CANNA Rhizotonic is a root stimulator that growers normally pour into the root zone with the watering. Some growers also spray it on the leaves. This article explains when a leaf spray makes sense, how to mix and apply it, and when you should not spray at all.
The most useful moments for a leaf spray are three: right after transplanting, the first weeks of vegetative growth, and recovery after a shock such as heat or overwatering.
What CANNA Rhizotonic is
Rhizotonic is a root stimulator based on an extract of the seaweed Ascophyllum nodosum. CANNA says it also contains organic compounds, vitamins and minerals, but it does not name the vitamins or give amounts.
CANNA describes the product as supporting three things:
- root development
- the plant’s resistance to stress
- recovery after transplanting
Products of this kind are often called biostimulants (products that help the plant grow and cope with stress, rather than feeding it main nutrients). The forum explains the idea in What is a Biostimulant?.
Translator’s note: before you buy, ask an authorized distributor in Thailand whether the bottle sold here is registered with the Department of Agriculture (กรมวิชาการเกษตร) and carries a Thai label. A registered product with a Thai label is also what a GACP auditor will expect to see in your input records.
Why spray it on the leaves
A leaf spray (foliar spray) puts the solution straight onto the leaf surface. Part of it enters through the stomata, the tiny breathing pores on the leaf. The original article says this route bypasses the roots entirely.
Translator’s note: “bypasses the roots entirely” overstates it. Some of the spray always runs off into the pot, and leaves absorb only part of what lands on them. A fair way to put it: a leaf spray reaches the plant even when the roots are working poorly. It does not replace root feeding. CANNA itself says Rhizotonic can be used as a foliar spray.
This route is useful in four situations:
- Roots are damaged or still small. This covers fresh cuttings and newly transplanted plants. See Mother Plants and Cloning, Part 2 for cuttings and Transplanting Cannabis for transplant shock.
- The plant is under stress. Examples are heat, overwatering, or nutrient lockout (nutrients are in the medium, but the roots cannot take them up). See Nutrient Lockout in Cannabis.
- You want faster early vegetative growth.
- The plant looks weak and needs support to recover.
What to do: spray only when one of these four situations applies. The purpose is to help weak roots or a stressed plant, not to add a routine extra step.
How to mix and spray
Dose. Use the foliar rate printed on the current CANNA label or product information. The original article gives no number of its own, and this rewrite does not add one. CANNA’s product information gives no separate foliar rate. It lists only rates for the nutrient solution: 40 ml per 10 litres as a first dose and when re-potting, 20 ml per 10 litres in vegetative growth, and 5 ml per 10 litres in flowering.
Translator’s note: if the label gives only a root rate, do not guess a leaf rate. Ask an authorized distributor in Thailand or CANNA’s technical support. Then test it on two or three plants first, and check the leaves the next day for burnt spots or edges.
Steps:
- Mix with clean water adjusted to pH 5.8–6.2. Clean water does not leave deposits on the leaf. The pH range matches what the plant handles well. See pH and EC for Cannabis.
- Use a sprayer with a fine mist. Fine droplets cover the leaf evenly. Big drops run off or sit on the leaf as puddles.
- Spray the undersides of the leaves. Most stomata sit on the underside, so more of the solution can enter there.
- Spray when the lights are off, or in early morning or late evening. The original article gives this to avoid light burn, when strong light hits wet leaves.
- Do not spray in flowering. Use the spray in the vegetative phase and for cuttings only.
How often: 1–3 times per week, during the first 1–2 weeks after transplanting, or when stress symptoms appear.
Translator’s note on timing: the original says both “always spray when lights are off” and “early morning or late evening”. These fit together if you read them as one rule: spray when there is no strong light on the leaves. In Thailand, add a second rule: the leaves should dry within a few hours. Warm, humid nights keep leaves wet for a long time, and wet leaves in the dark help mould. Indoors, spray shortly before lights-off and keep the fans running. Outdoors or in a greenhouse, early morning usually dries faster than late evening in the rainy season.
What to do: write down the date, the dose from the label and the plants you sprayed. After 1–2 weeks, compare them with plants you did not spray. That tells you whether the spray is worth the work in your room.
Practical tips
- No strong light on wet leaves. Spray in darkness or weak light so the leaves are not burnt.
- Use it on the leaves and at the roots together. The original article says combining both gives the best result. The leaf spray helps while the roots are weak, and the root application builds new roots.
- It works with all CANNA nutrient lines. The original names Terra, Coco, Aqua and Hydro. See the CANNA Fertilizer Guide for what each line is for.
- Storage. Keep the bottle closed in a dark, frost-free place (CANNA’s wording); cooler is better. Use a diluted solution within 24 hours, and throw away what is left.
Translator’s note: a “cool place” is hard to find in a Thai storeroom at 30–35 °C. Keep the bottle off the floor, away from the roof and walls in the sun, and out of the grow room. An air-conditioned room is best. Mix only the amount you will spray that day, so nothing needs to be stored diluted.
When not to spray
- During flowering. Moisture on the buds raises the risk of mould, such as bud rot. See Botrytis (Gray Mold).
- Under intense HPS or LED lighting. HPS means high-pressure sodium lamps. Wet leaves under strong light can burn.
- When room humidity is already above 70%. Extra water on the leaves pushes humidity higher and keeps leaves wet longer. See Grow Room Climate Control.
Translator’s note: in the Thai rainy season, outdoor and greenhouse humidity is often above 70% for much of the day. In those weeks, the rule above means you should mostly not spray. Use Rhizotonic at the roots instead. If you grow indoors, check a hygrometer (a humidity meter) before every spray. If a power cut stops the fans or dehumidifier, do not spray until they run again.
What to do: hang a hygrometer at plant height. Spray only when it reads below 70% and the plants are still in vegetative growth or are cuttings.
Your questions
Have you sprayed Rhizotonic on cuttings or after transplanting in Thai heat? Post your dose, timing and results below this topic, so other growers can compare.
References
- CANNA, product information and label for CANNA Rhizotonic (current edition) — for the foliar rate and product description.