Rooting Hormone for Cannabis Clones: Does It Help?
Rooting hormone may help cannabis clones, but NC State notes it is not always necessary. In a Canadian study, cuttings dipped in a 0.2% IBA gel rooted at a 2.1 times higher rate than cuttings given a willow extract gel, with 1.6 times better root quality. How the leaves were handled mattered too.
What Is Rooting Hormone?
The rooting hormone tested on cannabis by Caplan and colleagues was a gel containing 0.2% indole-3-butyric acid, or IBA. They compared it with a gel made from 0.2% willow (Salix alba) extract (Caplan et al. 2018). NC State’s propagation chapter tells gardeners to dust rooting hormone on the wound when air layering, then adds that rooting hormone is not always necessary (NC State). It also notes that herbaceous cuttings, such as coleus and chrysanthemum, root at a high rate and do so quickly.
Does Rooting Hormone Help Cannabis Cuttings?
Caplan’s team kept cannabis cuttings in a growth chamber for twelve days and then scored rooting success and root quality. The IBA gel gave a 2.1 times higher rooting success rate and 1.6 times higher root quality than the willow extract gel (Caplan et al. 2018). The abstract compares the two gels with each other, so it does not show how either one compares with no hormone at all. The authors conclude that the IBA product they tested is preferable to the willow-based one.
Source: Caplan et al. 2018, cannabis stem cuttings after 12 days in a growth chamber. The study compared the two gels with each other, not with untreated cuttings.
Data for this chart:
| Treatment | Result relative to willow extract gel |
|---|---|
| Willow extract gel (0.2%) | 1.0 |
| IBA gel (0.2%), rooting success | 2.1 times higher |
| IBA gel (0.2%), root quality | 1.6 times higher |
Source: Caplan et al. 2018, cannabis stem cuttings. Root quality did not change with leaf tip removal.
Data for this chart:
| Leaf treatment | Rooting success |
|---|---|
| Leaf tips left whole | 71% |
| A third of each leaf tip removed | 53% |
Gel, Powder or Liquid: What Is the Difference?
Neither source compares gels, powders and liquids. The cannabis study tested gels only, and NC State describes dusting a powder onto a wound for air layering (NC State). Whatever you use, follow the directions for that product. Read the product label first, and check the rules where you grow.
How Do Growers Apply Rooting Hormone?
The same study found that removing a third of each leaf tip cut rooting success from 71% to 53%, and cuttings with three leaves had 15% higher root quality than those with two. Cutting position on the stock plant had little effect. The authors advise at least three fully expanded, uncut leaves (Caplan et al. 2018). Dipping the cut end and placing it straight into a moist medium is grower practice. For the full process, see our guide to making cannabis clones, and for humidity while roots form, our post on building a clone box. A growing supplies list helps you gather the rest.
No mother plant to take cuttings from yet? You can start with our cannabis seeds.
Sources
- Caplan et al. 2018, Canadian Journal of Plant Science: Vegetative Propagation of Cannabis by Stem Cuttings
- NC State Extension Gardener Handbook: Propagation
Here, Kind Seed Co sums up the research above as general growing information for cloning.
FAQ
What is IBA?
IBA stands for indole-3-butyric acid. It was the active ingredient in the rooting gel that Caplan and colleagues tested on cannabis stem cuttings, at a 0.2% concentration. In their trial, the IBA gel gave a 2.1 times higher rooting success rate than a willow extract gel and 1.6 times better root quality.
Does willow extract work as well as IBA?
Not in the cannabis study cited here. Caplan and colleagues found the 0.2% IBA gel gave 2.1 times higher rooting success and 1.6 times higher root quality than a 0.2% willow extract gel after twelve days. They concluded the tested IBA product was preferable to the willow-based one.
Should you trim leaf tips on cannabis cuttings?
The cannabis study suggests not. Removing a third of each leaf tip lowered rooting success from 71% to 53%, while root quality stayed about the same. The authors recommend cuttings with at least three fully expanded, uncut leaves, whether the cutting comes from the top or the bottom of the plant.
How many leaves should a cannabis cutting keep?
Caplan and colleagues found that cuttings with three leaves had 15% higher root quality than cuttings with two, although leaf number did not change the rooting success rate. Their advice is to keep at least three fully expanded, uncut leaves on each cutting, from either apical or basal positions.
