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Jorge’s Cannabis Encyclopedia: Ensure Female Seedlings

*Henk, owner of Dutch Passion Seeds, was kind enough to allow us to adapt this information about environmental factors from his archives. Above Photo: These strong seedlings are receiving 14 hours of light and 10 hours of darkness to promote more female plants.

How to Help Ensure Female Seedlings

Ethylene diluted in water and sprayed on cannabis plants increases the number of female flowers and decreases the number of male flowers. To have the fullest effect, the hormone must be applied before pre-flowers appear. At this point plants are in the process of designating their sex, male or female.

These strong seedlings are receiving 14 hours of light and 10 hours of darkness to promote more female plants.

Ripening fruit (especially bananas) releases a lot of ethylene. Several bunches of bananas can be set in a small, enclosed garden room containing the plants.

Large quantities of ethylene can be generated through the use of a catalytic generator, available here.

The spray releases a gaseous vapor of ethylene. Ethylene gas surrounds and overwhelms plants with the female hormone, promoting female tendencies. When enveloped in female hormone, cannabis plants designate sex and soon start producing female hormones, female pre-flowers, and, later, female flowers. See chapter 22, Additives, for more information on the hormone ethylene.

Note: Some of the products that release ethylene are plant growth regulators (PGRs). See chapter 22, Additives. Note 2: Ethylene sprays can be phytotoxic when not diluted properly or when they are applied in hot weather.

Increase Yields Treat seeds with carbon dioxide (CO2) or ethylene before sowing to strengthen and increase root development, growth, budding, flowering, ripening, seed production, and overall yield.


When a seed sprouts, its white taproot emerges. Soon afterward the sprout breaks through the soil surface and a pair of cotyledons, also known as seed or seedling leaves, appears. The seed leaves spread out as the stem elon- gates. Within a few days, the first true leaves appear, and the little plant is now officially a seedling. This growth stage lasts for 3 to 6 weeks. During seedling growth, a root system grows rapidly, while green, aboveground growth is slow. Water and heat are critical at this point of development. The new, fragile root system is very small and requires a small but constant supply of water and warmth. Too much water will drown roots, often leading to root rot and damping-off. Lack of water will cause the infant root system to dry up.

As seedlings mature, some will grow fast and strong and appear healthy in general. A little soil heat now will help nurture small seedlings to a solid start. Other seeds will sprout slowly and be weak and leggy. Cull sickly plants, and focus attention on the remaining strong survivors. Seedlings should be big enough to thin out by the third to fifth week of growth. Thinning out seedlings is often very difficult for gardeners who pay exorbitant prices for a few seeds!

Seedlings need at least 14 hours of light daily. They require less-intense light now and grow well under fluorescent tubes for the first 3 to 4 weeks. CFL or HID light can also be used. Com pact fluorescents should be 12 to 18 inches (30–45 cm) and the HID 3 to 4 feet (90–120 cm) above seedlings for best growth.

If not growing in rich organic soil or pre-fertilized mix, start feeding 2 to 4 weeks after seeds have sprouted. Some gardeners wait until leaves yellow to begin feeding. Use a mild quarter- strength solution.

Strong, rapid seedling growth is essential for strong, healthy plants and a bountiful harvest. Take special care to nurture seedlings so they get a good start on life. Any lack or excess of water, light, or temperature will stunt seedlings. Avoid high temperatures and low light levels, which cause lanky growth. The first 3 weeks of life for auto-flowering and auto-flowering feminized varieties are critical. These varieties grow for 70–80 days from seed. Without super strong growth during the first 21 days, yields are much lower.

The seedling stage is over after 3 to 4 weeks of growth. At this point rapid foliage and root growth starts. Rapid growth aboveground is the most obvious signal that the vegetative growth stage is in process. Plants need more room to grow; transplanting into a larger container is essential to hasten development.

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