/diy/ - Do It Yourself

I want to make two of picrel and then connect them with a wooden grid so I can stake my tomatoes to it.
My stupid question is what is the best way to attach two 2"x2" timbers at the circled area (will I need ticker?) so that it doesn't fall apart in case some horizontal load is applied to the whole structure (I imagine not much force is needed at the top, so that the bottom breaks and wind might be a concern although I am planning to use it on a balcony)?