From the report “Humic Acid Seed and Substrate Treatments Promote Seedling Root Development“, of Jack A. Hartwigsen and Michael R. Evans, published at Hortscience
Seed of Pelargonium ×hortorum L.H. Bailey ‘Freckles’ (geranium) and Tagetes patula L. ‘Bonanza’ (marigold) were soaked for 12, 24, or 48 h in solutions containing:
- + 0 (deionized water),
- + 5000, 10,000, or 15,000 mg/L humic acid (HA)
- + 5000, 10,000, or 15,000 mg/L nutrient controls (NC) containing similar levels of nutrients prior to planting.
Soaking in deionized water (DI) and NC treatments had no significant effect on root fresh weight. However, several of the HA treatments increased root fresh weight of marigold seedlings, and all increased geranium root fresh weight.
+ deionized water, + 2500 mg/L humic acid (HA), + 2500 mg/L nutrient control (NC), + 5000 mg/L HA, + 5000 mg/L NC.
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