Perennials are plants that grow back every year. Although they may lose their leaves and die down to the soil during the winter months, these plants display new growth as the soil warms up in the spring and summer. Perennials have hardiness ratings that help gardeners determine how well certain varieties thrive in specific climate zones. Many plants that grow as perennials in warm, semitropical climates, grow as annuals in cooler areas, due to their inability to withstand freezing temperatures.
Several types of root vegetables grow throughout the year and multiply from sections remaining in the ground during harvesting. The soil helps insulate root vegetables during cold temperatures. Many root vegetables make additions to the table throughout the year whenever the soil is soft enough for digging. Perennial root vegetables include several varieties of onions, potatoes and garlic. Welsh onions are one perennial vegetable than many gardeners grow as annuals. Commonly called scallions, these vegetables grow from seeds or through clump division. The harvested bulbs and greens both make flavorful additions in recipes and salads. Piling fresh straw over root vegetables grown in U.S. Department of Agriculture Plant Hardiness Zones 6 and cooler helps insulate the plants from extreme temperatures.
The brassica family of plants includes several perennials, such as broccoli and collards. Other perennials producing edible shoots, leaves and fruits include nettles, collards, sorrel and artichokes. Asparagus is one of the most common perennial vegetables in gardens. Asparagus grows from crowns and may take 2 or more years to produce a crop large enough for harvesting. Depending on the variety, asparagus can grow in climate zones as cold as USDA zones 3 and 4. The young spears appear early in the spring. Cutting these off near the ground allows the roots to continue to grow each year.
Perennial herbs grow in a variety of settings, often among flowering plants or alongside vegetables in the garden. Herbs that come back every year include catnip, chives, lemon balm, garden sage and winter savory. Thyme and oregano are two herbs that grow in climate USDA zones 4 and warmer. Both herbs grow about 24 inches tall and make flavorful additions to meat dishes.