Rhubarb is a great plant and easy to grow.
March is the time to mulch established plants and to sow seed, if you are growing new plants. You can read about growing and caring for rhubarb, here
Start planting early potatoes.
Whether you have chitted or not (see more), you can get early potatoes into the ground in late March.
March is the time to plant wildflower mixes
Creating a wildflower meadow is a wonderful way to attract wildlife into your garden and now is a great time to prepare the ground and sow the seed.