Growing Coleus for Auxin Experiments: A Student's Guide

Coleus as a Houseplant? Not Ideal

Coleus (Coleus scutellarioides) are typically grown as outdoor annuals or in greenhouses. They require high light intensity—full sun or strong supplemental lighting—to maintain compact growth and vibrant color. In a typical home environment, even a bright windowsill rarely provides enough light, leading to leggy, weak plants.

Seedling Development Timeline

If you start from seed, two-week-old seedlings will generally be 2–4 inches tall. However, for a controlled auxin experiment, uniformity is critical. Consider purchasing young, vegetatively propagated plugs from a reputable greenhouse supplier to ensure consistent genetics and starting size.

Experimental Design Considerations

Your plan to remove growing tips and apply auxin pastes at varying concentrations (1×, 2×, 0.5×, 0.25×, 0×, and possibly 0.325×) mixed with talcum powder and water is a classic approach. However, the specifics—baseline height, tip length, and exact paste formulation—are highly dependent on the cultivar and growth conditions. These details are beyond general houseplant advice and fall into plant physiology research territory.

Recommended Resources

• Contact your local county extension office or university horticulture department for protocol guidance.
• Consult scientific literature on auxin transport and apical dominance in Coleus (e.g., papers on Coleus as a model for polar auxin transport).
• Consider using a growth chamber or light setup with consistent 14–16 hour photoperiods at 200–400 µmol·m⁻²·s⁻¹ PPFD.

Good luck with your science project! For general houseplant questions, I'm here to help.