:smoking: From what breeders and botanists say,
sex is predetermined, but it is labile, meaning it's "set" at the seed stage, but can change under the right conditions, influencing factors,... This is a common thing in nature, even some vertebrates can do this; fish in particular, a few reptiles (including parthenogenesis). In cannabis, if we're talking
strictly about a pre-blooming sex shift, not any form of hermaphrodism, sex reversal, etc., then here's a great article summing it up. Some bits are dated (lighting), but the rest is solid:
As a marijuana grower I always believed that weed seed was genetically predisposed to its sexual orientation as soon as fertilization of the ovule took place in the female. Basically this means that if you take a single female marijuana plant and produced cannabis seeds from her that the ratios are already set in the offspring. If a gender detection test could be established the males could be separated from the females there are then. If this were true then the breeder’s packs of ten seeds per pack could easily turn out to be all males or all females because of this genetic predisposition. However this is not the case!
One of the areas of my interest was in the feminized marijuana seed programs that so successfully charged through-the-roof prices on weed seeds that are reported to grow all females. However, as many marijuana growers like myself have experienced - this is not always the case either!
Feminized cannabis seeds work on the bases that there is a genetic predisposition for the plant to produce females because of special treatment that it gets in the selfing stages of a unique XX female. I won’t go into this in detail here because there is enough information on the process across the entire internet. Anyhow, in an optimal growing environment it is very easy to produce ALL females from these treated female marijuana plants. OPTIMAL is the key word here because in less than optimal marijuana growing conditions strange things start to happen to these feminized weed seeds.
In a single pack of feminized seeds a grower can produce:
Females.
Hermaphrodites.
Males.
Yeah, that’s right. Males! So where are these males coming from and how are they making there way into the feminized cannabis seed process. The answer is a very simple one. Sex is not completely determined in the cannabis plant until a few weeks before flowering. We will talk about this in a moment but now back to the feminized weed seeds.
In optimal cannabis growing conditions feminized marijuana seeds will kick out 100% females. This says a lot for marijuana growing conditions and the actual role they play on cannabis gender development. How many times have cannabis growers seen these effects of multiple genders from Feminized weed seeds? The answer lies clearly in how well they grow.
Weed growers who are growing in non-stressful conditions will never see the male effect from feminized cannabis seeds and so hence it does not exist for them. However over periods time and different weed growing techniques the marijuana grower will eventually see these results when growing in less than optional environments. MALES!
For this reason marijuana growers who choose feminized cannabis seeds should be forewarned to get their growing environments down to a T. If you prevent stress then you prevent males and hermaphrodites appearing in a feminized marijuana seed population. It is as SIMPLY AS THAT.
Now onto the real topic of interest. Boosting those female to male ratios.
As many marijuana growers know cannabis seed banks are not responsible for male to femaleratios. If you get a pack of all males, as many of us have done, then a quick call to your marijuana seed bank can maybe help procure some good substitute freebies with your second order. However some will not go along with this. It depends on your relationship with the marijuana seed bank. Give them a call anyhow, that is my advice, but be discreet and don’t blame the cannabis seed bank or marijuana breeder.
A couple of years ago Dutch Passion released an essay on how to increase mostly females from a pack of weed seeds. This is an excellent piece of work and has helped me to gain more of an interest in this area. In the past few years I have come to develop my own systems to get those ratios on the up and up. Right now I am very happy to report a real increase in my females from standard weed seeds. Sometimes as high as 90% to 95% on a consistent basis. So how is it done?
I prefer standard cannabis seeds for numerous reasons. The first reason being that feminized weed seeds come from hermie plants. Whichever way you look at it, the specially treated plants are hermed and this trait is often expressed in the offspring where conditions are less than optimal. Even with standard weed seeds the hermaphrodite condition is still achievable where stress occurs.
I seem to have noticed that the two most stressful conditions which can cause the hermaphrodite trait occur before marijuana flowering in the vegetative phase of growing is around the 3rd to 4th week of growth before pre-flowering. When the cannabis plant undergoes either heat stress or a problem with the 24/0 or 18/6 photoperiod (whatever vegetative photoperiod choose doesn’t matter, as long as disruptions occur). Even during the initial stages of calyx development males and females are obvious side by side at the node region. This is hermaphroditism due to vegetative growth problems.
In the marijuana flowering period, hermaphrodites generally occur quicker because of an irregular photoperiod than anything else and heat stress certainly helps bananas to pop up in with the marijuana bud. Now, even Sinsemilla cannabis crops will herm towards the end depending on the weed strain. I don’t class this as a typical case of hermaphrodites. It is just something that some weed strains naturally do towards the end of the Sinsemilla procedure.
Anyhow for starters we better reproduce what Dutch Passion have to say about their feminized weed seeds first.
"Feminised Cannabis Seeds"
Courtesy of Dutch Passion
In November 1998 we introduced our "Female Cannabis Seed". We did this after our own experiments showed that from female cannabis 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 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 cannabis seeds as well. Because of the fact that Female marijuana seeds do not grow into female marijuana plants under all circumstances. Thus 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 femalecannabis plant from marijunaa seed, except for the predisposition in the gender chromosomes, also depends on various environmental factors. Not only the origination of entirely male orfemale marijuana plants is partly affected by these environmental factors, the number of maleand female cannabis flowers on a hermaphrodite plant is affected as well.
The environmental factors that influence the sex of the cannabis 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 cannabis 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 marijuana 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 marijuana seedling has three pairs of real leaves (not counting the seed-lobes). This is the moment that male and/or femalepredisposition 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:
- Level of nitrogen and potassium of the seedbed: A heightening of the standard level of nitrogen makes for more female cannabis plants originating from the weed seeds. A lowering of the nitrogen level shows more male cannabis plants. A heightening of the level of potassium tends to show more male marijuana plants, while a lowering of the potassium level shows more female marijuana 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.
- Humidity and moistness of the seedbed: a higher humidity makes for an increase in the number of female cannabis plants from weed seed, a lowering for an increase in male cannabis plants. The same is valid for the moistness of the seedbed.
- Level of temperatures: lower temperatures make for a larger number of female marijuana plants, higher temperatures for more male marijuana plants.
- Colour of light: more blue light makes for female cannabis plants from seed, more red light makes for more male cannabis plants.
- 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 cannabis plants.
Now let me just make a few adjustments here to this. You can do whatever you want to your cannabis 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 cannabis plants hermed because of problems that occurred around this period of the cannabis 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 marijuana plant.
Now I believe that the genders are set in the weed seed however the environment has a massive impact on how this is expressed in the final phenotypic expression of the cannabis plants gender. There are probably many genes that govern this, however lets get into how to up these female ratios.
The Italian Society of Agricultural Genetics agrees the sexual differentiation of cannabis is strongly influenced by environmental factors such as temperature and photoperiod. Anomalies also occur in floral development like the presence of reproductive structures of the opposite sex, or the development of bisexual inflorescences (monoecious phenotype).
At the 3rd to 4th week of vegetative growth make sure that your marijuana 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 weed 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 cannabis plants around this time too.
Never let your medium dry out completely around the 3rd to 4th week of vegetative marijuana growth. If you make sure to water occasionally, but not to overwater your cannabis 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 85F unless you have an equatorial strain. 75F is the best but going a little lower is not a problem for helping those female ratios. If you can get in at around 65F 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 65F to 50F and even less. Try not to be below 55F because this has the adverse effect on the plants producing more males than females. Again between 65F and 75F is where you want to be during the 3rd to 4th week of vegetative growth, the preference being 70F.
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 marijuana plant stress then the impressive 90% to 95% females start to emerge from standard cannabis 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.
