Ideally you should be buying stocks for your portfolio with the idea in mind that you will own them forever. While few, if any, investors actually do that, the purpose of the exercise is to create a mindset that differentiates you from the day trader, who's constantly flitting in and out of positions.

As the investing saying goes, your portfolio returns are not based on market timing, but rather by time in the market. It's why buy-and-hold investors are far more successful than those who are always buying and selling shares.

While any stock you purchase should be held for a minimum of three to five years, the three stocks below are ones you can comfortably own for the next 20 years and not worry about.

Person checking stock charts.

Image source: Getty Images.

1. ABM Industries

Janitorial services and facilities manager ABM Industries (NYSE:ABM) is in an industry so boring you probably just fell asleep reading that sentence. Yet it's the ho-hum nature of ABM's business that makes it an easy call to be a long-term hold in your portfolio.

ABM has been around for 112 years, meaning its been through two world wars, the Great Depression, the Tech Wreck of 2000, the War on Terror, the Great Recession, and the pandemic. To say it's survived more than a few upheavals and continues to thrive would be an understatement.

Particularly after the COVID-19 outbreak, and now with the spread of variants of the coronavirus globally, there's a heightened need for cleanliness and sanitation. ABM has developed stringent cleaning protocols, which it calls EnhancedClean jobs, that helped it to more than double adjusted operating profits last year. 

That's undoubtedly going to be a driver for future growth for some time to come, but even when the world returns to normalcy, its services will be in demand. Coupled with a dividend it has paid for 56 years -- and raised annually for the past 50 years, making its stock a Dividend King -- ABM Industries is a company you can set and forget in your portfolio.

Doctors using robotic surgery system.

Image source: Intuitive Surgical.

2. Intuitive Surgical

Robotic-assisted surgical systems are certainly much sexier than janitorial services; and Intuitive Surgical (NASDAQ:ISRG) is a stock you can own for the next two decades because it is at the leading edge of the industry that will be the future of how surgery is conducted, if that future isn't already here.

Intuitive Surgical is running so far ahead, its competitors aren't even close. It has installed well over 6,300 of its da Vinci systems that assist doctors in performing minimally invasive laparoscopic soft tissue procedures. Their accuracy leads to smaller visible scars after surgery and faster patient recovery times. The ubiquity in hospitals and surgical centers around the globe -- all of the competition's machines combined don't add up to half of Intuitive Surgical's installed base -- gives it something approaching monopoly status in the industry (which has admittedly led to some lawsuits).

There is future growth opportunity deriving from Intuitive Surgical's ability to continually expand the da Vinci's addressable market to other surgical procedures, such as thoracic, gynecological, urological, and general surgical practice where it has added wrist stapling capabilities. Look for this leading surgical assistant to keep leading the field.

Technician testing marijuana.

Image source: Getty Images.

3. Jushi Holdings

Marijuana is another area with massive potential, even if the results in the space have been less than spectacular so far. Some 36 U.S. states have legalized medical marijuana use so far, and another 18 allow marijuana to be sold for adult usage.

Taxes and regulations have been two of the biggest hangovers confronting the industry, but Jushi Holdings (OTC:JUSHF) just might be able to circumnavigate these hazards better than others because of its narrow focus.

The multi-state operator currently targets growth in just three core states, but it's looking to expand to new markets with selective acquisitions, such as its recent purchase of Nature's Remedy in Massachusetts. It's opening 10 to 12 new stores this year, which will give it as many as 27 by the end of the year, and Jushi intends to grow its cultivation assets from three states to five states.

Jushi is an exciting opportunity because it is a stock offering investors high rates of growth today. Over the coming decades as the cannabis industry matures in the U.S., it should be one of its leading lights that will also provide stable returns in the future as its base of operations spreads. 

It's a riskier investment than either ABM Industries or Intuitive Surgical, but should be one investors can readily own for the next 20 years and beyond.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.