04 Feb Autoflower Hemp 101 Webinar, Part 2 Questions and Answers
As with Part 1, we closed Part 2 of HiLo’s Autoflower Hemp 101 webinar with a live Q&A session. Scott Knippelmeir of Agrarian Supply covered the following autoflower hemp farming questions from the audience.
How many plants should we plant per acre?
Autoflower will have a size restriction that is unrelated to the date of planting because it matures on a days-to-maturity schedule. For Autoflower, the recommendation is to plant anywhere between 10 and 20,000 plants per acre. There are several reasons for such a wide scale. For example, if you’re trying to extend your season by planting early or late, the plants are going to be smaller and you’re going to need more plants per acre to cover your acre. In addition, if you’re on some sort of marginal ground where you know you have some restrictions about quality, you may need to plant more plants per acre to fill that space.
With photoperiodic plants, on the other hand, the plant size is directly related to the time of year you plant. For example, a plant you put in May 1st is going to finish its reproductive cycle October 1st. A plant that you put in June 1st is also going to finish October 1st. A plant you put in July 1st is also going to end October 1st. Photoperiodic plants are going to be successively smaller the later you plant them and–depending on when and how you plant–you can fill in all of your farm block area with as few as 1200 plants per acre or as many as 8000 plants per acre if you’re planting later in the season.
The earlier you plant photoperiodic plants, the bigger those plants are going to be—and they become a huge pain to deal with at harvest. You end up with a lot more lignified stem material that–unless you’re growing for fiber—you aren’t getting paid for. For these reasons, I’m a big fan of small plants.
I think that even though the upfront cost of seed and transplants can be a little bit off-putting sometimes, large plants are almost impossible to deal with at harvest in any kind of efficient, mechanized way. Furthermore, when you have your plants spaced out early in the spring on really wide spacing, you have a lot of time to let weeds come up in those open spaces.
How do I know how much compost to use?
It depends on the quality of the compost. As long as the compost doesn’t have too high of a salt index, you can put up to 20 to 40 tons of compost on per acre. A lot of times, though, you can’t afford to do that. A nice target number is five to 10 tons of compost per acre, which gives you a nice amount of nitrogen and helps build up your soil microorganisms (kind of bank in the soil).
Can I add gypsum to raise my pH?
No. Gypsum does not raise the pH. It acts as a neutral in the soil. When gypsum separates, it separates into a calcium ion and sulfate ion. Calcium is positive and would raise the pH, but the sulfate will lower the pH – so the effect neutralizes itself. Gypsum is good for adding calcium to the soil, but it will not raise the pH.
Can I spread all my amendments at the beginning of the season?
It depends on your yield goal for the season, the release rate of the nutrients, and the type of soil you’re on. Check with your agronomist.
I usually just sift the soil to prepare for planting? What's the deal with ripping?
With ripping, or spading, there’s a deeper tillage. Hemp roots have a rooting depth of zero to 10 inches for the feeder roots, and zero to 30 inches for the structural and water roots. With a disc, you’re often limited to 6-ish inches of soil work, and the plant needs more than that to explore for the root zone.
Do different types of seeds need different nutrients?
Yes. Different varieties do have different nutrient needs, and we’re still learning a lot about those differences. More importantly, the size potential of the plants cause them to have different nutrient needs. Single, autoflower plants will have less total nutrient needs than a 10-foot tall photoperiodic variety.
What are your thoughts on using biochar as a soil amendment?
I think biochar is really interesting. You want to make sure that the biochar is high-quality biochar. It can have weird effects on the soil depending on how it was created and what the feed source was, so I would approach it with caution. Make sure that you have your pH stabilized. Some low-quality biochar can cause odd pH changes in the soil and lock up nitrogen–because you’re adding a big carbon sink. Depending on how much microbial activity you have in the soil, if you’ve got low nitrogen a lot of times those microbes eat first before the nitrogen is made available for the plant. So, I think biochar is fantastic but it needs to be used judicially and with caution.
Do you have a couple tips for boosting microbiology life?
Yes – compost, cover crops, and not overworking the soil. I didn’t get a chance to talk about cover crops, but microbes eat sugar and roots leak sugar. Sometimes up to 40% of a plant’s total photosynthates leak out the roots. So, keeping a cover crop that is leaking those sugary photosynthates into the soil will increase your microbial population, and then compost basically is microbial life. So, adding compost, keeping a cover crop, not destroying your soil structure by excessive soil working, and not pulverizing and mixing your soil layers.
Most microbes have a pretty small range that they live in the soil, so a microbe that lives at one centimeter often times can’t live at four centimeters, so you can imagine if you’re mixing and pulverizing your soil you’re creating more problems for those microbes to reestablish.
What is the footprint of autoflower on the surface at maturity diameter of the plant?
It can depend on the season and the soil type. The further north you go, the larger the potential for autoflower because (as opposed to a photoperiodic variety) it’s size limitation is often a function of the amount of light units, growing degrees, and solar radiation. At a very high latitude (e.g., Canada), you can have enormous autoflower plants when the days are 18 to 20+ hours of daylight.
For most areas in the continental United States you’re looking at somewhere between a 2 x 2 and 3.5 x 3.5, depending on the fertility of your soil, and whether you’re growing for a main season crop or a shoulder season. If you’re trying to grow an early autoflower crop so that you can either get to market early or follow up with another crop on the same ground, you should plan for a 2 x 2 space.
It’s hard to put too many down. For weed control, I like to put autoflowers pretty close to each other. When we’re direct seeding, I’ll have people direct seed 14 inches between seeds and line. Even though the plant might not have room to stretch out side to side, it helps for weed control in the seed row because they’ll close out earlier. It also helps the plants hold each other up.