Plant Hardiness Zone(s)
The plant hardiness zones in the state of Iowa range from 4 in the northeast all the way up to 7 in the far southwest. Hemp crops are therefore more suitable to southern Iowa rather than the northern parts.
Iowa falls in the North Temperate Thermal Zone and has cool to mild temperatures. The warmer temperatures in the summer months are more conducive to hemp cultivation, especially in the southern regions where climatic conditions are warmer.
Length of Growing Season
The growing season for hemp should ideally start in late Spring (month of May) once the last frost has thawed and soil conditions are warmer. Planting dates should be set according to soil temperatures rather than a calendar date for optimal germination. Harvesting should take place in late August when the length of the day has shortened to 12 hours. Hemp is a short day plant which means that it will only enter the last phase of maturity once the days have shortened. Harvesting should take place around 8 days after full maturity has been reached.
Average Annual Sunlight
Iowa receives an average of 2,755 hours of sunlight every year and 62.9% of daylight hours are sunny. Hemp requires plenty of sun as the plants are heliotropic and planting in the summer months when the most sunlight is experienced in the state is therefore optimal.
Average Annual Precipitation
Iowa receives an average of 34 inches of rainfall annually with a low of 26 inches in the northeast and up to 38 inches in the southwest. Hemp requires between 10 and 12 inches of precipitation in the summer months for optimal growth. The southern regions of the state are more suitable for hemp cultivation.
The lowest elevation in Iowa is 480 ft above sea level at the Mississippi River with the greatest elevation of 1,670 ft at Hawkeye Point. These elevations are not great enough to have a great impact on hemp cultivation in the state. However, colder conditions at elevation in the northeast can negatively impact a hemp crop.
The soil pH in the state ranges from 4.5 to 8.2. Hemp prefers a pH of between 6 and 7. It is advisable to have soil tested for a specific location within the state to determine the pH and whether it is suitable for hemp cultivation.
There are basically 3 types of soil that occur in Iowa ranging from fine grain to clay. Hemp grows optimally in looser soils which allows the long tap root to reach nutrients located deeper underground. Compact soil like clay is not suitable for hemp and will result in smaller plants that produce less flowering heads.
Crops in Iowa are particularly prone to “green bridge” pests largely affecting early spring vegetation. These pests include slugs, flies, beetles and moths. However, hemp is prone to mites and aphids and controlling these pests is essential before the flowering heads emerge. There is also a potential for mold and fungus growth to affect the heads due to high rainfall and moist conditions in the southwestern regions.
Obtaining A Hemp Grower’s License In Iowa
Under federal law, it is illegal to grow hemp anywhere in the United States without first obtaining a grower’s license from the appropriate regulatory body for the state in which the interested party intends to plant the crop. For information on the legal status of hemp in Iowa, as well as a breakdown of the application process, click here.