Defoliation (Leaf Removal) During Flowering: A Detailed Guide to Increasing Yields

There are many debates among growers about defoliation, or leaf removal during flowering. Some growers swear by this technique and claim that removing some large leaves increases yields and improves air circulation. Other growers insist that plants perform best without intervention. The truth lies somewhere in between. When carried out correctly, defoliation can increase the amount of active compounds in the flowers in the lower levels and helps prevent mould. Excessive or incorrectly timed leaf removal, on the other hand, can harm plants.

At first glance, it might seem that removing leaves must inevitably harm plants. Leaves are essential for photosynthesis, gas exchange and water evaporation. If you remove too many of them, you slow down the plants’ metabolism and they will grow more slowly. On the other hand, it has been proven that the production of secondary metabolites (terpenes, active compounds, essential oils, flavonoids) is directly influenced by the intensity of the incoming light. It is therefore common for flowers in the lower and shaded parts of plants to be less potent than those at the tops, which are exposed to direct light. According to studies, sensitive defoliation at the beginning of the flowering period can achieve a significant increase in the concentration of secondary metabolites in the lower parts of plants without a drastic reduction in total biomass or a slowdown in growth (1).

Guide to defoliation during flowering

You can use this leaf removal technique for indoor and outdoor growing of photoperiodic and autoflowering plants.

Timing: The best time for targeted leaf removal is when the first buds start to become visible on the plants. In indoor growing, this moment comes approximately two to three weeks after switching to flowering on a 12/12 schedule, or after 3–5 weeks from seed germination in autoflower varieties. Photoperiodic varieties grown outdoors here begin to enter flowering during August.

You may also be interested in: Everything you need to know about switching to flowering

Which leaves to remove: Focus only on the large fan leaves that shade future flowers, and on those hidden in the dense growth in the centre of the plant, where no light reaches them and they prevent free airflow. After the intervention, the plant should be generally more permeable to both light and air. Never remove more than two to three pairs of leaves from one branch at a time (depending on the size of the plant).

Correct technique: Large leaves can usually be torn off easily with a light pull against the direction of growth. Alternatively, you can use sharp garden scissors. If you are removing leaves from several plants at once, remember to disinfect the scissors to prevent the transfer of pathogens.

OUR TIP: In indoor growing, where the light source is stationary, poor light penetration through the canopy tends to be a bigger problem than outdoors, where the Sun illuminates plants from different angles. Some growers deal with this by removing the poorly lit lower branches from plants at the beginning of flowering. Defoliation is only a partial solution, because the lower flowers are far from the grow lights and receive less light energy. Additional LED panels are an excellent solution, as they illuminate the lower part of the canopy. With a relatively small amount of invested energy, unpromising sparse flowers can be turned into hard buds.

Are you looking for more tips and guides for experienced growers and beginners alike? You can find everything about indoor and outdoor growing on the Higarden blog.

Sources: (1) Danziger, N., & Bernstein, N. (2021) DOI:10.3390/plants10091834