A few months back we took a look at the plans to build a portable salad table. Although we loved that idea dearly, this model is even better because it's self-watering! The materials list is simple and construction is easy enough for anyone to take on.
If your job keeps you away from home (or you just don't want to water things twice a day), check out this simple idea from Instructables user KindleKat for a self-watering table that's perfect for salad fixings, herbs and more. It's really just a simple frame with plastic tubs. A smaller tub is turned upside down and placed inside with a piece of PVC tubing sticking out the top, dirt is added, then water and more dirt, and finally plants.
Even if you don't have time to tackle a project like this now, it's a good one to file away for later. If your space is smaller, try decreasing the size so it only holds one or two buckets making it a bit more patio friendly.