by Ed Rosenthal
Regenerated plants tend to have a lot more branching than first-time flowerers, so you should practice branch control (see Pruning). Selective pruning results in fewer flower sites, but the buds on each one grow larger, resulting in more Grade-A flowers.
INDOOR-GREENHOUSE MANIPULATION
Gardeners can use a combination of indoor and greenhouse or outdoor gardening. Plants are started and initially grown indoors to get a head start, then moved outdoors. By starting early with large plants, you can get a jump on the season. This also helps with light deprivation techniques for harvesting more than one crop a year.
Plants grown indoors that are placed outdoors during late spring and during the summer usually need to adjust to the harsh UV rays by keeping them in the shade at first or using an anti-transpirant.
MAXIMIZIING THE INDOOR-GREENHOUSE GARDEN
Some growers can combine indoor gardens and greenhouses. For best results, start plants indoors in late November and let them grow vegetatively for three months until they are fairly large. In February, transfer them to a heated greenhouse. For 8 hours a day during the sunlit period, use supplemental light of 600 watts over every 30-40 sq ft (9-12 m).
This farm in Switzerland produced three crops of small plants over the season. A recently harvested field was just replanted.
Use removable clear polyethylene tunnels to create a greenhouse effect and to conserve the heat at night. Then use black plastic for shading. This farm in Switzerland produced three crops a year using this strategy.
The plants start flowering immediately, because they are receiving more than 12 hours of darkness daily, and ripen by the end of March.
Return the plants to vegetative growth by using the MH light on a timer to break up the dark cycle until they regenerate.
Around May 15th, after growing vegetatively for 6 weeks, force the plants to flower again by covering the greenhouse with blackout material each evening, so they receive only 12 hours of light daily. This results in a harvest around July 15th.
Clear out the old plants and replace them with a new set of plants that have been growing indoors vegetatively for two or three months. They are not as big as the plants moved to the greenhouse in February but have a bit of branching. These plants have to be hardened up to withstand the intense midsummer sun. Use a 30% shade cloth for the first five days, and spray the leaves with an anti-wilt product or anti-transpirant. Grow the plants under natural light for a month, until about August 15th, then force them to flower using a blackout curtain to establish 12 hours of darkness. They are ready for harvest by October 15th.
NUTRIENTS FOR GROWTH
When marijuana is supplied during the vegetative stage with ample amounts of all its requirements, including nutrients, it grows very quickly. If the soil or planting mix cannot meet the plants’ nutrient needs, they require fertilization.
If the plants are suffering from a particular nutrient deficiency, supplying that individual nutrient puts them back on track.
There are many brands of hydroponic and specialized fertilizers available. Most of them have been available for many years and have satisfied customers, otherwise they would go out of business. Try a brand according to the directions provided. If you are satisfied with it, stick with it, if not try another. If friends or garden supply store employees offer you different mixing recommendations or odd combinations of products, test with just one plant first to see if the recommendation is beneficial or perhaps harmful. Generally speaking, use milder not stronger nutrient mixes. Use a conductivity meter to test your water and your nutrient strength. With soluble fertilizers 1,000 ppm or an EC of 2.0 mS is normal strength. If you have hard water, for example 250 ppm, then you should dissolve fertilizer into the water up to 1,000 ppm. Testing pH and adjusting it to between 5.8 and 6.4 is a good idea if you find that your pH is too high or too low.
Plant leaves catch dust. So even if you’re not foliar feeding, it is a good idea to mist the plants every 2-4 weeks with a fine spray, letting the water drip off the leaves. Do this at the beginning of the light cycle, so the leaves are sure to dry completely and the lights are not yet hot. Be careful not to direct the spray near the lights. If the reflector does get sprayed, clean the glass plate so light is not obstructed. Don’t spray when HID lights are on, if there is any chance that the spray will get near the bulbs.
Water quality is important and can cause problems when it is too hard, is contaminated or has strong residual disinfectant like chlorine or chloramine. Collecting rainwater is a good way to obtain soft water.
You may wish to compare two fertilizers and see how their performance in your garden differs. Differences in performance are often due to the quality of water. Fertilizers are a lot like jeans. A brand will fit one person well and the next not so well. Differences in plant response may be caused by the quality of the water. Each fertilizer affects the combination of environmental conditions and plant genetics differently. Some companies offer special fertilizers formulated for hard water.
To improve the flavor of the final product, use unfertilized water for the last seven days. Many of the fan leaves yellow and wither as the remaining nitrogen migrates from old to the new growth. As a result, the buds have less of a green, minty (chlorophyll) taste. They also lose the chemical taste of over-fertilized bud. (For more on nutrients, see Soil)
WATERING AND IRRIGATION
Marijuana is a water-loving plant. It thrives in moist soil and responds to dry conditions first by slowing then halting photosynthesis. As dry conditions continue, the leaves lose turgidity and wilt. Then they dry up. Even a short period without water can result in a dead plant.
Marijuana that has easy access to water can grow to its full potential. This translates to maintaining a moist, but not waterlogged, medium. The reason is that as the planting medium becomes drier, the water bonds more tightly with its molecules. This is expressed as water tension. It costs the plant more energy to tear the water from the medium as water tension increases. When there is a continual water deficit, the plant is not able to get all the water it needs, so all the plant’s processes slow as it adapts to the limiting factor in its environment.
WATER USE ON HOT DAYS
Plant Diameter Square Area Water Requirement
4 feet (1.2 m) 12 sq. ft. (1 m2) 3-3/4 gallons (4 L)
10 feet (3 m) 78 sq. ft. (7 m2) 25 gallons (95 L)
On hot summer days, plants may require as much as a half-inch (1.3 cm) of water.
OUTDOORS
Under natural growing conditions, marijuana planted outdoors uses between 20 and 30 inches (50-75 cm) of water over the season. Most of it is used in June, July, and early August, when the plants are in the vegetative stage and growing rapidly. This is also the period of peak temperature, so the plants use of water increases dramatically because it is used for both photosynthesis and transpiration. Photosynthesis increases in relation to higher light intensity and rising temperature. At its peak, this process uses large amounts of water. Transpiration increases with more light and heat, as it helps cool plants through water evaporation and it draws more water from the roots.
Many factors affect how much water is available to an outdoor garden. In areas where there is regular rainfall or a high water table, plants may need no irrigation. However, areas with a Mediterranean or desert climate, where there is very little rainfall in the summer, cannot support plant growth without irrigation. Water availability also varies by soil type. Clays, mucks, and loams with high content of organic matter hold more water than sandy soil. Water loss to soil evaporation can be eliminated or slowed using mulch, pebbles, or plastic sheeting to protect the soil from the sun, keeping the soil cooler. Container systems that catch and recycle the excess water that would otherwise drain past the roots also conserve water.
Plants growing in soil or soilless mixes should be watered before the medium dries out, but only after the top inch or two (2.5-5 cm) has lost a bit of its moisture. If the soil or mixture drains well, over-watering d
oes not create anaerobic conditions, since the excess water drains. However, soluble nutrients are leached out by over-watering, and unnecessary water use can be costly and environmentally unfriendly.
Plants have problems with some soils not because they are too wet, but because they have too fine a texture and do not hold air between the particles. When roots have no access to oxygenated air, they become stressed and susceptible to attacks by pathogens. (For more on this, see Soil.)
HYDROPONIC WATER USE
Hydroponic gardens typically use one half to two thirds the amount of water that plants grown in the ground require, because almost all the water in a hydroponic system is used directly by the plant.
Gardeners using hydroponic systems just add water to the reservoirs, replenishing water that is either lost to evaporation or used for transpiration, photosynthesis, and general metabolism. Before adding water, check the nutrient levels of the water-nutrient solution remaining in the reservoir. Adjust the nutrients in the water to be added so that when it is combined with what remains in the reservoir, the pH and nutrient levels are within acceptable range.
Growers using active hydroponic systems, such as drip emitters or ebb and flow, should adjust the watering cycle so that the medium never loses its moisture. Each type of medium retains a different volume of water, but media for active systems drain well, so the roots are always in contact with air. The plant’s size and growth stage, as well as the ambient temperature and humidity, all affect the amount of water used, so adjust the recycling schedule accordingly. Cycles might start once every six hours of light during the early stages and increase as the plants grow.
INDOOR WATERING
As with plants growing in the ground outdoors, plants growing in soil or soilless mixes indoors in containers need water once the top layer is no longer moist but before the soil in the root zone dries out. Over-watering is not a problem so long as the soil or planting mix is porous and drains well.
As long as a medium allows both air and water to penetrate, roots remain healthy. If the roots do not have access to air, they grow weak and are prone to attack by bacteria. Planting mixes vary greatly in their water-holding capacity, so the watering regimen must be developed based on the medium and growth stage.
These manual water timers each control one section of a garden. The valve shuts the system off so it can be adjusted easily. Each water meter is turned on manually after the gardener checks the garden and sets the number of minutes for the water to shut off automatically.
The leaky hose lets water drip from its porous sides. The soil was enriched before planting, so the hose carries only water.
With an automated drip you don’t have to physically water the plants in order for them to get adequate water.
When plants are small, they use less water. As they grow, their water needs increase, so the watering schedule should change. In general, plants require more water during vegetative growth than during flowering; however, even during flowering, the plants are most productive when they have easy access to water.
Some growers withhold water for several days before harvesting, but this results in a slightly smaller yield but may result a slight increase of potency. A better practice is to limit fertilizing to improve bud flavor.
FOLIAR FEEDING
Plants can absorb both water and nutrients through their leaves, so the nutrient-water solution supplied to the roots can be misted on the foliage as well. Leaves have stomata that serve the same purpose as pores: They open and close as needed to regulate the absorption of CO2, water, and nutrients. Foliar-fed plants grow faster. It also saves fertilizer compared to soil; about 95% of the fertilizer is absorbed as compared with between 10 and 20% using conventional methods.
Foliar feeding is especially helpful when plants are suffering from a deficiency, because the needed nutrients are delivered directly to the plant parts that need it, the leaves.
You can start foliar feeding as soon as the seeds germinate. Once they have roots, clones also grow faster when they are misted with a water-nutrient solution. Since the ability of young plants to absorb water is limited, a dilute nutrient solution spurs growth. Continue foliar feeding during vegetative growth and early flowering. Stop spraying once the flowers are 3-4 weeks old and are beginning to develop water-trapping crevices. Buds at this stage are susceptible to mold and infections promoted by excess humidity.
PRUNING AND TRAINING
There are probably as many theories about pruning and training and their effect on crop yield as there are cultivators. Pruning and training theories are complicated by the many varieties of marijuana, which have different branching patterns and growing habits. But the intent of pruning and training plants is almost always to increase yield.
Traditionally, gardeners have been more interested in the total yield of their garden space, rather than each plant. Marijuana gardeners have become concerned with the yield per plant primarily because of regulations regarding the number of plants. Medical growers, for instance, may be limited to only a few plants, so each plant is nurtured to produce the highest possible yield. Only when the regulations limit canopy space rather than plant count does it make sense to be concerned about total yield of the space rather than the yield per plant.
Left: The lower portion of the plants was removed to create more air circulation and reduce humidity. The leaves were a net energy drain because they weren’t receiving any light. Right: All the action is in the dense canopy because light can only be used once. Plants were growing in 4" (10 cm) rockwool cubes placed on rockwool slabs. They were fed through drip emitters until they started to drain once every three days.
PRUNING TECHNIQUES
Some pruning techniques increase yield in a given area. In addition pruned plants usually occupy more space than plants left unpruned, so yield per plant may increase substantially with pruning.
Marijuana adjusts well to many kinds of pruning techniques. It can be pruned to become bushy rather than tall, trimmed to only a few branches, cut to fit a space, or stretched out to promote branching. Flowering plants can also be pruned to increase flower production. For more on those techniques, see Flowering.
To make a plant bushy, clip the tip of the growing shoot after the third set of leaves has developed. The branches surrounding the top branch are no longer inhibited from growing and create a rosette of three or four branches. Meanwhile the two top shoots that have been hanging out at the pair of top nodes begin to grow. Other lower branches grow a bit as well. After the plants have grown another three or four sets of leaves, clip the tops again if you would like the plant to grow even bushier. Sometimes the plants are pinched once or twice more during the vegetative stage. Cutting the tips encourages plants to spread out rather than to grow vertically.
The three plants in one container (shown in photo above and on the left in top photo) had the greatest yield. The topped plant, with expanded side branches was the next highest, followed by a single untopped plant.
Indoors, the canopy absorbs virtually all the light, leaving little in the shadows below. For this reason, the understory below the canopy contributes little energy to the plant. Instead, it costs the plant nutrients, increases humidity, and stops air-flow.
Pruning the lower limbs creates more air-flow under the plants and creates cuttings for cloning. It also forces the plant’s growth to the top limbs that get the most light, maximizing yield. These lower leaves and branches should be removed to create an open airspace.
FLAT PLANTS
Selective pruning creates “flat”, two-dimensional plants that can be placed against walls, positioned close to each other, or used in unusual configurations.
Marijuana typically grows leaves on opposite sides of the stem, with each set of leaves perpendicular to the next. Each leaf is attached to the stem at approximately a 90˚ angle, parallel to the ground, positioned to catch light. Opposing branches develop at the nodes between the leaf and stem, so the plant basically has four corners.
These plants were “lollipopped.” The lower branches were removed because they didn’t contribute to yield.
This plant was topped several times and developed into a bush.
These plants have been dwarfed by constant removal of fan leaves. They would have been twice the size if the leaves had remained. If the plants didn’t use the leaves it wouldn’t grow them. Another problem is the black containers baking in the sun absorb the sun’s heat and bake the root ball, damaging the roots. The solution: Paint the containers a light color, wrap them in light colored paper, plastic or fabric, or place them in baskets.
Left to right: Only the tops remain on this plant. Each branch receives its own bamboo stake for support. Use twist ties to bind the stem to the stake. Two months later the four-4 bud trim pays off.
FLORIBUNDING (FIMMING)
Trim the top 80% of the apical growing tip, leaving about 20% intact. The tip develops multiple tops creating a bushy plant laden with heavy branches. Topped branches usually develop two to four new tops for each one cut. Using this technique, a single branch produces six to eight tops.