought provoking question. Why do we use relatively heavy, mineral based soil for plants we ship? First a little background - then the nine reasons.

Our general purpose potting soil

In over 50 years of horticultural endeavors, I have used countless soils for nursery, florist and production containers. Bagged soils, bagged soils with my own custom additions, made-from-scratch soils, stock bulk mixes, 100% organic matter mixes, mineral based formulas, ad infinitum.

During this time, I have narrowed the list of potting mixes down to three: seed starting mix, general purpose mix, and house plant soil. Of course, for very special uses - starting Restio or Protea seed, rooting Begonias or for the various genera of orchids there are highly specialized mixes. But for the vast majority of our uses, there are just these basic three. Virtually everything we ship is in the GP (general purpose) mix.

This soil mix is comprised of ground bark and sawdust from our local forest products industry, volcanic pumice rock and rock dust from a local quarry, and two different sands - also from local quarries. To this we add a complex assemblage of fertilizers, rock dusts and soil inoculants. It quickly "blooms", heating up and rapidly changing as the various microorganisms colonize the media. Within a few weeks, it is ready for us to use. The vast majority of what we grow is planted into the general purpose mix as soon as possible; seedlings, cuttings and divisions.

But . . . and this is a big "but" . . . it is heavy. And heavy translates to small but tangible increases in shipping charges.

Here are the 9 reasons we use this "heavy" soil:

1. All of the ingredients are locally produced. This is both an issue of being sustainable and a function of transportation costs. No other material that we have tried is locally sourced or as inexpensive to truck.

2. This soil has proved to be satisfactory for a very wide range of plants. Virtually everything we grow outside of the obvious exceptions like orchids thrive in this mix.

3. The water retention characteristics and CEC (cation exchange capacity) of this mix fits our growing regimen.

4. It is heavy enough to help keep the plants upright in the wind of coastal California. This is a very important issue for us!

5. It has a long life, allowing us to use it for plants like Helleborus and Brunnera that require more than one year to become salable plants.

6. It works well in pots large to small, and in both plastic and clay containers.

7. In the hopefully rare case of a plant going bone dry, it re-wets with ease.

8. It has a long shelf life. This greatly simplifies our inventory process.

9. It is a certified organic material.

I intend to keep working on this issue over time. Saving weight on our shipments is a good thing in many ways, as the customer and the environment all benefit. I hope now you all can understand why we use the soil we do.


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Plants mentioned in this article