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Test your plants: starting the first couple weeks of flowering and get to know the rate at which the THC is increasing. Generally, in the last month it increases over double. If it was 0.2 THC on day 28 of flowering it would be 0.4 on day 56 and if you let it go another week or 2 it could increase up to 0.5. Seeding reduces resin production. Some experienced growers claim it does not lower THC much but decreases CBD production by 50% so you must still test early if you are seeding. The Department of agriculture demands you test 30 days before harvest. Don’t test a day late if you don’t want to risk losing your entire field. Every week test and watch the increase of THC levels carefully. Then schedule an appointment with the department of agriculture tester and make sure they are at your farm testing by the time your private tests reach 0.18 THC. By the time they dry the flowers the delta-9 THC level will rise perhaps 20-30% higher than when it was cut so take that into account. In Wisconsin farmers generally test the second or 3rd week of August. Then after you test you get to grow 1 more month and you can harvest your crop even if the THC rises above 0.3! If you wish to legally sell the extracts of those hemp flowers in some states, you must have the THC and CBD separated by a processing facility so that your products will not test over the federal limit. Other companies will straight up sell you CBD products with 1% THC in them without blinking an eye. As of lately there have been minimal legal problems in doing this though I have heard of drug task forces auditing CBD dispensaries on all of their products and lots of interstate shipping seizures. If you want to find a strain with the maximum CBD legally allowed, then search information about the THC:CBD ratios of the CBD hemp strains. 1:20 mean you could pull about 7% CBD by the time your plant reaches 0.3 THC while 1:40 would be about 14% CBD by the time it hits the legal limit of THC. Cherry Wine for example reaches 18.8% CBD while testing under 0.3% delta-9 THC. A very good ratio.
Harvest: Common practice is to harvest in the morning because a day of sunlight draws nutrients up into the buds causing the flowers to be harsher when smoked as well as other scientifically beneficial reasons. Also, it is good to flush your plants nutrients out with reverse osmosis water starting 3 weeks before you harvest. Water let the salts break down then water again 5 minutes later to flush out all these excess nutrients that may make your flower taste harsh.
Curing: Hang the plant or branches in the dark with sugar leaves removed and good air flow. Not too dry of air and not too wet, the slower the cure the better unless you are using dry ice method which takes only hours. After 1-3 weeks of hanging (depending on bud size) put in paper bags or breathable sacks for 3-5 months. Cannabinoid levels will rise another 20% or more when the stem pushes the last of its resin into the flowers.
Summary: CBD hemp flower sells by CBD percentage, so you want to test as late as possible while still ensuring you pass. $3.50 to $5 dollars per percentage point per pound is the current rate (March 2019). So, at 4 dollars per percentage point at 20% CBD flower would fetch 80 dollars per pound wholesale (outdoor grown). Greenhouse is higher quality and fetches a higher price, while indoor can be sold in retail settings for thousands of dollars per pound. If your outdoor is processed into end products the profitability can rise many times. Phenotypes (slightly different varieties in each strain) and grow conditions have a lot to do with the potency of cannabinoids and terpenes but generally the widely varied test results of each strain are because of this state mandated practice of testing 1 month before harvest while any right-minded grower tests his bud when it is fully dried (2 months later) to see accurate end results.