The science behind growing your own cannabis

CATHY WURZER: Here's the other story you're going to hear a lot about. Tomorrow, Minnesotans will legally be able to grow, possess, and use marijuana, but it will still be a while until people can buy weed in most of the state. We're about a year away from having licensed dealers in the state.

Instead, tomorrow, the Red Lake Nation will sell recreational cannabis from its dispensary. The White Earth Tribe is expected to follow. Also starting tomorrow, Minnesotans 21 and older will be able to grow up to eight cannabis plants at a time. NPR News reporter Mark Zdechlik spoke with one man getting his indoor grow tent ready for August 1.

TYLER: My name is Tyler. I'm 32 years old. Marijuana has been around my entire life for myself and my friends, and it's just been an alternative to alcohol. This is called a grow tent. Mine's 4 foot by 4 foot. I've got four buckets in there getting ready for the grow. And I'm ready for August 1.

CATHY WURZER: Which is tomorrow. Tyler says he hopes to have his first harvest by November. He's one of the Minnesotans around the state getting ready to grow for the first time. Peter Morrell is on the line right now.

He is a professor in the Department of Agronomy and Plant Genetics in the College of Food, Agricultural, and Natural Resources Sciences at the University of Minnesota. He teaches a class each fall on the science of marijuana. Welcome, Professor.

PETER MORRELL: Thank you.

CATHY WURZER: I don't know if you followed the debate at the legislature on legalizing marijuana. It is pharmacologically complex as a plant. Do you think policymakers understand the science to make good decisions about its use?

PETER MORRELL: I'm not sure if the legislature has understood all the subtleties. Based on the guest speakers we've had in my class, I think the state regulatory agencies have had really good conversations about how to manage both hemp and medical marijuana in Minnesota.

CATHY WURZER: And for folks who are a little confused, remind us what makes legalized cannabis different from the already-legal hemp products.

PETER MORRELL: So hemp products have been federally legal for a number of years. And hemp is defined as a cannabis plant that has delta-9 THC below 0.3%. Hemp has traditionally been grown for fiber and that sort of usage, but there has been recently hemp that is primarily drug-type cannabis used to grow CBD.

But marijuana has a much higher concentration of THC. Otherwise, there's no real difference in hemp and marijuana. They're both Cannabis sativa.

CATHY WURZER: Potency is a big issue, right? How has that changed over time?

PETER MORRELL: It's increased a lot, especially if you go back to comparing to, say, the 1950s when a lot of Americans had their first exposure to cannabis. But it's gone from a few percentage points to-- I think I saw today 15% is the average now. And cannabis where the dried flower is 30% or more delta-9 THC is not unknown.

CATHY WURZER: 30% or more? Wow, that's a lot.

PETER MORRELL: It is.

CATHY WURZER: Let's talk about growing right now. Cannabis obviously goes by the nickname weed, right? Is that any indication of how easy it might be to grow?

PETER MORRELL: Yes and no. I mean, feral cannabis plants are pretty widespread in Minnesota. And so cannabis can grow in a ditch or in a field. But actually growing marijuana in a way that's going to produce buds that are usable for-- for drug use, cannabis requires a fair bit of tending of the plants.

So you can't simply cast some seed out and water them occasionally. They're going to require the same kind of management that most things would in your garden, at the very least.

CATHY WURZER: And of course, the wild cannabis, I would presume, the potency isn't all that great-- or isn't all that high?

PETER MORRELL: It's pretty low. There's been some research from a couple of folks at the University of Minnesota that's shown that it varies quite a bit, but most of it will-- smoking it, for the most part, will give you a headache and nothing more.

CATHY WURZER: OK. I am no plant expert here, but I know that there are regular seeds which produce both female and male plants, right? What are feminized seeds?

PETER MORRELL: Feminized seeds are-- and I need to make sure I get this right. But they are intended to produce only female plants. So the highest-quality marijuana is sinsemilla, or Spanish for without seeds.

And so you actually don't want the flowers to be pollinated. So ideally, when you get a batch of feminized seed, all of the seed has been turned into female plants. Cannabis has X and Y chromosome sex determination, a lot like humans.

So there's been a genetic change made so that all of the plants will only produce female flowers. And so all the plants will be female or only produce female flowers.

CATHY WURZER: So you can cut out the guesswork from the budding thing, right?

PETER MORRELL: Yeah. It will reduce the chance that the plant gets pollinated and then said seed. It will be a real problem for people growing cannabis outdoors. Depending on where you're growing it, that cannabis pollen can travel quite some distance, so plants could easily be pollinated by plants nearby. The pollen is windborne and it can travel quite some distance.

CATHY WURZER: You teach this class in the science of marijuana every fall, I understand. What are some of the more common challenges that face potential growers?

PETER MORRELL: So to date, of course, no one has legally grown marijuana in Minnesota other than for medical use. It's a couple of companies that have contracted with the state to do that through Minnesota's medical marijuana system. I would say, the biggest challenge for growers has been the market for some of the products.

We have some very active growers in Minnesota who've been really aggressive about finding their own pathway to market for their hemp products, but it's certainly a challenge. For example, there's considerable potential to make fiber out of hemp, but getting that to market and finding someone who can accept it and process it has been a real issue.

CATHY WURZER: Hmm. OK, so there's the distribution in the market, obviously. And going back to growing for just a moment if I could, you mentioned that you just can't stick the plants in the ground. You have to do some work, right? Are marijuana plants finicky in that regard in terms of what they need?

PETER MORRELL: Their growth requirements are not dissimilar to corn or maize. They like nitrogen. They can be relatively big plants, so they need a fair bit of space to grow.

Marijuana plants tend to be shorter and bushier, whereas hemp plants-- this is speaking very broadly-- tend to be taller and thinner. But they do require nitrogen fertilizer. They like relatively wet soil, but it needs to drain reasonably well. So not terribly different than growing, I guess, sweet corn in your garden in that regard.

CATHY WURZER: Mm-hmm. What are the things you're going to be looking-- you're an expert in the field here, and you're very familiar with this plant species. What are you going to be most curious about here in the coming days, weeks, and months when it comes to folks that are going to start to grow at home?

PETER MORRELL: The part that I don't quite understand yet is where home growers are going to source their seed. Marijuana seed is only quasi legal in the sense that it's been legalized in the state, but you can't transport marijuana seed legally between states. So I'm not exactly sure how you get the market started here.

Where does that seed come from that the growers initially use? So I'm pretty interested in-- and if you do a search online today for marijuana seed in Minnesota, you don't immediately find a lot of legitimate vendors or legitimate-looking vendors. So I'll be interested in seeing how that market develops.

CATHY WURZER: And as a person who is a professor, will you be looking forward to any research that may occur because of this new market that we have?

PETER MORRELL: George Weiblen at the University of Minnesota has been involved in cannabis research for a number of years. My own lab, I have not been involved in cannabis research mostly because there haven't been clear state, federal funding streams to support cannabis research. There is a little bit of money now from the USDA to support hemp agronomic research, but I don't think it'll be a major push in my lab's research.

CATHY WURZER: Mm-hmm. What questions, though, do you think need to be answered when it comes to research?

PETER MORRELL: There are questions that are outside my realm of expertise. But there are legitimate concerns, I think, about how people successfully grow marijuana at home in a sustainable way. There's a lot of energy use around cannabis production.

You had the little lead-in with the story with Tyler, and I saw the photographs of the home grow setup he has set up. It looks pretty looks pretty nice, but it looks expensive. But trying to maintain an environment that is warm enough, with enough light, with enough humidity or low-enough humidity, depending on the time of year to grow, and enough air circulation to grow marijuana primarily indoors in Minnesota is going to be a challenge. And how we encourage the sustainable development of that kind of activity will be quite interesting, I think.

CATHY WURZER: All right. Interesting conversation. Thank you so much for your time.

PETER MORRELL: Yes, thank you.

CATHY WURZER: Peter Murrell is a University of Minnesota professor in the Department of Agronomy and Plant Genetics in the College of Food, Agricultural, and Natural Resource Sciences.