They are very easy to grow and are much less work than the annual broccoli which has to be sown and grown again and again each year. Growing perennial broccoli. These plants can be grown from seed in the spring in much the same way as annual broccoli plants.Once the plants are large enough they can be planted outside into a permanent position. They grow to about 50cm - 100cm high and can have a spread up to 100cm so leave enough room for them to grow.he leaves taste like cabbage and can be picked all year round which makes this really useful plant for winter greens. The broccoli heads and the leaves can be picked as a cut-and-come-again crop. Benefits of perennial plants. Perennials save the gardener time and money with a one time only purchase and planting.