In November 1998 we introduced our "Female Cannabis Seed". We did this after our own experiments showed that from female seed, we acquired almost 100% female off-spring.
In the meantime we are six months further on . We have received a lot of feed-back from our customers. The reactions are mostly positive, clients who have successfully produced almost 100% female off-spring. However there have been reactions from customers who found a few hermaphrodites or males plants. Apparently environmental influences affect the sex of the female seeds as well. Because of the fact that Female seeds do not grow into female plants under all circumstances, we changed the name from "Female Cannabis Seeds" into "Feminised Cannabis Seeds".
From literature and from our own findings it appears that the growth of a male or a female plant from seed, except for the predisposition in the gender chromosomes, also depends on various environmental factors. Not only the origination of entirely male or female plants is partly affected by these environmental factors, the number of male and female flowers on a hermaphrodite plant is affected as well. The environmental factors that influence the sex of the plant (or the flower in the case of hermaphrodites), are among other things:
The quantity of nitrogen and potassium of the seedbed.
Humidity and moistness of the seedbed.
Level of temperatures.
Colour of the light used.
Length of daylight.
Stress, any form of stress, makes that more male individuals will originate from seed. Even the taking of cuttings from female plants may produce male or hermaphrodite cuttings.
To optimise the result, changes in one or more of the above-mentioned environmental factors for a certain period during growth, may be applied. During this time these environmental factors will deviate from the standard growing system for maximum harvest and quality, as described in nursery literature. The desired change(s) in the environmental factor(s) are started from the moment that the seedling has three pairs of real leaves (not counting the seed-lobes). This is the moment that male and/or female predisposition in florescence is being formed. After approximately two weeks the standard growing system can be reconverted to.
Of the 5 above-mentioned environmental factors the first three are the most practical:
1. Level of nitrogen and potassium of the seedbed: A heightening of the standard level of nitrogen makes for more female plants originating from the seeds. A lowering of the nitrogen level shows more male plants. A heightening of the level of potassium tends to show more male plants, while a lowering of the potassium level shows more female plants. A combination of a higher nitrogen level for the period of a week or two and a lowering of the potassium level is recommended.
2. Humidity and moistness of the seedbed: a higher humidity makes for an increase in the number of female plants from seed, a lowering for an increase in male plants. The same is valid for the moistness of the seedbed.
3. Level of temperatures: lower temperatures make for a larger number of female plants, higher temperatures for more male plants.
4. Colour of light: more blue light makes for female plants from seed, more red light makes for more male plants.
5. Hours of daylight: few hours of daylight (e.g. 14 hours) makes for more female individuals, a long day (e.g. 18 hours) makes for more male plants. *
Now let me just make a few adjustments here to this. You can do whatever you want to your plants in seedling stage and early vegetative stage of growth and it will not effect your final male to female ratios. The time when things should be near perfect is in or around the 3rd to 4th week of vegetative growth. This is the CRITICAL TIME for getting those female ratios up and up. I realized this clearly when noticing how some plants hermed because of problems that occurred around this period of the plants development. If the problems occurred before this time - no herms. So for this reason I surmised that this is when the crucial gender selection is made by the plant. Now I believe that the genders are set in the seed however the environment has a massive impact on how this is expressed in the final phenotypic expression of the plants gender. There are probably many genes that govern this, however lets get into how to up these female ratios.
At the 3rd to 4th week of vegetative growth make sure that your plants are free from stress. No pests attacks, no fungi attacks, no mold, no irregular photoperiod, not underwatered, not overwatered, not pruned or topped, a cannabis friendly soil mix, not recently transplanted, no small pots. If have these basic growing conditions under control then we can move onto the real forces of female production from standard seeds.
N:K and nutrients. What this simply boils down to is that you have the right nutrients present in the right ratios. A nutrient formulation that has roughly equal parts N, P and K is great but if the P levels go up or the N levels go down you are starting to look at a flowering type food for cannabis. If you do this then your odds of producing mostly females is greatly decreased. Make sure that you get those N, P and K levels to almost run from higher to lower amounts from N to P and K. I have noticed that equal portions of N to P an K can help with the female ratios but the higher N is certainly more helpful. So around the 3rd of 4th week of growth make sure that the ratios are good and that P or K has not gone above the N and P or else more males will occur. Obviously this means to avoid overfeeding your plants around this time too.
Never let your medium dry out completely around the 3rd to 4th week of vegetative growth. If you make sure to water occasionally, but not to overwater your plants, you will get those female ratios on the up and up. Overwatering or drying out of the medium will only produce more males. For consistent results in getting more females keeps those mediums moist.
Humidity. Now this is the tricky one. High humidity levels only promote fungi and mold development and lowering humidity levels is the way to cure most of this rot but by keeping those humidity levels up in or around the 70 rH factor will help to produce more females. If you have a low humidity grow room then you should get to hold of a humidifier. Now high humidity levels like 70rH cause the medium to dry out a lot quicker so you got to keep this under control too. Keep those mediums moist and those rH levesl at 70. This will help to improve those female to male ratios. Again, getting them on the up and up.
If you run the 24/0 photoperiod then do not allow those temps to go anywhere above 85 unless you have an equatorial strain. 75 is the best but going a little lower is not a problem for helping those female ratios. If you can get in at around 65 then those females are going to be popping up all over the place. The problem with this is that some growers like to use the 18/6 photoperiod and when the lights are off the temps drop from around 65 to 50 and even less. Try not to be below 55 because this has the adverse effect on the plants producing more males than females. Again between 65 and 75 is where you want to be during the 3rd to 4th week of vegetative growth, the preference being 70.
Invest in a MH Light for vegetative growth. Dump the HPS bulb for flowering later. I have noticed that HPS lighting during vegetative growth simply sends those males to female ratios all over the place. With MH lamps the females are everywhere. Invest in some MH HID lights. It makes all the difference in getting those females to show more often. This is worth repeating! MH Bulbs produce more females under optimal conditions especially if they are present during the 3rd and 4th week of vegetative growth. Surprising enough you can start seedlings under HPS and it will not have an effect on those female ratios. Again the 3rd to 4th week of vegetative growth is what is important here.
No stress during the 3rd to 4th week of vegetative growth. That is all there is to it. If you got your garden growing in optimal conditions without plant stress then the impressive 90% to 95% females start to emerge from standard seed packs. I find that topping is best done at the second to third week of vegetative growth but that this is a little stressful and can lead to those female ratios dropping again. Avoid topping or pruning if you are looking to up the female count.
That is all I have to say for the moment. These little snippets of information in conjunction with what DP uncovered have helped my female ratios considerably. Hopefully you can see the same results too. Have fun getting those environments optimal for females!!!!!!!!