Excerpt from Jorge’s Upcoming Book:
The Cannabis Encyclopedia: Indoor, Outdoor and Greenhouse Cultivation, Concentrates and Cooking Medical Marijuana
Chapter 7: Clones and Cloning
Preparing to Clone
Cloning is the most traumatic incident cannabis plants can experience, aside from harvest. Clones go through an incredible transformation when they change from a severed green growing tip to a rooted plant. Their entire chemistry changes; the stem that once grew leaves must now grow roots in order to survive. Clones are at their most fragile point in life just after being cut.
Big, healthy growth like this makes excellent clones.
While rooting, clones require a minimum of nitrogen but increased levels of phosphorus to promote root growth. Sprays should be avoided during rooting, as they compound cloning stress. Given good instruction and a little experience, most gardeners achieve a consistent, 100 percent clone survival rate.
All of these stems were cut on an angle so that more interior stem surface is exposed. This is where many roots will grow.
Large cuttings having large stems packed with starch will grow roots more slowly than small clones with small stems will. The excess starch in moist substrate also attracts diseases. Thin-stemmed clones have fewer reserves (accumulated starch), but they only need enough reserve energy to initiate root growth.
Small clones with a few leaves need less moisture and will root faster than big cuttings with many leaves. At first leaves contain moisture, but after a few days the stem is no longer able to supply enough moisture to the leaves, and the clone suffers stress. A small amount of leaf space is all that is necessary for photosynthesis to supply enough energy for root growth.
These little clones were just taken and still need to get used to the new environment. When they grow roots, they will look much stronger.
Integrity in Parents
1. Maintain 18-to-24-hour day photo period
2. Keep plants healthy
3. Grow for 6 to 12 months
4. Report as needed
Average Root Growth in Cannabis Clone
Cell division starts
First root nubs form
Roots start to grow
Enough roots to transplant
This chart shows average times for roots to grow from the stem.
Note: Clones taken from younger growth root faster than those taken from older growth.
Look for plants that dawn small (rootlet) nubs (primordia) near the base of the trunk. Such plants tend to strike roots exceptionally fast.
Most ‘Skunk’ and indica varieties grow roots easily.
Ruderalis crossed with indica or sativa varieties are autoflowering and do not make suitable mother plants.
Outdoor varieties with a slight tendency to pre-sex (designate sex) in an 18-hour photoperiod include: ‘Early Girl’, ‘Early Skunk’, and many others. Check with seed companies for details. But early flowering does not exclude them as mother plants.
Clones taken from weak, leggy mother plants most often produce weak, leggy clones. Harvested plants that have been induced back into vegetative growth can also produce weak clones if not fully reverted.
Clones root well within a slightly acidic pH range of 5.5 to 6.6. Aeroponic clone gardens normally do best with a pH of 5.4 to 5.6. Most diseases grow poorly below these pH levels. Always make sure there is plenty of air in the rooting medium to stimulate root growth.
Do not kill clones with kindness and fertilizer. At best, giving clones an excess dose of fertilizer causes rooting to be delayed. In fact, a dose of ammonium nitrate, a common salt-based fertilizer, will actually stop root hairs from growing.
Inexperienced gardeners and diseased plants cause most clone-rooting problems. Weak plants that lack vigor provide slow-rooting, weak clones. Poor growing conditions also affect the strength of clones.
See “Dipping Clones in Miticide” in Chapter 7, Clones and Cloning. Watch out for dips that coat leaves too heavily. The dip should cover well enough to protect plants with insecticidal and fungal properties, yet allow stomata to breathe.
Clean room: leaves on the floor are cleaned away three to four times daily.
If a spider mite infestation occurs, many gardeners destroy infested clones and start over with clean clones. Others spray with aerosol pyrethrum or another organic miticide. Remember, all pesticides—natural or not—are phytotoxic. Spraying cuttings is a bad idea in general, including antidesiccant sprays. Sprays clog stomata and can impair root growth in clones. If you must use sprays, use natural organic sprays, apply them when it is cool, and keep their use to a minimum. See “Spraying” chapter 24, Pests and Diseases.
Transplant clones before they become rootbound!
The roots on this clone are circling the container and the roots near the center are already turning dark, signifying overwatering and pending death. Do not over water clones. Keep the medium evenly moist but do not let it get soggy. Any kind of stress disrupts plants and slows rapid growth. Different mediums need distinct watering schedules. Rockwool holds water for a long time, while peat pellets need watering more often. Clones are tender;they have a small developing root system and need extra vigilance now.
Richard Lee, Oaksterdam University, inspects clones in a spotless clone room.
Keep the cloning area clean. Do not take clones where fungus spores and diseases are hiding! Pythium flourishes in high temperatures and excessive moisture. Powdery mildews prefer cool moist conditions. Spider mites, whiteflies, and thrips love weak, tender clones. Remove infested clones from the cloning room. Cooler, humid conditions, 65°F to 78°F (18°C–25°C), inhibit most mite reproduction and avert infestations. But cool, humid conditions may increase chances of specific fungal attacks.
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