Want to be kind to the planet and your portfolio at the same time? The Fool shows you how in our special series on Earth-friendly investing.

If you care about protecting our planet from humanity's harmful effects, there's no limit to the ways you can get involved -- right down to your investment portfolio. Abundant mutual funds will help you invest in responsible ways, avoiding companies with potentially harmful environmental policies. Grab your hacky sack, and let's take a look at some of these "green" funds.

Sierra Club funds
The Sierra Club may be the first group that springs to mind when anyone mentions the environment. Now the venerable organization offers its own brand of mutual funds, designed to invest only in companies that meet its social and environmental guidelines. The group's two funds, Sierra Club Stock and Sierra Club Equity Income, are both run by San Francisco's Forward Management.

The Sierra Club Stock fund is a large-cap growth offering, sporting such top holdings as Alltel (NYSE:AT), Boston Scientific (NYSE:BSX), and CVS (NYSE:CVS). While the fund isn't terrible, it does have rather high turnover at 129%, and it's only beaten the S&P 500 in three of the past eight years. That's enough to give me pause -- not to mention that the fund's current management team only dates back to January 2003.

Likewise, the Equity Income fund, which invests in both stocks and bonds, has posted less-than-impressive performance since its 2003 inception. In fact, the fund failed to beat an 80%/20% S&P 500/Lehman Aggregate Bond blended benchmark in 2004, 2005, and 2006. My verdict? Skip these funds, and make a donation to your local Sierra Club chapter instead.

Portfolio 21
If you're interested in a more global view of going green, Portfolio 21 might be the fund for you. Portfolio 21 is managed by Progressive Investment Management, which has specialized in social and environmental investing for 25 years. Portfolio 21 seeks to invest in companies that design environmentally friendly products, use renewable energy sources, and develop efficient production methods. Currently, the fund holds roughly 65% of assets in non-U.S. stocks, and it boasts a remarkably low 4% annual turnover. Performance here has been favorable, with the fund posting a 7.4% annualized return from its October 1999 inception through the end of March 2007, compared to a 5% return for the MSCI World Index.

The management team dates back to the fund's inception, it and appears to be doing a fine job of investing fund assets in ecologically friendly companies such as United Natural Foods (NASDAQ:UNFI) and Bristol-Myers Squibb (NYSE:BMY). All in all, Portfolio 21 is a great choice for a global environmentally focused mutual fund.

Calvert Large Cap Growth
If you're willing to entertain a socially conscious fund with a little bit more of a social "reach" than just the environment, consider some of Calvert's funds. Its approach to socially responsible investing includes screening companies based on seven factors, including governance and ethics, workplace, environment, workplace safety and impact, international operations and human rights, indigenous peoples' rights, and community relations.

One of its better funds is the Calvert Large Cap Growth Fund. Investors should keep in mind that this is a true growth-oriented fund, and it will lag the broader market in more value-oriented years such as 2000 or 2001. The fund also stumbled badly in 2006, hurt by positions in the information technology and energy sectors, but the longer-term performance picture remains bright.

The fund's manager, John Montgomery, employs a quantitative process to identify attractive investment opportunities that also meet Calvert's social criteria. The fund does have a healthy slug of mid-cap stocks (about 23%), and it tends to throw in a few international names as well. Expenses are a little high here (1.52% on the A shares), but if you're in the market for a socially screened domestic large-growth fund, give this Calvert fund a shot.

Of course, there are many more options available for those interested in ecologically minded investing. Just make sure to do your due diligence on each fund candidate before you buy, just as you would with any other fund. That way, you can rest easy knowing your investment portfolio is doing its part to support and maintain the environment, just like you.

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Fool contributor Amanda Kish lives in Rochester, N.Y., and does not own shares of any of the companies mentioned herein. The Fool has a disclosure policy.