Your rhubarb should be harvested in the spring after the large leaves unfurl. Just pull away the outermost leaves, leaving one-third of the leaves for the plant to use for summer energy. It is good that you did not harvest your rhubarb this year, as it takes a few years for the plants to mature to harvest size. You will only be eating the stem of rhubarb as the leaves themselves are toxic. Horseradish is harvested in the fall by digging up the thick roots and letting them dry before chopping or grating the roots for seasoning. You can also plant lettuce, garlic and Swiss chard in late summer for harvest in the spring. Welcome to vegetable gardening, and Keep Growing, Marianne Binetti