by Robert Connell Clarke
Latitude and Photoperiod
Change in photoperiod is the factor that usually triggers the developmental stages of Cannabis. Photoperiod and seasonal cycles are determined by latitude. The most even photoperiods and mildest seasonal variations are found near the equator, and the most widely fluctuating photoperiods and most radical seasonal variations are found in polar and high altitude locations. Areas in intermediate latitudes show more pronounced seasonal variation depending on their distance from the equator or height in altitude. A graph of light cycles based on latitude is helpful in exploring the maturation and cycles of Cannabis from various latitudes and the genetic adaptations of strains to their native environments.
The wavy lines follow the changes in photoperiod (daylength) for two years at various latitudes. Follow, for example, the photoperiod for 400 north latitude (Northern California) which begins along the left-hand margin with a 15-hour photoperiod on June 21 (summer solstice). As the months progress to the right, the days get shorter and the line representing photoperiod slopes downward. During July the daylength decreases to 14 hours and Cannabis plants begin to flower and produce THC. (Increased THC production is represented by an increase in the size of the dots along the line of photoperiod.) As the days get shorter the plants flower more profusely and produce more THC until a peak period is reached during October and November. After this time the photoperiod drops below 10 hours and THC production slows. High-THC plants may continue to develop until the winter solstice (shortest day of the year, around December 21) if they are protected from frost. At this point a new vegetative light cycle starts and THC production ceases. New seedlings are planted when the days begin to get long (12-14 hours) and warm from March to May. Farther north at 600 latitude the day length changes more radically and the growing season is shorter. These conditions do not favor THC production.
Light cycles and seasons vary as one approaches the equator. Near 200 north latitude (Hawaii, India, and Thailand where most of the finest Cannabis originates), the photoperiod never varies out of the range critical for THC production, between 10 and 14 hours. The light cycle at 200 north latitude starts at the summer solstice when the photoperiod is just a little over 13 hours. This means that a long season exists that starts earlier and finishes later than at higher latitudes. However, because the photoperiod is never too long to induce flowering, Cannabis may also be grown in a short season from December through March or April (90 to 120 days). Strains from these latitudes are often not as responsive to photoperiod change, and flowering seems strongly age-determined as well as light determined. Most strains of Cannabis will begin to flower when they are 60 days old if photoperiod does not exceed 13 hours. At 200 latitude, the photoperiod never exceeds 14 hours, and easily induced strains may begin flowering at nearly any time during the year.
Equatorial areas gain and lose daylength twice duringthe year as the sun passes north and south of the equator, resulting in two identical photoperiodic seasons. Rainfall snd altitude determine the growing season of each area, but at some locations along the equator it is possible to grow two crops of fully mature Cannabis in one year. By locating a particular latitude on the chart, and noting local dates for the last and first frosts and wet and dry seasons, the effective growing season may be determined. If an area has too short an effective growing season for Cannabis, a greenhouse or other shelter from cold, rainy conditions is used. The timing of planting and length of the growing season in these marginal conditions can also be determined from this chart.
For instance, assume a researcher wishes to grow a crop of Cannabis near Durban, South Africa, at 300 south latitude. Consulting the graph of maturation cycles will reveal that a long-photoperiod season, adequate for the maturation of Cannabis, exists from October through June. Local weather conditions indicate that average temperature ranges from 60~ to 80~ F. and annual precipitation from 30 to 50 inches. Early storms from the east in June could damage plants and some sort of storm protection might be necessary. Any estimates made from this chart are generally accurate for photoperiod; however, local weather conditions are always taken into account. Combination and simplification of the earth’s climatic bands where Cannabis is grown yields an equatorial zone, north and south subtropical zones, north and south temperate zones, arctic and Antarctic zones. A discussion of the maturation cycle for Cannabis in each zone follows.
Equatorial Zone – (15 south latitude to 15 north latitude)
At the equator the sun is high in the sky all year long. The sun is directly overhead twice a year at the equinoxes, March 22 and September 22, as it passes to the north and then the south. The days get shortest twice a year on each equinox. As a result, the equatorial zone has two times during the year when floral induction can take place and two distinct seasons, These seasons may overlap but they are usually five to six months long and unless the weather forbids, the fields may be used twice a year. Colombia, southern India, Thailand, and Malawi all lie on the fringes of the equatorial zone between 10 and 15 latitude. It is interesting to note that few if any areas of commercial Cannabis cultivation, other than Colombia, lie within the heart of the equatorial zone. This could be because most areas along the equator or very near to it are extremely humid at lower altitudes, so it may be impossible to find a dry enough place to grow one crop of Cannabis, much less two. Wild Cannabis occurs in many equatorial areas but it is of relatively low quality for fiber or bud production. Under cultivation, however, equatorial Cannabis has great potential for bud production.
Northern and Southern Subtropical Zones – (15 to 30 north and south latitudes)
The northern subtropical zone is one of the largest Cannabis producing areas in the world, while the southern subtropical zone has little Cannabis. These areas usually have a long season from February-March through October-December in the northern hemisphere and from September-October through March-June in the southern hemisphere. A short season may also exist from December or January through March or April in the northern hemisphere, spanning from 90 to 120 days. In Hawaii, Cannabis cultivators sometimes make use of a third short season from June through September or September through December, but these short seasons actually break up the long subtropical season during which some of the world’s most potent Cannabis is grown. Southeast Asia, Hawaii, Mexico, Jamaica, Pakistan, Nepal, and India are all major Cannabis producing areas located in the northern subtropical zone.
North and South Temperate Zones – (30 to 60 north and south latitudes)
The temperate zones have one medium to long season stretching from March-May through September-December in the northern hemisphere and from September-November through March-June in the southern hemisphere. Central China, Korea, Japan, United States, southern Europe, Morocco, Turkey, Lebanon, Iran, Afghanistan, Pakistan, India, and Kashmir are all in the north temperate zone. Many of these nations are producers of large amounts of fiber as well as Cannabis. The south temperate zone includes only the southern portions of Australia, South America, and Africa. Some Cannabis grows in all three of these areas, but none of them are well known for the cultivation of Cannabis.
Arctic and Antarctic Zones – (60 to 70 north and south latitudes)
The arctic and antarctic zones are characterized by a short, harsh growing season that is not favorable for the growth of Cannabis, The arctic season begins during the very long days of June or July, as soon as the ground thaws, and continues until the first freezes of September or October. The photoperiod is very long when the seedlings appear, but the days rapidly get shorter and by September the plants begin to flower. Plants often get quite large in these areas, but they do not get a long enough season to mature completely and the cultivation of Cannabis is not practical without a greenhouse. Parts of Russia, Alaska, Canada, and northern Europe are within the arctic zone and only small stands of escaped fiber and Cannabis grow naturally. Cultivated bud strains are grown in Alaska, Canada, and northern Europe in limited quantities but little is grown on a commercial scale. Rapidly maturing, acclimatized hybrid strains from temperate North America are probably the best suited for growth in this area. Fiber strains also grow well in some arctic areas. Breeding programs with Russian Cannabis ruderalis could yield very short season bud strains.
It becomes readily apparent that most of the Cannabis occurs in the northern subtropical and northern temperate zones of the world. It is striking that there are many unutilized areas suitable for the cultivation of Cannabis the world over. It is also readily apparent that the equatorial zone and subtropical zones have the advantage of an extra full or partial season for the cultivation of Cannabis.
Strains that have become adapted to their native latitude will tend to flower and mature under domestic cultivation in much the same pattern as they would in their native conditions. For example, in northern temperate areas, strains from Mexico (subtropical zone) will usually completely mature by the end of October while strains from Colombia (equatorial zone) will usually not mature until December. By understanding this, strains may be selected from latitudes similar to the area to be cultivated so that the chances of growing Cannabis to maturity are maximized. The short season of Hawaii, Mexico, and other subtropical areas constitutes a separate set of environmental factors (distinct from the long season) that influence genotype and favor selection of a separate short season strain. The maturation characteristics can vary greatly between these two strains because of the length of the season and differences in response to photoperiod. For that reason, it is usually necessary to determine if Hawaii and California strains have been bred specifically for either the short or long season, or if they are used indiscriminately for both seasons. Sometimes the only information available is what season the ~1 seed plant was grown. It may not be practical to grow a long-season strain from Hawaii in a temperate growing area, but a short season strain might do very well.