Monoecious & Dioecious Varieties: What It Means for Hemp Growers

A plant variety can be female, male, or hermaphroditic. The way we classify a plant’s sexual characteristics is by labeling them as either monoecious or dioecious. 

Historically, industrial hemp varieties have been dioecious, plants that have distinct male and female plants. In a temperate climate with 12 to 14 hours of daily sunlight, the ratio of male to female plants in a dioecious population will be equal. However, a dioecious variety of male-to-females ratios can change dramatically under stress from nutrient excess or deficiency, extreme temperatures, and radical light cycle change.

Using selective plant breeding, monoecious industrial hemp varieties have become more prevalent. Monoecious varieties exhibit both male and female reproductive organs on the same individual plant. Without plant breeding, intervention, and maintenance, hemp varieties would revert to their natural dioecious state. 

Plant breeders, primarily in Europe, have selected for monoecious hemp varieties because they produce higher yields of grain and hurd or shive per acre compared to dioecious varieties. Monoecious hemp varieties are optimal for growers looking to take a whole-plant approach, growing a single hemp crop for multiple purposes, including fiber, grain, and oil extraction. 

Generally, monoecious hemp varieties have undergone 8 to 10 generations of intensive selective breeding in order to achieve genetic stability, ideal traits, and standard performance variables. Monoecious plant varieties produce a range of ratios of male and female sexual reproductive organs expressed on a single plant. 

Male reproductive organs are found at the bottom of a seed-producing branch, while female reproductive anatomy is above the male parts. Prior to flowering, a plant’s sex is largely indistinguishable. After flowering, male flowers die soon pollen is shed, while female plants live and develop seeds.

It’s important to realize that a monoecious hemp variety does not ensure that 100% of plants will be monoecious. A 100% monoecious hemp variety will produce a crop with a range of plant types - less than 5% males, less than 5% females. Factors like soil type, climate, precipitation, geography, and the environment will have an effect on an individual plant’s percentage of female to male flower ratio.

Hemp breeders rely on the Sengbusch Classification System, a guide that defines the five degrees of monoecious characteristics. The scale can be found here.

All mostly male plants with any female flowers are genetically XX females and allowable under AOSCA and the OECD Seed Scheme roguing requirements for variety purity.

International Hemp has the exclusive license to two monoecious varieties, Henola and Bialosbrezskie bred by the Institute of Natural Fibers and Medicinal Plants in Poznan, Poland. For more information about monoecious hemp varieties or International Hemp’s available industrial hemp seed, contact us at info@international-hemp.com.