Auxins

• Auxins are chemicals that act as growth-regulating hormones. Plants produce their own auxins to elongate stems, form new leaves and develop roots. Horticulturists apply synthetic auxins to plants to accomplish the same goals. Early work with auxins in the 1930s included additions of B1 to synthetic auxin compounds. In 1949, after successful root growth in treated plants, the prevailing theory suggested that B1 was the primary contributor. Later researchers, including Chalker-Scott, debunked that theory with repeated scientific literature refutations reporting that B1 acting alone could not stimulate root growth.
  
  

Root Stimulators

• Some gardeners propagating plants from stem cuttings use products labeled as root stimulators or rooting hormone powders. Vitamin B1 is listed on some labels, along with naphthylacetic acid, NAA, and indole butyric acid, or IBA. These ingredients help stems form roots more quickly compared to untreated stems, but excessive applications are harmful and can burn stems. For seedlings with established roots, these ingredients suppress crown growth and tend to be toxic to primary root development in order to stimulate lateral root growth.
  
  

Micropropagation

• Mircopropagation, or tissue-culture propagation, is the clonal increase of new plants in test tubes. Vitamin B1 is a component of tissue-culture agar media that encourages growth response of new plants. These plants, however, start at the cellular tissue level and have unformed stems and roots. In this application, B1 is favorably indicated; however, this indication does not apply equally to already formed plants. Skalau's research reports that vitamin manufacturers base their claims for successful root growth using B1 on tissue culture research, not research on whole plants.
  
  

Self-Manufactured Vitamins

• Healthy plants make their own vitamins, with help from healthy soil. Soil fungi and bacteria work synergistically with plants by producing other vitamins that are available to plants through their root systems. Additional human vitamin supplements are unnecessary and, in many cases, harmful to plants. Claims to the contrary without substantive scientific research are baseless. Excessive amounts of vitamins, which plants need only in trace amounts, can interfere with the normal, healthy biological function of plant systems. Chalker-Scott advises against adding any unessential and potentially toxic chemicals, including those that are organically based.