This article is part of our Rising Star Portfolio series.

These are uncertain times for sure, even if many investors are enjoying the U.S. market's rally today. Continued eurozone strife drums up a great deal of uncertainty, and the U.S. fiscal situation isn't all that comforting, either.

Though I plan on letting the long term play out for the purchases I've made for the Rising Star portfolio I'm managing for Fool.com, I thought I'd outline five stocks that I believe are the safest in uncertain times. I know some investors want safer stocks in which to park their money, with a higher chance of continued growth even if the overall economy continues to be lackluster.

Five strong favorites
Every investor's appetite for risk is different. Many would rather avoid more speculative companies like biofuels start-up Solazyme (Nasdaq: SZYM) and solar contender First Solar (Nasdaq: FSLR). I'm holding on to both stocks, but Solazyme is down nearly 60% since my first purchase, and First Solar's plunged 66% since I bought in September.

If you're not sure you have the temperament to ride some major stock-price ups and downs with such risky stocks, here are five strong, more stable stocks to consider buying and holding in your portfolio (and why).

Costco (Nasdaq: COST): This well-managed warehouse retailer is a gold-standard stock. It treats employees well and enjoys strong customer loyalty. It also caters to an important part of the U.S. economic engine: small-business owners. Although its forward price-to-earnings ratio of 19 looks pricey compared to those of discount rivals like Wal-Mart and Target, don't be fooled: That premium price is the price one pays for a solid, strong long-term business. Costco pays a dividend, too; its trailing annual dividend yield was 1.2%.

Clean Harbors (NYSE: CLH): When companies like BP and ExxonMobil make a big, dangerous, oily mess, that's an opportunity for Clean Harbors. This company, which specializes in hazardous-material management services and environmental remediation, helped clean up the Gulf Coast after BP's Deepwater Horizon spill, and also racked up $42 million in connection to ExxonMobil's Yellowstone spill this past year.

Whole Foods Market (Nasdaq: WFM): This may look like one expensive grocery stock (it trades at 26 times forward earnings), but don't let the price drive you off. Whole Foods has achieved a successful year few anticipated, consistently growing sales despite a difficult economic environment that even challenged the mighty Wal-Mart. Long term, the organic grocer has big plans to grow its store base from just around 300 to 1,000 in the U.S. alone, and its emphasis on high-quality fare and educating consumers about healthy eating puts it on solid competitive footing. Whole Foods has a dividend yield of 0.8%.

Google (Nasdaq: GOOG): Google's a great defensive play for investors' portfolios. Its core Web search has infiltrated our daily lives, and the company's gaining traction in other important areas as well. Its Android smartphone operating system is giving Apple's iPhone a real run for the money in terms of users; in fact, research group NPD recently said Android smartphones comprise 53% of the smartphone market, versus 29% for Apple. (Granted, we'll have to keep a close eye on a current patent battle between Google and Apple in the smartphone space.)

One element that makes Google particularly bulletproof is its amazingly strong balance sheet; Google has more than $42.5 billion in cash (or $131 per share) on its balance sheet, and just $7.3 billion in debt. It's also dirt cheap relative to its growth prognosis, trading at just 14 times forward earnings and sporting a PEG ratio of just 0.89.

Waste Management (NYSE: WM): The fact that we all generate garbage isn't changing anytime soon, and Waste Management's bread and butter is hauling it away and disposing of it. However, Waste Management has truckloads of interesting green initiatives to transform trash into treasure; take its waste-to-energy subsidiaries and strategic investments in green start-ups. It's also making money off recycling, allowing reuse of essential commodities. Waste Management is also the biggest dividend payer of these five stocks, boasting a hefty trailing annual dividend yield of 4.4%.

Stocks for better sleep at night
I have amassed many compelling socially responsible stocks in my Rising Star portfolio that have wonderful potential despite short-term stock price drama. Those investors who'd rather take a walk on the tamer side of investing might want to particularly focus on the five stocks outlined above, though.

No stocks are risk-free, but some are riskier than others. These five stocks' staying power and competitive advantages should promise more conservative investors better rest at night.

If you're more interested in watching than buying these stocks for now, add them to your Watchlist to keep track of all the developments.