Flowering, Breeding and Propagation

Genetics and Sex in Cannabis

Sex is an inherited trait in Cannabis, and can be explained in much the same terms as human sexuality can. Like a human being, Cannabis is a diploid organism: its chromosomes come in pairs. Chromosomes are microscopic structures within the cells on which the genes are aligned. Cannabis has 10 pairs of chromosomes (n=10), for a total of 20 chromosomes (2m=20).

One pair of chromosomes carries the primary genes that determine sex. These chromosomes are labelled either X or Y. Male plants have an XY pair of sex chromosomes. Females have XX. Each parent contribute one set of 10 chromosomes, which includes one sex chromosome, to the embryo. The sex chromosome carried by the female ovule can only be X. The one carried by pollen of the male plant may be either X or Y. From the pollen, the embryo has a 50/50 chance of receiving an X, likewise for Y; hance, male and female progeny appear in equal numbers (in humans, the sperm carries either an X or a Y chromosome.)

Flowering

Male Plant

Under natural light, males usually start to flower from one to four weeks before the females. Where the photoperiod is artificially controlled, as with electric lights, males respond quickly (in about a week) to a change to short photoperiods and usually show flowers sooner than the females.

Male flowers develop quickly, in about one to two weeks on a vigorous plant, not uniformly. Scattered flowers may open a week or more before and after the general flowering, extending the flowering stage to about four weeks.

The flowering stage continues to demonstrate the male's tall, relatively sparse growth. Most of the flowers develop near the top of the plant, well above the shorter females. The immature flower buds first appear at the tips of the main stem and branches. Then tiny branches sprout from the leaf axils, bearing smaller clusters of flowers. The immature male flowers are closed, usually green, and develop in tight clusters of knob-like buds. The main parts of the male flowers are five petal-like sepals which enclose the sexual organs. As each flower matures, the sepals open in a radiating pattern to reveal five pendulous anthers (stamens).

Inside the ovoid, sac-shaped anthers, pollen grains develop. Initially, pollen sifts through two pores near the top of the anther; then, starting from the pores, longitudinal slits slowly open (zipperlike) over the course of a day, releasing pollen to the wind. Once a flower sheds pollen, it shortly dies and falls from the plant. Normally, male plants begin to die one to two weeks after the bulk of their flowers have shed pollen. Healthy males may continue to flower for several more weeks, but secondary growth seldom has the vigour of initial bloom.

Female Plant

The female plant generally starts to flower later than the male, under either natural light or an artificially controlled photoperiod. Female marijuana plants flower when the average daily photoperiod is less then about 12 to 13 hours. However, some varieties and individuals may flower with a photoperiod of over 14 hours. Some Colombian varieties may not respond until the photoperiod falls below 12 hours for a period of up to three weeks.

The duration of flowering also depends on the particular rhythm of the variety, as well as growing conditions, and whether or not the plant is pollinated. Within these variables, females maintain vigorous growth and continue to rapidly form flowers for a period that ranges from 10 days to about eight weeks.

Females generally do not grow much taller during flowering. Growth emphasises a "filling out," as flower clusters develop from each leaf axil and growing tip. Normally, the flowers arise in pairs, but the pairs form tight cluster of 10 to over 100 individual flowers that are interspersed with small leaves. These clusters are the "buds" of commercial marijuana. Along the top of the main stem and vigorous branches, "buds" may form so thickly that the last foot or more of stem is completely covered. Usually the leaves that accompany the flowers tend toward simpler structure, until each leaf has one to three blades. {Figure 76. Female in full bloom.}

The visible parts of the female flower are two upraised stigmas, one-quarter to one-half inch long, usually white or cream, sometimes tinged with red, that protrude from a tiny, green, pod-shaped structure called the floral bract. This consists of modified leaves (bracts and bracteoles) which envelop the ovule or potential seed. The mature bract is a tiny structure, about 1/8 inch across and 1/4 inch long. When fertilised, a single seed begins to develop within the bract, which then swells until it is split by the mature seed.

Bracts are covered more densely with large resin glands than is any other part of the plant, and are the most potent part of the harvest. Resin glands may also be seen on the small leaves that are interspersed among the flowers.

The differences between male and female Cannabis become more apparent as the plants mature. The same can be said of the differences between varieties. Often, two varieties may appear to be similar, until they actually flowers and fill out to different forms. These appear in many ways: some varieties maintain opposite phyllotaxy with long internodes throughout flowering; bud sizes vary from about one-half inch to about three inches, with a norm of about one to two inches; buds may be tightly arranged along the stem, yielding a "cola" two feet long and four inches thick; and some varieties only form buds along their main stem and branch tips, with a few "buds" forming along the branches.

{Figure 77. Upper left: Buds form thickly into colas along the top of the main stem and branches (full bloom). Upper right: A cola about two feet long. Lower left: A huge leafy cola. Lower right: Long, slim buds form late in the year when light is weak. (these four colas are from Mexican plants.} When a female is well-pollinated, growth slows and the plant's energy goes into forming seeds and thus into the continuation of the species. Some plants (but only the more vigorous ones) will renew flowering even when pollinated. Females that are not well-pollinated continue to form flowers rapidly. This extends the normal flowering period, of 10 days to four weeks, up to eight weeks or more.

Individual flowers are pollinated by individual pollen grains. In a matter of minutes from its landing on a stigma, the pollen grain begins to grow a microscopic tube, which penetrates the stigma and reaches the awaiting ovule wrapped within the bracts. The pollen tube is a passageway for the male's genetic contributions to the formation of the embryo (seed).

The union of the male and female complements of genes completes fertilisation and initiates seed formation. The stigmas, having served their purpose, shrivel and die, turning rust or brown colour. On a vigorous female, the seeds reach maturity in about 10 days. When growing conditions are poor, the seed may take five weeks to ripen to full size and colour. Naturally, all the flowers do not form, nor are they pollinated at the same time - and there will be seeds that reach maturity weeks before others do. Although each flower must be individually fertilised to produce a seed, a single male plant can release many millions of pollen grains. A large female plant can produce over 10,000 seeds.

Sexual Variants in Cannabis

Cannabis has been studied for many years because of its unusual sexuality. Besides the normal dioecious pattern, where each plant bears exclusively male or female flowers, it is not uncommon for some plants to have both male and female flowers. These are called hermaphrodites, or monoecious plants, or intersexes. Hermaphroditic plants form normal flowers of both sexes in a wide variety of arrangements, in both random and uniform distributions.

Natural Hermaphrodites

Some hermaphrodites seem to be genetically determined (protogenous). That is, they naturally form flowers of both sexes given normal growing conditions. Possibly genes carried on the autosomes (the chromosomes other than the sex chromosomes) modify the normal sexual expression. Monoecious varieties have been developed by hemp breeders in order to ensure uniform harvests.

It is also possible that these particular are polyploid, which means they have more than the usual two sets of chromosomes. This kind of hermaphrodite may have XXY (triploid), or XXYY or XXXY (tetraploid) sex chromosomes. However, no naturally occurring polyploids have ever been verified (by observation of the chromosomes) in any population of Cannabis. Polyploids have been induced in Cannabis by using mutagens, such as the alkaloid colchicine.

Whatever then genetic explanation may be, one or more of these natural hermaphrodites may randomly appear in any garden. They are sometimes faster-maturing, have larger leaves, and are larger in overall size than their unisexual siblings. They usually form flowers of both sexes uniformly in time and distribution, and in some unusual patterns. For example, from Mexican seed, we have seen a plant on which separate flowering cluster consisted of both female and male flowers: and upper section of female flowers had upraised stigmas, and a lower section of male flowers dangled beneath the female flowers. In other plants from Mexican seed, the growing tips throughout the plant have female flowers; male flowers sprout from the leaf axils along the main stem and branches. Plants from "Thai" seed sometimes form male and female flowers on separate branches. Branches with female flowers tend to predominate, but branches having mostly male flowers are located throughout the plant.

Abnormal Flowers, Intersexes, Reversals

Gender is set in the new plant at the time of fertilisation by its inheritance of either the X or the Y chromosome from the male (staminate) plant. With germination of the seed, the environment comes into play. Heritage sets the genetic program, but the environment can influence how the program runs. (Sexual expression in Cannabis is delicately balanced between the two.) The photoperiod, for example, controls the plant's sequence of development. Also, the plant's metabolism and life processes are dependent on growing conditions. When the environment does not allow a balance to be maintained, the normal genetic program may not be followed. This is mirrored by abnormal growth or sexual expression.

{Figure 78. Upper left: Abnormal flowers. Lower left: Male flowers on a female plant. Upper right: Sexes on separate branches. Lower right: Male flower in female bud (reversing).}

Abnormal Flowers

Abnormal sexual expression includes a whole range of possibilities. Individual flowers may form abnormally, and may contain varying degrees of both male and female flower parts. For instance, a male flower may bear a stigma; or an anther may protrude from the bracts of a female flower. Abnormally formed flowers are not often seen on healthy plants, although if one looks hard enough, a few may be found in most crops. When many of the flowers are abnormal, an improper photoperiod (coupled with poor health) is the most likely cause. Abnormal flowers sometimes form on marijuana grown out of season, such as with winter or spring crops grown under natural light.

Intersexes and Reversals Much more common than abnormally formed flowers is for the plant's sex to be confused. One may find an isolated male flower or two; or there may be many clusters of male flowers on an otherwise female plant, or vice versa. These plants are called intersexes (also hermaphrodites or monoecious plants). Intersexes due to environment causes differ from natural hermaphrodite in having random distributions and proportions of male and female flowers. In more extreme cases, a plant may completely reverse sex. For example, a female may flowers normally for several weeks, then put forth new, sparse growth, typical of the male, on which male flowers develop. The complete reversal from male flowering to female flowering also happens.

All other things being equal, the potency of intersexes and reversed plants is usually less than that of normal plants. If there are reversals or intersexes, both of the sexes will usually be affected. Female plants that reverse to male flowering show the biggest decline. Not only is the grass less potent, but the amount of marijuana harvested from male flowers is negligible compared to the amount of marijuana that can be harvested from a normal female. Plants that change from male to female flowering usually increase their potency, because of the growth of female flower bracts with their higher concentration of resin. Female flowers on male plants seldom form as thickly or vigorously as on a normal female. Between the loss in potency and the loss in yield because of females changing to males, a crop from such plants is usually inferior, in both yield and potency, to one from normal plants.

Environmental Effects

Many environmental factors can cause intersexes and sexual reversals. These include photoperiod, low light intensity, applications of ultraviolet light, low temperatures, mutilation or severe pruning, nutrient imbalances or deficiencies, senescence (old age), and applications of various chemicals (see bibliography on sex determination).

The photoperiod (or time of planting using natural light) is the most important factor to consider for normal flowering. In 1931, J. Schaffner (105) showed that the percentage of hemp plants that had confused sexual characteristics depended on the time of year they were planted. Normal flowering (less than five percent of the plants are intersexes) occurred when the seeds were sown in May, June, or July, the months when the photoperiod is longest and light intensity is strongest. When planted sooner or later in the year, the percentage of intersexuals increased steadily, until about 90 percent of the plants were intersexual when planted during November or early December.

Marijuana plants need more time to develop than hemp plants at latitudes in the United States. Considering potency, size, and normal flowering, the best time to sow for the summer crop is during the month of April. Farmers in the south could start the plants as late as June and still expect fully developed plants.

If artificial light is used, the length of the photoperiod can influence sexual expression. Normal flowering, with about equal numbers of male and female plants, seems to occur when the photoperiod is from 15 to 17 hours of light for a period of three to five months. The photoperiod is then shortened to 12 hours to induce flowering. With longer photoperiods, from 18 to 24 hours a day, the ratio of males to females changes, depending on whether flowering is induced earlier or later in the plant's life. When the plants are grown with long photoperiods for six months or more, usually there are at least 10 percent more male then female plants. When flowering is induced within three months of age, more females develop. Actually, the "extra" males or females are reversed plants, but the reversals occur before the plants flower in their natural genders.

Some plants will flower normally without a cutting of the photoperiod. But more often, females will not form thick buds unless the light cycle is cut to a period of 12 hours duration. Don't make the light cycle any shorter than 12 hours, unless the females have not shown flowers after three weeks of 12-hour days. Then cut the light cycle to 11 hours. Flowers should appear in about one week.

Anytime the light cycle is cut to less than 11 hours, some intersexes or reversed plant usually develop. This fact leads to a procedure for increasing the numbers of female flowers indoors. The crops can be grown for three months under a long photoperiod (18 or more hours of light). The light cycle is then cut to 10 hours. Although the harvest is young (about five months) there will be many more female flower buds than with normal flowering. More plants will develop female flowers initially, and male plants usually reverse to females after a few weeks of flowering.

Of the other environmental factors that can affect sexual expression in Cannabis, none are as predictable as the photoperiod. Factors such as nutrients or pruning affect the plant's overall health and metabolism, and can be dealt with by two general thoughts. First, good growing conditions lead to healthy plants and normal flowering: female and male plants occur in about equal numbers, with few (if any) intersexes or reversed plants. Poor growing conditions lead to reduced health and vigour, and oftentimes to confused sex in the adult plant. Second, the age of the plants seems to influence reversals. Male plants often show female flowers when the plant is young (vigorous) during flowering. Females seven or more months old (weaker) often develop male flowers after flowering normally for a few weeks.

Anytime the plant's normal growth pattern is disrupted, normal flowering may be affected. For instance, plant propagated from cuttings sometimes reverse sex, as do those grown for more than one season.

Sexing the Plants

The female plant is more desirable than the male for marijuana cultivation. The female flowering clusters (bus) are usually the most potent parts of the harvest. Also, given room to develop, a female generally will yield twice as much marijuana as her male counterpart. More of her weight consists of top-quality buds.

Because the female yields marijuana in greater quantity and sooner you can devote your attention to nurturing the females. Where space is limited, such as in indoor gardens and small outdoor plots most growers prefer to remove the males as soon as possible, and leave all available space for the females. To harvest sinsemilla (seedless female buds), you must remove the male plants before they mature and release pollen.

Differences in the appearance of male and female Cannabis become more apparent toward maturation. During the seedling stage, gender is virtually impossible to distinguish, although in some varieties the male seedling may appear slightly taller and may develop more quickly.

We know of no way to discover gender with any certainty until each plant actually forms either pollen-bearing male flowers or seed-bearing female flowers. However, certain general characteristics may help. Using guidelines like the following, growers who are familiar with a particular variety can often predict gender fairly accurately by the middle stage of the plant's life.

Early Vegetative Growth

After the initial seedling stage, female plants generally develop more complex branching than the male. The male is usually slightly taller and less branched. (Under artificial light, the differences in height and branching are less apparent throughout growth.)

Some plants develop a marked swelling at the nodes, which is more common and pronounced on female plants.

Middle Vegetative Growth

In the second to fourth months of growth, plants commonly form a few isolated flowers long before the actual flowering stage begins. These premature flowers are most often found between the eighth and twelfth nodes on the main stem. Often they appear near each stipule (leaf spur) on several successive nodes, at a distance two to six nodes below the growing tip. These individual flowers may not develop fully and are often hard to distinguish as male or female flowers. The fuzzy white stigmas of the female flower may not appear, and the male flowers seldom opens but remains a tightly closed knob. However, the male flower differs from the female; it is raised on a tiny stalk, and the knob is symmetrical. The female flower appear stalkless and more leaflike.

The presence of premature female flowers does not assure that the plant is a female, but premature male flowers almost always indicate a male plant. Unfortunately, it is much less common for male plants to develop premature male flowers than for female flowers to appear on either plant. For example, in one garden of 25 mixed-variety plants, by age 14 weeks, 15 plants showed well-formed, premature female flowers with raised stigmas. Eight of these plants matured into females and seven became males. Only two plants showed premature male flowers and both of these developed into males. The eight remaining plants did not develop premature flowers or otherwise distinguishable organs until the actual flowering stage at the age of 21 weeks. From these eight, there were four females, three males, and one plant bearing both male and female flowers (hermaphrodite). It does seem, however, that plants bearing well-formed female flowers, on several successive node, usually turn out to be females.

Preflowering

In the week or two prior to flowering and throughout flowering, many common marijuana varieties follow two general growth patterns which depend on gender. With these varieties, you can tell gender by the spacing between the leaves (internodes). For the female, the emphasis is on compact growth. Each new leaf grows closer to the last, until the top of the plant is obscured by tightly knit leaves. The male elongates just prior to showing flowers. New growth is spaced well apart and raises the male to a taller stature. This may by the first time the male shows its classic tall, loosely arranged profile.

{Figure 79. Premature flowers are found on the main stem next to the leaf spurs. Upper left: Early female flower without stigmas. Lower left: Undifferentiated (indistinguishable). Centre: Early male flower. Upper and lower right: Well-formed female flowers on successive nodes usually indicate a female.}

Sinsemilla

Sinsemilla ((The word "sinsemilla" comes from the Spanish, and means "without seeds." It is also spelled "sansimilla.")) is any marijuana consisting of seedless female flower buds. Sinsemilla is not a variety of marijuana; it is the seedless condition that results when the female flowers are not fertilised with pollen.

In the United States, most sinsemilla comes in the form of Thai sticks that are imported from Southeast Asia and Japan. Thai sticks are made up of seedless buds wrapped around a sliver of bamboo or a long wooden matchstick. The buds, which may be on one or more stems, are secured with a hemp fibre wound around the stick. A growing amount of fine sinsemilla now comes from domestic sources, such as Hawaii and California. The grass is usually boxed or bagged with pure buds that are manicured (extraneous leaf removed). Infrequently sinsemilla comes from Mexico and, rarely, from Colombia.

Sinsemilla has a reputation as high-potency marijuana, with a sweet taste and mild smoke. It doesn't have the harsh, gagging qualities of the usual Colombian and Mexican grasses. These qualities, however, have nothing to do with sinsemilla as such. The potency of any grass depends primarily on the variety and development of the plant, and the taste and mildness of the smoke depend on the condition of the plant when harvested and the cure. Heavily seeded grass can be as mild and sweet-smoking as sinsemilla when it is properly handled.

When buying grass, remember that sinsemilla indicates a conscientious effort on the grower's part to bring you the best possible product. Sinsemilla is almost pure smoking material with no wasted weight in seeds. An ounce of sinsemilla has about twice as much smoking material as a typical seeded ounce. Also, any marijuana that is fresh, with intact buds, indicated less deterioration of cannabinoids. {Figure 80. Thai Sticks.}

Sinsemilla is becoming a preferred form of grass with homegrowers, many of whom believe that a seedless female is more potent than a seeded one, reasoning that the plant's energy goes to the production of resin rather than seed. There seem to be no scientific studies on this point. Many experienced growers believe the difference is small, perhaps 10 percent.

From observing the resin glands on the bracts, one sees that they continue to develop in size after pollination. Any difference from the unseeded state is not apparent. Whether pollination does in fact hamper or lessen resin production or potency is questionable. but the effect on the plant as a whole can be dramatic. Usually when the female is well-pollinated, growth noticeably slows, and the plant enters the last phase of life, which is seed set. Seed set is a period of incubation, in which the seeds grow and reach their mature state. New growth forms more slowly and lack the vitality of the bloom before pollination. The plant's reaction to pollination is relative. The more thoroughly pollinated the female is, the more pronounced the change in rhythm from vigorous to incubation. A plant on which only a few flowers have been fertilised continues to actively form flowers as sinsemilla.

Not all plants react alike to pollination. When the weather is good and the plant vigorous, even a well-seeded plant may bloom a second or third time before the rate of growth starts a final decline.

To put this in perspective, the main advantage to growing sinsemilla is that the plant remains in a flowering state for a longer period of time. Flowers may rapidly form for four to ten weeks. The flower buds develop larger and more thickly along the stems, yielding more top-quality grass (more buds) than in the seeded condition.

Anyone can grow sinsemilla. Simply remove the male plants before they release pollen. Given a normal spring planting, males usually flowers in August and September, but may being to flower as early as mid-July. Under artificial lights, males sometimes flower after only three months, and before the grower has shortened the photoperiod. Even though the females are not flowering, remove the males from the room before any flowers open. Indoor, the pollen will collect as dust and can fertilise the females weeks later.

Male flowers mature quickly, in about one to two weeks after the immature buds are first visible. Check each plant about twice a week to make sure you harvest all the males before any shed pollen. If you can't visit your garden consistently, then thin the garden, using the preceding section on "Sexing" as a guide. Even though you may not get all the males, the females will be more lightly seeded. Actually, even in carefully watched gardens, the females may have a few seeds. Pollination may come from on occasional male flower on a basically female plant, or a female may reverse and form male flowers. And pollen may come from a neighbour's garden, a problem that is becoming more common. But in practical terms, an occasional seed makes no difference. The female can form thousands of flowers, and when only a few are pollinated, there is little impact on the plant's growth.