How to Feminize Cannabis

By: Soft Secrets, March 5, 2019

the DHSC explain how they utilize the STS method (Silver Thiosulfate) to produce feminized Cannabis genetics, why they do it and how their genetics are received around the world.

In issue #3 of SSUSA, we introduced you to the Devil’s Harvest Seed Company, relatively new faces on the Amsterdam seed scene. They were generous enough to share their company secrets and explain how they got started. In this issue, the DHSC explain how they utilize the STS method (Silver Thiosulfate) to produce feminized Cannabis genetics, why they do it and how their genetics are received around the world.


Feminized strains are a hot topic of debate in the Cannabis industry. Some argue that they’re the best thing to happen to both small growers and those with huge plots of land to cover; others fear that they may be creating ‘zombie weed’ due to their unnatural origin. So what makes a seed company decide to take the leap into the feminized realm? For the DHSC, it was the seemingly overnight demand for and rampant popularity of these ‘all-female’ seeds. That, however, was not the only reason. One half of the company explains:

“I started with feminized in my early days of growing, so I know why people who are just starting need feminized seeds: lack of space; new flavors every few months, rather than the same, boring flavor for the next 12 months. Outdoor growers get the benefit of maximized space; for indoor growers, the benefit is not having to keep a collection of mothers and clones – and constant storage. Also, they don’t have to maintain a library, which is fucking hard.

“The third reason: just because it was a new thing that everyone thought would solve all their problems. But you realize when growing with feminized that they don’t help you to develop your skills; it just allows you to grow something once, and to recreate something new every three months.”

The plants are triggered into flower and sprayed several times. After a few weeks, the flowers/hermies begin to show, seen here in the Strawberry Sour Diesel.

While checking out a variety of feminization techniques, the DHSC found that, “through trial and error, the STS method seems to be the most successful one in the industry, and from talking to many people who make feminized seeds, it appears to be the favorite. It seems to be the most reliable; it works, simple as that.” STS is a compound often found in photography labs, the silver in which ‘locks out’ the copper in plants. Because copper is a required micronutrient, inhibiting it causes ‘ethylene signaling’, which will repress certain traits, such as gender expression.


“We select between four and six plants, and we take them from a vegetative state into the flowering cycle. When we trigger them under 12 hours of light, we spray them while they’re in their dark period with a heavy dose of STS formula. Basically, five milliliters to every one liter of distilled water. When they’re sprayed, we give them a 15-minute break period, then we spray them again – typically over six plants, we’ll use about four liters of distilled water (with STS formula mixed in). It’s kept refrigerated.

Pre-vegged female clones are introduced to the hermaphrodite/sprayed plants. Later, when pollen is released, the pre-flowering females are impregnated, making feminized seeds.

“Then, once we spray, we allow the hormones to trigger, and the onset of flowering will begin. Five to six days afterward (depending on the strain and the quickness of flower) we spray it again with about three-and-a-half to four liters of distilled water mixed with STS formula. Fifteen minute break, and then we spray them again with the same dosage. Then, seven days from that point, we spray them a third time with a very heavy dosage, and we’ll use up to six liters of a mixed STS formula. On that three-week period, the plants have fully-induced into flower, and then we begin to see the onset of hermaphrodites starting to occur.

“From that point we take female clones that have already been pre-vegged, and we take them into the room and introduce them to the hermaphrodite/sprayed plants. When the release of pollen occurs, in another two weeks – so that would be five weeks of the hermaphrodite plants flowering – they release pollen, and the new female plants that have just started their pre-flower accept that pollen and, thus, make feminized seeds.

“We remove the STS-sprayed plants after seven weeks of flowering, and we allow the female plants to finish their flowering period with plenty of breathing room, too. So, that’s how we do it. It’s complicated, but it works; and it’s all about timing.”

Genetics are not the only concern: the quality of a person’s grow room helps to insure either success or failure, depending on the efforts of the grower. This will also affect the quality of seeds. In computer terms: garbage in; garbage out. For this reason the DHSC attempts to produce their seeds carefully and in good conditions.

Usually, males and hermies are plants that one would avoid having in one’s grow room.

“We provide [our seeds] to certain growers to test, and they test them for us straight away; they grow them out and each grower will give us feedback.”

“We’re using an organic mix, a soil and worm casting mix with good nutrients, because we want to provide good seeds. We use grow tents. We use 600w HPS lights; we use what works. Until they come up with a new invention we won’t use anything else. LEDs just don’t work: this is seed production. We treat it as though we were flowering the weed. Giving it everything we can, providing everything that’s good for it: all of the best nutrients we can, the best medium. We don’t do it for flavor, but we provide it with some guanos and some of these basic, organic composts to allow it to naturally grow, to give you a harder, solid shell on your seed. It’s about giving you really good seeds that will last long-term in storage.

“One 600w HPS is used over each meter, and we grow typically between 12 and 20 plants in six- to eleven liter pots, depending on what we’re doing and how big the plants are. We don’t use RO water because we don’t stay in these places too long; we don’t want to have leaks and we don’t trust taps and stoppers and all that. It just isn’t 100% safe for us; it’s more about safety than anything. The water in Amsterdam is really good anyway – I think if you look up tap waters around the world, Amsterdam is known for having a really good source of tap water.

“Our seeds are stored at room temperature for preservation; we believe that if you want to store your seeds in the refrigerator for long-term, that’s your choice as a customer. For us, as seed producers, we keep them at room temperature and when you get them it’s up to you to wake up the seeds. When you put them in storage for long periods you can put them in the fridge, but we don’t do that because if we refrigerate them and there’s a power outage, we lose our entire batch of seeds.

“We also know from experience that it’s better to store them at room temperature in a cool, dry, dark place, for three to five years if in an air-tight container. Basically, if you want to do refrigerated storage that’s your decision; but it isn’t recommended for us to do it because of the large volume we have.”


Careful selection of truly female clones will help to guarantee success in the seed-making process.

Hermies are removed to allow the females space to finish flowering.

Mixed-gender plants can ruin entire grow rooms. So how do the DHSC combat hermaphroditism? “By selection of good clones that originally have been around here so long – long before feminized seeds – and they were grown from original genetics, so we know 100% that they aren’t selected clones from a feminized plant (these are real mother plants with no [hermaphrodite] traits existent in them already). So we hope from that, with our feminized technique, that we won’t cause hermaphrodites.

“We’re not saying it’s 100% until we test. And even when we do test we still don’t know, out of all the thousands of seeds, if any one of them will produce a hermaphrodite. So we’re trying to provide the market with what the demand is.” The testing process is mandatory for any seed producer wishing to survive in this industry.

“As soon as we make seeds, we dry them out and we grow them in the pre-flower. We provide them to certain growers to test, and they test them for us straight away; they grow them out and each grower will give us feedback. And on that, we stress them (in one room, as a basic grow setup) with light leaks, with spraying them and leaving them out exposed to 24 hours of light while they should be in flower; we give them all the stresses to cause an onset of hermaphroditism, to see if any will turn. If any do, then they’ve got traits in there that we don’t like to find.

“Some of the genetics that we have aren’t suited to be feminized because they do have hermaphrodite traits, but it’s because of the popularity of the strain; it’s the only way we can bring it to seed. We hope that the hermaphrodites are a very minimal problem.”

Top 5 Countries That Produce The Best Weed


Hermaphrodites are one issue, potentially causing the loss of the rent payment for months to come, as well as potentially contaminating your growing/flowering space. However, the health concerns associated with the production of feminized seeds should be more worrying. A question that frequently arises when debating the matter is whether people or the plants themselves are harmed as a result. The DHSC warns: “It’s definitely dangerous to your own health, because that stuff, it’s the same as in rocket launchers, and when you breathe it in…. The silver that’s exposed, when the troops inhale it, they were coming up with all these sicknesses, so the Army have records of people breathing this stuff in (the silver thiosulfate). This is the guys standing next to the rocket launchers all day, who ended up with Veteran’s Disease.

“You have to remember that these are serious chemicals – you must be a licensed company to buy these chemicals. You have to know what you’re doing„

“It is definitely not good for our health, so we wear breathing masks and rubber gloves, and goggles, plus a full coverall suit. It’s all about safety. If the spray gets on your hands, it leaves rusty-colored spots on your skin that can stay there for a couple of days; or, it can bleach your skin. You have to remember that these are serious chemicals – you must be a licensed company to buy these chemicals. You have to know what you’re doing. It’s not for amateurs and it’s definitely not to be left around for kids to play with.”

That’s probably sound advice regarding much of the things one would find in a grow room. However, the exposure doesn’t end there. What happens to the sprayed buds? Don’t many people secretly sell them off or smoke them anyway, despite knowing it’s a contaminated product? Not the DHSC: “I don’t use that stuff afterward. I think it’s too dangerous to give to people because we have sprayed it with silver. The ingestion of silver through smoking, I don’t think it’s good for anyone.”

After two- to four weeks of drying, the seeds should be safe, as the two remind us. “It won’t, however be in the seeds any more, once they’ve dried out. You’re at no risk at this stage. But it’s the production process that’s a dangerous step – there are dangers that just aren’t good for your health. So, we do take precautions against things like that, but that doesn’t mean that everyone in the industry is being so careful. We’re trying to do this as correctly and safely as possible; but other people are doing it just to make money and just spraying every plant; they’re using those seeds to sell and telling you that they’re feminized. They are really good looking-seeds, but they’re not feminized.”


“The DHSC is going fully-feminized this year, so we’re trying to bring every available clone that is popular in Amsterdam, and release it with the feminized label.” When choosing strains for feminization, the DHSC have one simple criterion: they select what they like to smoke. “When we find something that is ‘our’ flavor – and our flavor is our flavor; it doesn’t mean it’s everyone’s flavor – we go with it. That’s what gets our interest going, is something with a really good flavor. It doesn’t really matter to us about the yield or how it’s grown; number one is the flavor. After that we get to know the strains and how difficult they can be.”

“The North Americans are still into the old way of doing it, and they’re keeping the genetics alive much more than we are over here„

The company’s tendency to produce heavy-hitting, interesting varieties in regular- and feminized versions is no accident. Part of the key to their success is keeping an eye on the international market and understanding the differing needs of growers around the world. The two explain that “the American market is still open to regular [non-feminized] seeds, more so than the European market. That’s a really good thing. The North Americans are still into the old way of doing it, and they’re keeping the genetics alive much more than we are over here. They do more groundwork.

“At the moment, the major difference between some American growers and us in Europe is that they’re doing it legally and we’re doing it illegally. It’s not legal for us to do it here; it’s very difficult for us to resource everything. Even though you may think it’s legal in the Netherlands, it’s not and it’s in fact frowned upon – very hard for us to do. But we love doing what we do and that’s why we keep doing it. If we had a legal way of doing it, we’d be able to do it even better. So, even though we’re restricted with our resources here in Amsterdam, we still provide as well as we possibly can. That defines us: we’re restricted in such a way that some of America has more freedom than we do right now. But that can change very fast.

“Canadians kind of learned their old school growing from the Dutch. Typically, the Canadian growing style is very similar to ours over here. And again, they’re more legal in Canada than they are in the US. They can do things there that we can’t over here, but I think it all comes back to Amsterdam. No matter where weed goes in the world, this is where it started and this is where it ends. Being an Amsterdam seed company helps to set us apart: ‘they’ are there, and we are here. We have our genetics that North Americans crave for over there, and we’re trying to bring it to them. We’re also trying to get genetics from over there and bring them to people over here. The demand goes both ways.”

Although they’re a relatively new company, but the DHSC varieties are definitely recognizable around town. The lads suggest keeping an eye out for their Shoreline. “We’re crossing it with everything we have right now. But we’re also working on making S1 seeds with it, ’cause it’s an original genetic. There’s no parentage left for it to breed any more, so we have to make S1s to keep the original genetic alive, but we’re also going to make crosses of it to preserve the genetic.”

A ‘pregnant’ female flower

The DHSC are feminizing all of their favorite clones from the smoke industry in Amsterdam, such as this Super Silver Haze.

Currently, the DHSC enjoys a primarily European customer-base. However, they hope to change this soon. “We’re aiming towards America and Canada, but due to legal reasons we cannot directly sell there at present. In the future we aim to make [our seeds] available to North Americans as much as they’re making their strains available to us.” It’s this kind of open market that will help to ensure that certain, beloved strains don’t become extinct, especially with all the genetic experimentation going on these days. The DHSC have proven that they can adapt to the ever-changing demands of the Cannabis industry. A willingness to pursue new customers in new regions also helps to keep growers interested.

“At the moment, we’re so new that we haven’t even found the region that is most popular for outdoor growing with our seeds. It’s mainly based for indoor growing; we haven’t tested them in outdoor regions enough to know the results of where they are best suited.”

So, what does the future hold for DHSC? “A million dollars [big stoner laugh; he tells me to just print ‘$$$$’] Retirement! To keep developing and looking for new strains and to outsource strains in different countries.

“We need to go backwards to go forwards. We’re currently researching into old-school genetics and old strains, rather than going for the hype of the new ones that are available now. We are looking into older generations. The older, the better. The more of a challenge it becomes, the more fun it is, and the more interesting it can be. Otherwise, it would only end for us. We need to keep it going.”

Photos by DHSC

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