Arjan Roskam: The King of Cannabis and the Empire He Built in Amsterdam

If you have spent any time in cannabis circles, you have heard the name. Arjan Roskam is the founder of Green House Seeds, the man behind 40-plus High Times Cannabis Cups, and the self-appointed "King of Cannabis" whose face has fronted enough magazine covers and YouTube videos to make him recognisable on sight in any grow room from Barcelona to Denver.

He is also one of the most contested figures in the industry. Depending on who you ask, he either preserved priceless landrace genetics from extinction or commodified them for marketing purposes. He either built the most influential seed bank of the modern era or took credit for breeding work other people did. Both versions have evidence behind them, and the truth probably sits somewhere in the middle.

This is the story of how he got there.

From Thailand to the Tolstraat

Roskam started growing exotic cannabis in 1985, working with seeds friends had brought back from Thailand, Nepal, and other parts of Southeast Asia. His timing was awkward. The Amsterdam coffeeshop scene was already established, but the growers supplying the shops cared about two things and two things only: short flowering times and big yields. Long-flowering sativas, the kind Roskam was obsessed with, were considered commercially unviable.

For years he tried to convince other coffeeshop owners to put his cannabis on their menus. They passed. The flavours were too unusual, the effects too cerebral, the flower times too long. So in 1992 he opened his own coffeeshop on the Tolstraat in Amsterdam and called it The Green House. If nobody else would sell his weed, he would sell it himself.

The bet paid off almost immediately. In 1993, one year after opening, Green House entered the High Times Cannabis Cup and won the overall prize on its first attempt. The next year, Roskam swept nearly every category in the same competition. By 1995 he was on the cover of High Times magazine, and the floodgates opened. Smokers from around the world started making pilgrimages to Tolstraat to try the cannabis the man on the magazine cover had bred.

Green House Seeds and the breeding factory

Green House Seeds the seed company was founded the same year as the coffeeshop, with Roskam as founder and co-owner alongside Scott Blakey, the Australian breeder better known as Shantibaba. Their working relationship was productive but short. Between 1997 and 1998 the two of them produced Super Silver Haze, which went on to win three consecutive Cannabis Cups and is still considered one of the best sativa hybrids ever bred.

Then they fell out. Shantibaba sold his share of Green House to Roskam in 1998 and went on to co-found Mr. Nice Seeds with Howard Marks. The split was bitter and the consequences are still being argued about in grower forums two decades later. The most contested piece of the split is the question of who actually bred White Widow, the strain that put Green House on the map. Roskam credits a former Green House worker named Ingemar. Shantibaba says he made it himself and took the original mother plants with him when he left. There is no neutral arbiter for this dispute and there probably never will be.

What is harder to dispute is what happened next. Roskam, now sole owner of Green House Seeds, turned the company into a trophy machine. Working with breeders like Franco Loja, who joined the team and became Green House's most beloved creative force until his death in 2017, the company developed an enormous catalogue of feminised seeds and racked up cup after cup at competitions across the world. Super Lemon Haze won the Cannabis Cup in both 2008 and 2009. Arjan's Haze #1 won in 2006. Hawaiian Snow, Great White Shark, Big Bang, El Niño, and a long list of others followed.

By the late 2000s Green House Seeds was the best-selling cannabis seed bank in the world.

Strain Hunters and the landrace question

In 2008, Roskam and Franco Loja launched Strain Hunters, a documentary series in which the team travelled to remote regions of Africa, Asia, and South America to collect and document landrace cannabis strains. The official mission was preservation. As Roskam explained it, landrace varieties had grown in their native regions for decades or centuries without crossbreeding, and they represented genetic information that would be lost forever if nobody bothered to collect it before commercial hybrid cannabis displaced them.

The films were beautifully shot and reached a huge audience. They also drew sharp criticism from a portion of the breeder community. Critics argued that Strain Hunters was less preservation work and more high-budget marketing dressed up as activism. Some pointed out that the team often paid local farmers for seeds and cuttings, then presented those acquisitions as personal discoveries. Others noted that of all the rare landraces Roskam claimed to have found over the years, very few of them ever made it into the Green House catalogue as commercial releases.

The criticism is fair, but it is also incomplete. Whatever the marketing wrapper around it, the Strain Hunters footage is the most extensive video record of landrace cannabis cultivation in remote regions that exists anywhere. Twenty years from now, when those landraces have likely vanished entirely from their original habitats, the footage will probably matter more than the controversy around how it was obtained.

The criticism, and what it gets right

The case against Arjan, condensed, goes like this. He is a brander first and a breeder second. He took credit for work that other people did. He commodified landrace genetics under the cover of preservation rhetoric. He sold derivative cuts as original genetics after the Shantibaba split, and the quality difference between Green House White Widow and Mr. Nice White Widow is the proof. He paid off Cannabis Cup judges. He is, as one critic put it, the P.T. Barnum of cannabis.

Some of this is provable. Some of it is hearsay that has hardened into accepted fact through repetition. But even the parts that are clearly true do not quite cancel out the rest of the picture. Roskam built coffeeshops that put exotic sativa genetics in front of millions of people who would never have encountered them otherwise. He turned cannabis breeding into a profession that could support a family. He used his celebrity to push for legalisation in countries where pushing for legalisation could get you arrested. The Strain Hunters series, marketing or not, introduced an entire generation of growers to the concept of landrace genetics and why they matter.

You can hold the criticisms and the achievements in your head at the same time. Most of the people who have actually worked in the industry for a long time do.

The man at sixty

Roskam is in his sixties now and shows no signs of slowing down. He still appears at industry events, still gives interviews, still releases new strains under the Green House label, and still talks about the future of cannabis with the same mix of bravado and weary realism he has been deploying for thirty years. At Spannabis Barcelona in 2025 he told an interviewer that not a single country has legalised cannabis correctly so far, and he was probably right.

His empire today includes four coffeeshops, two clubs, the seed company, a nutrient line, a documentary production house, a foundation, and a medical cannabis arm. By any reasonable measure he has won. The King of Cannabis title was always self-appointed, but at this point, decades into the project, nobody else is really competing for it.

Whether you think he earned the crown or branded his way into it, he is wearing it. And the strains he and his team built are still being grown in tents and gardens and grow rooms all over the world, decades after they first hit the catalogue.

Where to start with Green House genetics

If you want to taste what the fuss is about, the obvious starting point is White Widow, the strain that made Green House famous in the first place and still earns its slot on Amsterdam menus three decades later. From there, work your way through the haze family, the Arjan-named cuts, and the cup winners.

The cannabis world is full of bigger personalities and louder claims now. Roskam built his empire when there were almost none. Whatever else you think of him, that part of the story is true.