If there are any general similarities or common ground between the two target markets you can accomplish this goal with a single blog using target market-specific keywords and category names.
I have a client who is in the home improvement industry, installing replacement roofs, siding, windows, doors, etc. People who need a new roof for example, more often search with keywords and phrases focused on their specific need rather than something general like home improvement contractor.
We use recently completed projects as the fodder for content-based marketing. Blog posts include the town and/or neighborhood, county and state where the work was performed for geo-targeted keywords. We then include a generous sprinkling of "roof," "new roof," etc. along with product-specific words like the type and brand of shingles installed.
We also include a description of the initial problem the homeowner was experiencing that caused them to contact us initially, such as "leaking" or "leaky roof." We do the same thing with all of his other product areas and get a great deal of traffic.
One last trick is to use many of these same keywords as blog categories. I have seen great success with this tactic.
If what I've described makes sense to you and you'd like to learn more, please click "Call Frank" below so we can discuss further.
To your success, Frank