For the past two years, I have picked out one company every month that I would be putting my own Roth IRA money behind. So far, those picks have returned over 19%, and they are beating the S&P 500 by just over 3 percentage points.

This month, however, I'm breaking form and buying three stocks for my Roth, as my recent sale of Lumber Liquidators -- which returned 250% -- has freed up more cash to invest. Read below to see which three stocks to buy this July, and at the end, I'll offer up access to a special free report on how to maximize your retirement savings.

Nuverra Environmental Solutions (NESC)
Until recently, Nuverra used to be known as Heckmann, but the goal of the company remains the same: to meet all of the water needs of North America's energy industry. Over the past few years, Nuverra has built out an impressive network of pipes, injection wells, water treatment plants, and trucking fleets that help streamline water usage.

While the energy industry -- because it's based on the underlying value of its commodities -- can be fairly volatile, there's no denying Nuverra's momentum. The company increased revenue during the first quarter by 190%, and from 2010 to 2012, that revenue increased 381% per year. The company also let it be known that the years of heavy spending on infrastructure will soon be coming to an end as Nuverra leverages its assets.

With shares trading 25% lower now than they were three months ago, I'm going to be buying shares when Fool trading rules allow.

Stratasys (SSYS 0.61%)
Though there are more than just two players in the game, the emerging 3-D printing industry is dominated by heavyweights Stratasys and 3D Systems (DDD 2.80%). While Stratasys has focused primarily on making printers for industrial use -- and bolstered that focus with its earlier merger with Objet -- it is 3D Systems that has focused on consumer products.

But Stratasys made waves last month when it announced it was merging with consumer-facing 3-D printing company Makerbot. As fellow Fool Blake Bos pointed out recently, MakerBot's Replicator is considered the iPhone of 3-D printers -- the coolest player in the game.

While Stratasys is certainly expensive by most traditional measures, these latest moves lead me to think that today's market cap for Stratasys of just $3.3 billion will look tiny a decade from now.

LinkedIn (LNKD.DL)
I'll admit it, I would much rather have been buying shares of LinkedIn when it was around $160 earlier in June. But the market -- and I -- has no qualms about paying a premium for a company that could disrupt HR departments of companies worldwide.

During the first quarter of 2013, LinkedIn was able to grow its revenue by 73% through three different channels: one focused on helping businesses fill openings, one focused on premium individual memberships, and one focused on advertising.

LinkedIn is certainly expensive right now, but it was when I bought it back in February and October 2012 as well. Since then, shares are up 115% and 80%, respectively.

More choices to help you retire comfortably
In the end, this series for me is about building a portfolio to help my family retire comfortably. The Motley Fool's free report "
3 Stocks That Will Help You Retire Rich" names stocks that could help you build long-term wealth and retire well. I personally own two of the stocks, and they make up a combined 15% of my real-life holdings. Click here now to keep reading and find out which three stocks we're talking about.