Size Matters: The Case For Short Cannabis Plants

As I was learning and teaching myself proper horticultural practices early in my cultivation career, my goal was to grow the largest plants possible, thinking “the larger the plant, the larger the yield.”

This notion is one shared by many first-time growers, especially novice outdoor farmers. Growing 10-foot-tall (or more) trees can without a doubt impress friends and team members.

However, my experience ultimately taught me that the time, resources and energy required to grow and maintain very large plants was not worth it.

The Trouble With Tall Plants

To grow tall cannabis plants, growers must extend the vegetative cycle to grow thicker stalks and more branches. And during longer vegetative cycles, there will inevitably be more resources utilized.

Cannabis remains in its vegetative state when photoperiods exceed 12 hours per day, which means indoor growers must keep lights on for longer periods, increasing production costs. Similarly, greenhouse growers will need to rely more heavily on supplemental lighting during darker winter and spring months to allow the vegetating plants to grow to their colossal size. Outdoor growers might need to start plants earlier in the season in a greenhouse or indoors to get plants large enough before planting them in their fields come spring, thus increasing production costs.

Maintaining taller plants can also be an issue for employees. Defoliating tall plants might require cultivation team members to climb ladders, slowing down the process and increasing the risk of accidents. Because of their increased biomass, large plants require much more support in the form of trellising than medium or small plants, which again can become an arduous task when it needs to be done on a ladder or from a cherry-picker.

When grown outdoors, large plants are also more susceptible to having broken branches—or worse, destroyed main stems—during inclement weather, as the bigger branches weigh down the plant in later growth stages. Similar to trellising, covering large plants during storms can create havoc for cultivation staff. Leaving large plants poorly covered can lead to moisture-related health issues, including bud rot, botrytis and/or powdery mildew.

While growing larger plants in larger containers might save on watering (a larger volume of growing media will generally hold more water, thus reducing watering frequency) there is also a spacing consideration: How much usable biomass are you getting out of your large pot compared to having multiple pots covering the same area that require the same inputs? With most cultivars, three stocky 3- foot plants can yield as much, if not more, usable biomass than a 9-foot plant. Larger plants will have more wasted biomass due to the larger number and size of stems, branches and stalks.

While large plants will typically produce huge buds, it will be difficult to get those to consumers. Huge, beautiful buds will certainly impress even the most novice customer, but they are more difficult to package. Growers are often forced to break down those massive colas to fit into retail packaging, wasting all the time and resources spent growing them.

The Benefits of Smaller Plants

Short and medium plants are easier to defoliate and maintain, as they are closer to regular working height and require less structural support—often, only two or three layers of trellis are required to support the plant and branches—and are more resilient against inclement weather.

Smaller containers are also easier for both employees and machines to work with and move around, helping with facility workflow. And they can be stacked on multi-level racks to maximize the use of available floor space. While a larger plant may yield more than a single small plant, by stacking smaller plants vertically and increasing density, yield per square foot figures can dramatically increase.

From an input perspective, smaller plants will require less supplemental and side lighting (in both greenhouse and indoor environments), as there is not as much foliage through which light needs to navigate. They also will require less frequent and intense defoliating, as even lower and deeper bud structures will receive enough light compared to similarly positioned buds on large plants. Not only will they require less supplemental lighting, short plants also will require less vegetating time, thus saving electricity and other input costs.

Additionally, shorter vegetation cycles will allow greenhouse and indoor growers to get more harvests in their year, and the harvests will be quicker, as there is less unusable biomass to sort through. Ask yourself: are you growing buds? Or stems and stalks? Because, last I checked, the stems and stalks have little-to-no value. I would rather focus on maximizing the productivity and quality of the usable buds rather than growing fibrous material. 

3 Tips to Keep Plants Short

Tip 1: Minimize veg time. To optimize production, ideally plants will grow 24 to 36 inches indoors and 48 to 60 inches outdoors. To keep crops at targeted heights, growers can short-cycle plants, which minimizes cultivation time spent in vegetation. Vegetation should run no more than the length of time it takes for a given cultivar to reach the target size and have strong root development, which some achieve in as little as two to three weeks in tiered indoor grows and up to eight weeks in single level grows.

Beyond adjusting size, short-cycling also reduces the risk of disease or pathogens infecting crops—the quicker the plants are harvested, the less time problems have to manifest. More frequent harvests will also equate to more frequent room decontaminations, again minimizing the risk of critical crop failures or diseases that seep through the entire facility and become systemic. If pathogens do infect a crop, it’s easier to recover from a shorter plant cycle and start anew rather than see six months of vegetation work go up in smoke (and not in a good way).

Indoors growers can more easily dictate the final height of the finished plant by decreasing the amount of light the plant receives earlier in the growth cycle before inducing flowering.

By manipulating the photoperiod and intensity in the vegetation period, growers can ensure that plants are the ideal size by the end of flowering. Often, at the end of the flowering cycle, the plants will be taller than desired and may get too close to light fixtures, which can cause photobleaching or tip burn. Understanding your specific cultivars and their growth patterns is a must, and until cultivar information becomes more widely available, this can only be learned through experience—and trials.

Tip 2: Plant seedlings later in the growing season. Outdoors, the easiest method possible to produce medium-sized plants rather than large ones is to plant seedlings slightly later in the growing season, leaving less vegetative time before the flowering cycle. A shorter vegetative cycle in midsummer can produce very nice medium-sized plants with a stalk infrastructure that only requires two or three levels of trellis for supporting flowering branches, rather than scaffolding-type supports that are sometimes required for supporting very large plants.

(Relatedly, I’ve seen many home growers who want to grow large plants purchase clones from their local dispensary and immediately place them in a media outside, only to have them immediately begin to flower because they are now receiving less light than what is required for vegetative growth. Likewise, the clones’ growth would be stunted because they have been thrust in a cooler environment than they were propagated in.)

The key to short-cycling outdoors is understanding the outdoor environment—more specifically, seasonal temperatures and light levels—so one can predict when it is best to place plants outdoors or germinate seeds to place outdoors to minimize overgrowth.

If temperatures are still low at night, a simple collapsible hoophouse can be placed over young plants outdoors to prevent stunting (no different than what many backyard tomato growers do and have done for decades).

Interestingly, in some latitudes, such as Hawaii, cannabis plants immediately begin to flower when placed outdoors, regardless of what time of year crops are planted. Some home growers choose to vegetate their plants in a greenhouse with supplemental lighting, or do so in an indoor facility, and place the plant outdoors when the plant has reached the target vegetative height. This way, they end up with a plant that is the desired height at the end of the flowering cycle.

Tip 3: Consider autoflowering varieties. Another way to manage plant height is to employ autoflowering plants from seed. Autoflowering plants typically stay very short, between 24 to 36 inches, but it is not unusual for a 48-inch autoflowering plant to appear. The structure of an auto-flowering plant naturally has less lateral side branching and typically yields a large apical or primary bud with short to very short side branches. Autoflowering plants are also conducive to shorter cycles because plants naturally transition to flower 14 to 21 days after germination.

Growing cannabis plants as tall as your living room ceiling might be a fun side project, but, from a commercial perspective, these mammoths present too many challenges to effectively overcome. If growers do want to grow monsters, it’s likely best to do so in the comfort of their own backyards—if nothing else, the shade will be nice.

Kenneth Morrow is an author, consultant and owner of Trichome Technologies. Facebook: TrichomeTechnologies Instagram: Trichome Technologies k.trichometechnologies@gmail.com