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Many consumers assume that products on the store shelf must have been tested to prove their claims.  Certainly, fertilizers have to meet nutrient content requirements, and pesticides are rigorously tested for safety before EPA registration.

For some other garden products, however, no such testing is required before sale to the public.

A good example is vitamin B1 (thiamine), often sold to "prevent transplant shock" and "stimulate new root growth" when planting trees, shrubs, roses and other plants.  A study in the 1930's provided the basis for such claims.   Pea roots cut off from the plant were placed in a culture medium in the laboratory.

The researchers knew that thiamine was normally found in roots, so they put thiamine in the culture medium and found that root growth did occur.  Vitamin B1 is manufactured in plant leaves and sent to the roots, but if roots are cut off and placed in a petri plate, vitamin B1 stimulates growth of the roots when it saturates the culture medium.

Planting trees in a soil environment, however, is vastly different from a laboratory culture.  Most important, gardeners aren't in the habit of cutting off the root system when planting. Several studies using intact mums, apple trees, orange trees, pine, tomato, beans, pepper, corn, pear, watermelon and squash have failed to demonstrate that vitamin B1 treatments provide any type of growth response.

Some "root stimulator" products contain a rooting hormone and fertilizer along with vitamin B1.  These materials may increase rooting and growth, not the vitamin B1.

The bottom line: While root stimulator products are not necessary for transplant success, if you do use one, make sure it contains a rooting hormone and fertilizer rather than just vitamin B1. The vitamin B1 is for marketing purposes rather than actual effect.

BM