It depends on your climate and weather conditions. If it's temperate and sunny enough, you can probably grow some kind of greens for most of the year. I've grown a variety of salad greens during summer. The key is to keep rotating batches in, so you always have fresh greens ready. Most crop varieties don't stay ripe and fresh too long, so ongoing planting is needed.If I eat 7 salads a week, is it possible to grow enough spinach on a 10 x 3 balcony to sustain you in times of food shortages where you can't buy these items at the store?