Time of harvest of hemp as a fibre crop will depend on specifications provided by fibre contractors.
As a rule of thumb, textile application crops need to be cut when the male plants (or flowers in monoecious varieties) are shedding pollen, prior to seed setting on female plants (flowers). At this developmental stage, bast fibre is not heavily lignified, which allows for obtaining smooth, high quality fabrics. Delayed harvesting should be avoided as it results in developing coarser fibres, not suitable for certain textile applications. After harvest for textile applications, hemp stalks have to be retted. Note that under this management scenario a grower will not get income from hemp grain, but fair price should be negotiated with the buyer for high quality fibre.
Some hurd buyers prefer white fibre for their applications that can be derived from unretted (or only slightly retted) stalks; therefore, the stalks should be baled shortly after harvest, as soon as the stems are sufficiently dry (12-16%). Baling stems too wet may result in continuation of the retting process in the bale, or even worse, may cause rotting and hence severe loss of fibre quality/yield. Hurd buyers demand weed-free bales as volunteer cereals, wild oats, Canada Thistle, etc. contaminate hurd fibre and reduce its performance in commercial products.
For the time being, hurd originated from combined stalks are also accepted by processors because of very limited availability of designated fibre cultivars. As the fibre industry matures, a premium price will be obtained for hemp managed for a specific application.
Bast fibre buyers’, other than for textiles, (i.e., for biocomposites, insulation, etc.) uses do not always require hemp to be cut at the commencement of flowering. For their applications, lignified stems derived from hemp grown for the grain often deliver sufficient fibre performance. Unless specified by the end fibre user, retting may not be absolutely necessary.