Autoflowering cannabis seeds have completely changed the game for growers, with the ability to produce plants that flower by themselves after two to four weeks of growth. Of course, they stand apart from other photoperiod-dependent strains, which rely on a 12-hour dark and light cycle to thrive. Now, new research provides more insight on how transplant timing and container size can impact the growth of autoflowering plants.
Cornell University researchers conducted a study as part of a New York state hemp research program, looking to determine the optimal growth time for a number of autoflower hemp varieties in plugs. The research also examined how transplanting to growing containers or to the field impacts plant growth and yield.
To examine the distinction, researchers planted feminized seeds from a California-based hemp breeding company either directly into three-gallon containers in custom soilless mix with added Mycorrhizea or in plugs. Once the seeds germinated, they were transported into three-gallon pots after eight, 15, 22 and 29 days, and the three autoflower seed varieties (Sunbeam Haze and KG9201 and KG9202) were planted in a field.
Researchers grew plants for 70 days in a controlled environment greenhouse with supplemental LED lighting, maintaining a 82 to 85-degrees F temperature during the day and 73 to 75 degrees F at night. Young plants maintained a humidity as high as 55% to 60%, reducing to 45% as they reached the flowering stage.
Scientists also recorded growth measurements in periodic intervals, including plant height, canopy width and number of branches and buds. Plants were harvested on day 35, to compare vegetative growth, and day 70, and whole plant and bud yield data was also measured.
The results found similar growth for seedlings transplanted from eight- and 15-day-old plugs, compared to those planted directly in a three-gallon container. Transplanting plugs to a container after 22 days also reduced plant height by at least 55% (KG9201, 9202) and by 22% (Sunbeam), compared to direct seeding. Researchers also noted that the total number of branches significantly decreased when transplanting after 22 days, compared to plants from weeds planted directly in a three-gallon container.
The number of buds for Sunbeam Haze was similar for any transplanting method, but researchers observed reduced bud count in both KG9201 and 9202 when plugs were planted at 15 days or more. Bud dry weight reduced significantly in all three strains when transplanted from 15 days or more from plugs.
For Sunbeam specifically, dry weight decreased by 31% and 68% when transplanted from plugs after 22 and 29 days, compared to direct seeding. Dry weight dropped by 22% and 48% for KG9201 and 16% and 31% for KG9202 when transported from plugs after 22 and 29 days, respectively. The results indicate that plant growth saw a reduction of 40% or more when plug seedlings were transplanted after 15 days to three-gallon containers.
Researchers also found that seedlings kept in plug liners for 28 days started flowering after 20 days, as the prolonged stress on the tap root structure induced flowering at the seedling stage.
Direct seeding in the three-gallon containers also produced the maximum number of flower buds with maximum plant height, plant width and the highest number of branches.
Researchers ultimately confirmed that planting the three varieties in three-gallon containers produced the best results, as shown by plant height, width and branch quantity measurements. The results also found that autoflower hemp plants may be sensitive to transplant shock, so growers may consider transplanting seedlings to leather containers earlier in the plant’s life cycle.
The study also found that the best results were observed when plants were transplanted from a liner to the field or large containers within 15 days of seed planting. Ultimately, based on the findings, researchers recommended direct seeding for maximum growth and yield.
