The art of cloning plants could be the most useful of all ‘indoor’ techniques. Cloning allows growers to make the most of every female plant and it’s a skill that anyone can master with a little practice.
Outdoor growers who clone their plants are able to identify gender early in the season and multiply their female plants during the long vegetation period. With low-powered artificial lighting, a promising female can even be preserved for next year’s outdoor crop.
Due to its common association with indoor growing and hydroponics, cloning might appear to be a complex process. In fact, nothing could be further from the truth.
Just as hemp seedlings will take advantage of the smallest chance to grow, cuttings will quickly make roots and become healthy small plants if a few conditions are met.
Good cuttings are made from strong, green stalks, preferably the growing shoots of the stem and branches.
If possible, cuttings should be 10-20cm long and a few millimetres thick. Avoid stems that are turning woody or hollow, as these are less likely to root. If the aim is to produce a few strong cuttings from each plant, growers should select 12cm sections of the healthiest top shoots. Larger cuttings have more energy and have a better chance of surviving.
If the aim is to make as many clones as possible, any 5-10cm piece of green stem with a growing shoot and a leaf or two can be used. A 30cm branch can be cut at each internode, making 3-6 clones. Tiny cuttings can also turn into clones, though they may take too long to grow to a decent size after rooting. Nevertheless, pieces of stem 3cm long and 1mm thick can root with vigour in bright, humid conditions.
Before planting, treat cuttings with rooting hormone in powder or gel form.
While a good soak in rooting solution is enough to get many clones started, a final treatment with a rooting aid that clings to their stems will increase success rates.
With a razor blade, make a diagonal cut to remove the last millimetres of stem, then dip the cutting in hormone powder/gel. To encourage rooting, many growers gently scrape the lower stems before dipping. A disposable safety razor is a good way to remove a couple of ultra-thin slices from the stalk.
Place treated cuttings in a moist, airy medium that holds them firmly – expanding peat tablets, a 50/50 mix of soil and perlite, cocoa-fibre or rockwool, if available. Clones have no problem rooting in a small rockwool block, then being transferred to soil.
After planting, outdoor clones are given the natural light cycle. Some growers shade rooting clones during the hottest part of the day, while others adopt a ‘survival of the fittest’ attitude. Viable clones will appreciate direct sunlight, and should root quickly.
In hot, dry climates, rooting clones may require a transparent covering to retain humidity. Keep the clones’ medium moist, but not saturated. In good conditions, clones should root in 10-20 days.
Cloning for Sex
The first clone taken from a plant can reveal the parent’s gender with 100% accuracy. It’s easy to reduce the light cycle of cuttings – allow them 12 hours of daylight, then cover them or move them to a dark area. This is much simpler than covering a single branch of a large plant to reveal gender.
When seed-plants reach 30cm, they can yield a cutting or two, which can be given a 12/12 light cycle immediately upon being planted. They will show their gender in 10-14 days, and in many cases they’ll root as well.
It’s fine if these first clones don’t become healthy small plants. Their purpose is to reveal the gender of the parent early in the season, allowing males to be eliminated and all subsequent cuttings to be taken from female plants.
As an added bonus, cloning for sex causes seed-plants to be ‘topped’ early in the season, leaving plenty of time to regenerate a strong double-stem.
Cloning to Multiply
Outdoor growers with plenty of space may clip plants to train them into huge bushes, while balcony growers often cut plants solely to restrict their size.
In both situations, cloning allows extra plants to be made from foliage that is normally discarded.
To keep a balcony plant around 1m by the end of flowering might require quite a lot of pruning. Instead of throwing away over 50% of a female plant during the growing phase, the removed foliage can be made into dozens of copies that plant, all of which will finish under the required height.
Growers who prune plants to make them large and bushy can produce huge numbers of clones. Branches are clipped at regular intervals throughout the vegetative phase to encourage them to split and grow in two directions. As plants increase their size and number of branches, each pruning will yield more cuttings than the last. While this might eventually produce more cuttings than most growers could use, remember that a rooted female clone makes a lovely gift.
Indoors, cuttings are almost always taken while plants are in the growing stage, as the aim is to preserve a plant in its vegetative state. Outdoors, it is even possible to take clones during the initial weeks of flowering, when the first single flowers begin to show. Cuttings from plants that have begun to flower will often root more quickly than normal clones and should continue blooming at the same rate as the parents.
This means that even in the final, pre-flower trimming (where lower and inner branches with little budding potential are clipped), outdoor growers can clone any viable pieces of stem that are removed from plants.
Every green section of stem with a healthy internode can become a small plant when treated with kindness. Six branches cut from a medium-sized plant in July or August could be turned into 10, 20 or 30 cuttings. Even with a low survival rate of 20%, the result can be a few bonsai flowering plants.
If you’re growing outdoor plants this year and you’ve never made clones, you could try the following experiment just to see how easy it is to produce them, even if you have no particular need to multiply your harvest.