All plants naturally possess hormones, including the growth hormone auxin, which is produced in immature parts of the plant, where growth is necessary. Synthetic auxins are used in hormone rooting powders and gels to replicate natural growth conditions in plants, and encourage roots to form. Hormone rooting powders often also contain cytokinins (another plant growth hormone), fungicides and other chemicals, which reduce the risk of the plants succumbing to fungal infections.
Rooting hormones increase the chance of your cuttings taking root. What's more, the root will usually develop quickly and be stronger than when plant-rooting hormones aren't used. While many plants root freely on their own (see below), using a root hormone makes the task of propagating 'difficult' plants much easier.
However, rooting hormones are rarely essential. While many gardeners swear by them, others don't think it's necessary.
Fins out when and how to use rooting hormones, below.
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When to use rooting hormones
As a general rule, the time of year can help you decide whether or not to use rooting hormones. Typically, low concentrations of rooting hormones are used for herbaceous softwood cuttings, which are taken in summer and root quickly, and high concentrations are used for woody hardwood cuttings, which are taken in winter and take longer to develop roots.
However, some plants root more easily than others. The following plants rarely 'strike' (take root) without hormones:
Fuchsias, salvias and snapdragon also benefit from a little extra help.
When not to use rooting hormones
If you're an organic gardener, you may not want to use synthetic rooting hormones as they're artificially made and contain fungicides. Fungicides have been linked to bee declines and, if used incorrectly, can inhibit photosynthesis, so may not aid strong growth in the long term.
What's more, some plants simply don't need them. These include:
That said, there are organic rooting powders available – these contain naturally occurring auxins, so do seek out these products if avoiding synthetic chemicals is important for you.
How to use rooting hormones
Rooting hormones come in three forms — powder, gel and liquid. It's best to use powders and gels as it's possible to damage the cuttings if you accidentally use too much of the rooting liquid.
Ensure your cuttings are fresh and the wound is clean. Cut just below a node or leaf join, where there are already naturally occurring plant auxins, then remove any lower leaves, where the roots will grow from.
Pour the powder or gel into a sterile container and then simply dip the base of your cutting into it, and tap or shake the cutting to remove any excess (if the powder won't stick then dip the cutting in water, first). Stick the cutting into a pre-made hole in moist potting compost, preferably around the edge of the pot, where soil evaporation is at its lowest.
Cuttings are vulnerable because they don't have roots to absorb moisture. Prevent evaporation from the leaves by creating a humid environment, either by placing the cuttings in a propagator or fixing a clear plastic bag around the pot to lock moisture in. A heated propagator will also provide bottom heat, which can aid root growth.
Place your cuttings in a spot where they will receive dappled sunlight.
Keep an eye out for new leaves. Once new growth is apparent, roots will have developed. Remove the plastic bag, or propagator lid, and water the compost if necessary.
Tips for success
- Take your cuttings in the morning when they're full of water
- Avoid taking cuttings from flowering shoots, as these are less likely to root
- Remember that applying too much rooting hormone can damage the cutting
- Don’t get the rooting hormone on the foliage, because this causes misshapen leaves
- Cut large leaves in half to reduce the surface area from which the cuttings can lose moisture
- Use bottom heat to also aid root growth – you can buy heated mats or heated propagators to create an even, warm, temperature from below