Chapter 20

Figure 30 is a hypothetical plot of the increase in potency of a male plant and a female during the course of their growth. (Potency is measured by the percentage by weight of THC in a dried sample of the uppermost leaves or growing shoots until flowers appear.) It shoes that generally potency increases as the plant develops. Cues such as phyllotaxy changes and rate of growth are helpful indicator to changes in development and the chronological age of the plant has little significance.

The development of the cannabinoids, resin glands, and, in practical terms, the potency in the living plant is not clearly understood. We believe that,, for the most part, potency does not increase steadily throughout the entire plant. Rather, each plant part reaches a point of maximum potency as it individually develops. A leaf that is formed when the plant is four weeks old does not increase in potency during the rest of the season. To say that potency is increasing means that the leaves that are now forming are more potent than those previously formed.

We also believe that cannabinoid formation is very fast as each plant part forms. Once matured (for example, when a leaf is fully expanded), cannabinoids are decomposing. This is one reason why the potency can decrease as well as increase during growth, especially late in the season, after the flowers have formed. The practical aspects of these points are detailed in the following sections.

Harvesting During Growth: Leaves and Growing Shoots


We have emphasised that you should harvest grass during the course of the season. One reason is to assure yourself a return for your efforts. It is a sad commentary on our times that the greatest danger in growing marijuana outdoors is that the plants may be ripped off. On a more positive note, vegetative shoots and leaves can be surprisingly potent and should be sampled.

The potency of each new set of leaves is higher than the last pair until a plateau is reached, usually during the middle of vegetative growth. Thereafter potency of new leaves stays about the same as in those preceding. Often there is a noticeable decline in potency just prior to flowering. Leaves that form during flowering are usually more potent than those formed during the vegetative plateau. Leaves that form after the bloom are less potent.

Of course, not all varieties or individual plants will follow this rhythm. Faster-developing plants may reach the plateau sooner, and slower plants later. Potency of plants that have a longer life cycle may stay at the vegetative plateau for several months. Some plants do not seem to experience any drop in potency before flowering. Potency of these plants continues to increase gradually after the initial quick increase during early vegetative growth.

Whenever you harvest green leaves during growth, you should always take the uppermost leaves, since these are the most potent. Also, the smaller leaves that form on the branches are more potent than the large leaves on the main stem. These large stem leaves (fan, shade, or sun leaves) are often the first leaves that growers pick. But these are the least potent of all leaves, and the may not get you high at all. As long as these leaves are healthy and green, let them stay on the plant for the plant's growth. Many growers simply use these leaves for mulch or compost as they die.

Don't think that you should harvest each leaf as soon as it appears; this procedure would seriously affect normal growth and result in a small harvest of buds. The potency of individual leaves does not increase during the course of the season, but the decrease in potency is not great. Some of the loss in potency may even be made up for by the loss in tissue weight that a leaf experiences as it dies. Many growers prefer to harvest leaves during growth only after they lose colour, preferring the taste of the smoke to that of green leaves.

Leaves should always be harvested if they die; with indoor gardens, remove any leaves that show signs of insects or other pests.

Do keep yourself supplied with grass (that is the reason you are growing the plant); just don't overdo it. The main harvest is made up of buds, and you want a large, healthy plant that can support vigorous flowering. The larger and healthier a plant is, the more leaf you can harvest without seriously affecting the plant.

Growing Shoots

You may prefer not to clip the growing shoot of the main stem. This forms the largest and most potent cola by harvest time. Plants grown close together usually are not clipped, so that the plants may grow as tall as possible. Where there is much space between plants, the main shoot is clipped to encourage the plant to develop its branches, which fill the available space.

The potency of growing shoots follows the rhythm described for new leaves. However, growing shoots can be the most potent parts of the harvest when picked at the right time. Shoots sometimes reach a very high peak of potency during the middle of vegetative growth. Outdoor gardens should be samples from mid-June through July, since this is the period in which shoots usually reach their peak.

Potency also fluctuates according to local weather conditions. Try to harvest after a period of clear, sunny weather. Potency may declining for several days after a period of cloudy weather or heavy rainfall. After a heavy rain, harvest the shoots a week or two later, since the shoots often peak in potency during a burst of fast growth.

Growing shoots can be harvested from each plant at least twice during growth. The first clipping may not give you much worthwhile grass, but it is done when the plants are young (roughly six weeks old) to force the plant to develop several growing shoots which are harvest about six to eight weeks later. The main shoot is clipped, leaving about four or five nodes below the cut. Two shoots should start to grow from each node, the strongest at the top of the plant and the weakest at the bottom. (This difference is more pronounced under artificial light, since the light is strongest on the top of the plants.) Each plant should produce at least six strong growing shoots after this first clipping. The yield from growing shoots can be considerable (especially during the summer marijuana drought) and will probably keep you supplied until the main harvest.

A third harvest of shoot can be made later if the plants have a long growing season or are indoors. You don't want to clip shoots from the plants just prior to or during flowering, since doing so cuts down on the harvest of buds. Each plant should have at least twelve growing shoots after being clipped twice previously. You might harvest only a few shoots from each plant if the time for flowering is near.

Male Plants

Male plants usually do not have the dramatic increase in potency during flowering that the females do. Male flowers take about two weeks to mature, from the time they are first visible as tiny knob-like buds. New flowers continue to appear for several weeks.

When male flowers open and are about to release pollen, they reach their maximum potency. Since all flowers do not mature at the same time, for maximum potency the plants should be harvested after the first few flowers have opened.

Male flowers actually make up little of the total weight of the harvest, and few new leaves form once flowering begins. There is no significant loss in either potency or yield if the male is harvested before its flowers open. Once male flowers appear, there is little change in their potency. Also, once the flowers do open and release pollen, they shortly fall from the plant and are lost to the harvest.

Males should therefore be harvested before any flowers open unless you want the females to produce seeds. In a small garden, male flower clusters can be individually harvested as they mature. Most growers treat male flowers more as a novelty. Potency of male flowers is quite variable, and seldom are they as good as the female flowers. To remove male plants, cut them near the base of the stem. Don't rip them up by the roots if they are near females that will be left to grow.

Male plants normally begin to lose their vigour after the initial bloom. When the weather is mild, or the plants are indoors, they can be encouraged to bloom a second and sometimes a third time before they finally die.

Harvesting Female Buds

The decision of when to harvest females can be simplified by understanding that you want to pick the buds after they have developed fully, but before degradation processes begin to lower potency. There are two criteria you can use to tell when the plants have reached full bloom. The first is recognising the rhythm, with which the plants are blooming. A second is the condition of the flowers as judged by the health of the stigmas and the colour of the resin.


Since sinsemilla flowers are not pollinated, the flowering period may last for many weeks. The most common rhythm for sinsemilla is that plants go through a stage of rapid bud formation, and the plants do indeed bloom. This bloom often lasts four to five weeks. The bloom ends when the rate at which new flowers form noticeably declines. At his time you should be able to sense that the bloom is completed. Buds are at their peak potency about one week after flower formation slows. This is the time to harvest. True, the plant may continue to grow slowly, but the main harvest is ready and should be taken.

With sinsemilla, some marijuana varieties have an extended bloom that may last more than two months. With this rhythm, the rate at which the buds form is drawn out, and progresses at a slower but steadier pace. The point at which the bloom is essentially over may not be as obvious as in the first case. Here, use the condition of the buds to make your decision. Stigmas wither first at the base of the buds (older flowers). Those stigmas at the top of the buds (younger) will still be white and healthy, although their tips are often brown. Harvest the plants when about half the stigmas in the buds have withered. The coating of resin glands should still be clear or white, with only a few golden or browned gland heads.

A third type of flowering rhythm is sometimes seen on plants from Thai seed. Flower buds bloom and ripen at different times. These plants also have an extended flowering stage that can last for over two months. You may choose to harvest individual buds, colas, or branches as they ripen.


If your primary interest is seeds, the plant should be harvested after the seeds have developed their mature colour. Mature seeds can be seen splitting their sheaths or bracts. When enough seeds have ripened, the plants should be harvested. If the plants are left in the ground and die, many of the seeds will fall from the plant.

For most growers, potency will be of primary interest, seeds only a secondary. With seeded marijuana, flowering is initially rapid until the plant is well-pollinated. If pollination occurs early in flowering, the plants often bloom for another week or two. Generally, you want the plants to flower for at least four weeks before picking, and usually longer, about six to seven weeks.

With seeded marijuana, the bloom is of shorter duration than with sinsemilla. Once growth slows, wait another two to three weeks before harvesting. All the seeds may not be matured, particularly at the top of the bud. But potency of the buds should be about maximum at this time.


Because of such variables as variety and growing conditions, there can be so much variation in the ripening process that no one criterion for judging when maximum potency is reached will be reliable for all cases.

Warm, sunny weather encourages rapid flowering and a long period of receptivity by the stigmas. Cool, rainy weather can wither the stigmas and dampen the vigour of the bloom.

If brief frost or long, cool rain has withered the stigmas, use the plants' growth as a guideline, because ultimately this is the most important criterion. You want the buds to reach a mature size, and to ripen for about another week. You do not want the buds to be left on the plant longer than necessary.

Ideally, harvesting should follow a period of warm, sunny weather. In northern and mountainous parts of the country, many tropical varieties will note flower until late in the season, when the weather has cooled and night-time frosts are threatening. Most mature plant can withstand mild frosts and continue to grow well if daytime temperatures are mild. In this case, let the plants mature, since formation of the buds is more important than the weather in determining potency. Watch the plants carefully, and harvest when the buds reach mature size. Marijuana killed by frost may smoke harshly, but potency does not seem affected. Well-formed buds should be picked if heavy rains are expected. Cannabinoids are not water-soluble, but gland heads will be washed away.

Barring a catastrophe, such as a long frost, death to Cannabis is usually not sudden. The plants will continue to grow, and may infact rejuvenate the next year if the stalks are left in the ground. But after the main bloom, the growth that follows is usually much less vigorous and sometimes forms abnormally. Leaves at this time are simplified, and have one blade. Later leaves are smaller, and tend to have entire margins (no serrations). Sometimes they are twisted or misshaped, as are the flowers that form along with them. This slow growth that follows the initial bloom will contribute little to the weight of the harvest. Additionally, this post-bloom growth is much less potent than the original bloom. Resin glands on these plant parts are feeble and poorly developed. When this abnormal growth forms, the time for harvesting is past. {See Figure 83.}

When a plant seems to persist in growing, and you are not sure bloom is past, the best procedure to follow is to try for a double harvest.

Double Harvests

Most marijuana plants take at least five months to reach maturity. Once the plant has reached maturity, it is forming its most potent marijuana, and should not be cut down completely. You can often induce the females to flower a second (and sometimes a third) time, especially if the plants are indoors or if the weather is expected to stay mild for several more weeks.

To encourage a second bloom, first take the bulk of the harvest: all but the smallest buds, and most of the leaf. Some green leaves should be left on the plant to maintain the plant's growth. After harvesting, give the plants a thorough watering, and water with a soluble, complete fertiliser that provides a good supply of both N and P. This will encourage new growth and continued flowering.

Indoors, the best procedure is to treat the plants like a hedge. Cut all the plants back to equal heights, about two to three feet tall. Remove most of the grass, but again leave a few green leaves on the plant. Don't remove lower branches even if they are leafless, since these will sprout again. Lower the light system to the tops of the plants, and maintain the daily cycle at about 12 hours. The second crop of buds will be ready for harvest in four to eight weeks. With this system, the plants appear like dense hedges of buds. If the second crop of buds forms quickly, you should try for a third crop. Continue to fertilise the plants regularly, and watch for signs of magnesium deficiencies, which often show up when the plants have been growing for an extended time.

Double and triple harvests are one of the benefits of indoor growing. Although plants are relatively small indoors, the original harvest of buds can be triples in the next four months.

Potency and Decomposition

We have said that when buds are picked too late, the potency may decline because of decomposition of the cannabinoids, especially THC.

In section 21, Tables 26-29 give measured rates of decomposition of the major cannabinoids due to exposure to light and air. Light rapidly decomposes THC into unknown products (possibly polymers (122,164)). Light also converts CBD to CBS and CBC to CBL. Air (oxygen) slowly converts THC to the less active CBN. Conversion to CBN is hastened by higher temperatures.

Degradative processes do not occur as quickly in the living plant as when the cannabinoids are purified or in solution, as is shown by the data in Tables 27-30 in section 21 {Tables on disk only}. Resin glands seem to function well in storing the cannabinoids in dried plant material. However, the rates of decomposition in Tables 27 and 28 are for samples exposed to north light and a maximum of 80F temperatures. Temperature would be higher, and light stronger, under full sunlight.

Studies with fresh plant material usually show negligible CBN content in fresh marijuana from immature plants. When mature buds are tested, their CBN content is generally equal to at least five percent of their THC content. When growing temperatures are higher, such as in the tropics, CBN content can account for more than 20 percent of the original THC. Even if we assume a low figure, such as five percent conversion of THC to CBN, there is actually a much greater decline in THC content because of the simultaneous degradation of THC by light.

When the slow rate at which THC oxidises to CBN is considered, five percent decomposition in a period of less than two months represents considerable exposure of the THC to air, and most of this exposure occurs in the last critical weeks when the resin glands begin to degenerate. Plates 8 and 11-13 show the condition of the resin glands on several different kinds of marijuana.

Stalked glands that cover the female flower bracts sometimes rupture or secrete cannabinoids through pores in the glands head. Secretion is not a continuous flow, but more of an emptying of the glands' contents. At this time, gland heads may dehisce. Also, because of their abundance and raised positions, resin glands on the female bracts are exposed to strong sunlight and possible physical damage. These conditions may explain the significant decline in potency of buds that are overripe.

Leaves are also affected by decomposition of the cannabinoids, but not as quickly or seriously as the buds, probably because the resin glands on the leaves are most numerous on the undersurface, where they are somewhat protected from light. These glands rarely rupture or secrete cannabinoids. Often they are intact, clear, and apparently unchanged for many weeks on the living plant.

As the plates show, one can, with the naked eye, see the glands change colour, from colourless or white to golden, and then to reddish or brown. THC is colourless. If the colour changes of the resin do indicate decomposition of THC, then decomposition in the stalked glands that cover the buds can be considerable.

We have smoked buds that seemed to lose about half their potency when left on the plant for an addition three weeks. Colour changes are after the fact. If many of the glands are beginning to brown, the grass should be harvested.

Timing the Harvest

Many growers will disagree with us on when the best time is to harvest the buds (female plants). When the plants are left in the ground, and are alive but past the main bloom, the resinous qualities of the plant may become more apparent. The bracts and tiny leaves may swell in size, and the leaves feel thicker. The coating of resin glands will change colour. Leaves often yellow and fall form the plant. Much of the green colour in the flowering buds may also be lost. Harvests of these buds more closely resembles commercial Colombian grass than typical homegrown. The resin content of the dried buds may be higher, and the grass will smoke more harshly than if the buds were younger when picked. You may prefer these qualities in your grass, and some growers insist this grass is stonier. We feel that the grass will give you the highest high when it is picked as described previously. Smoking is a personal experience, and you should try different approaches and come to your own conclusions.

The first time you grow marijuana is largely a learning experience. Most growers can't wait to start their second crop, because they are certain that they'll improve on both the quantity and the quality of their crop, and this is usually true. The wise grower will not put all his proverbial eggs in one basket. It is a good idea to monitor potency by taking samples every few days when harvest time is drawing near, just as such monitoring is for deciding when to harvest growing shoots during vegetative growth.

In any garden, some of the plants will mature sooner than others. Use the plant(s) that is earliest to mature to decide at what point in its development the plant reaches maximum potency. This finding then serves as a guide for harvesting the rest of the plants.

Try to use buds from approximately the same position on the plant each time you sample. Take only enough to make a joint or two. The more you standardise your testing (and this includes your smoking evaluation), the more accurate your results may be.

Final Harvesting

The time of harvest is a time of joy. It is also a time for caution. Unless the safety of your garden is assured, you will want to harvest quickly, quietly and as efficiently as possible. Ideally, each plant is harvested as it matures, but some of you will have to harvest all at once.

It is best to take cardboard boxes or large, sturdy bags to carry the harvest. You want to harvest the plants with as little crushing or damage to the flowers as possible.

Bring a strong knife, heavy shears, or clippers for cutting the stalks. The quickest way to harvest is to cut each plant at its base. Once the plants are on the ground, cut the stalks into manageable lengths for boxing or bagging. Separate large branches as needed for packing.

The bagged or boxed material should be moved to the curing or drying area as soon as possible. If you let the plants sit in the trunk of a car or in plastic bags, they will start to ferment and small in less than a day.