Planning for Perennial Crops – Vegetables

Rhubarb and asparagus are the best-known perennial vegetables, but they are by no means the only ones. Other less-commonly grown perennial vegetables include artichokes, sorrel, nettles, Jerusalem artichokes, and dandelions. These plants should be grown in dedicated beds, or in containers if the plants are invasive in nature, like dandelions. With the exception of nettles, which can be foraged from the wild, keep the perennial beds well-weeded, top dress with organic compost every spring and cover the beds with 6 to 12 inches of leaf mulch after harvesting every year.

Rhubarb – Rheum rhabarbarum

Rhubarb thrives in cool locations and full sun in deep, moist, well-drained soil. Prepare holes at least 18 inches deep and 3 feet wide and enrich with 6 inches of compost. Space 3 to 4 feet apart in rows 6 feet apart. Set the crowns 1 or 2 inches below the surface of the soil.

Don’t harvest the first year, to allow the plants’ energy to go into growing a strong root system. In the second and third years, only harvest a few stems. By their fourth season, the plants will be mature and you can harvest up to half of the stems per season. Stop harvesting when the stalks start getting thin. These plants remain viable for 10 to 15 years. When production starts to fall off, propagate by root division.

Remove flower stalks to keep rhubarb plants productive. DO NOT eat the leaves or roots; they contain oxalic acid, which is poisonous. Hard frosts can force the oxalic acid into the stems. Remove any affected stems and discard them.

Asparagus – Asparagus officinalis

Asparagus needs full sun and excellent drainage with protection from strong winds. Asparagus thrives in light, sandy loam with a neutral pH. To prepare the bed, grow a cover crop the previous season, or add a couple of inches of organic compost and turn it under to a depth of at least 10 inches to accommodate the extensive root system.

Allow 18 to 24 inches between plants in rows spaced 3 to 4 feet apart. Dig trenches 6 to 10 inches deep and a foot wide. Build a 2 inch mound of soil or compost down the center over which to drape the roots of the asparagus crowns. Cover with 2 inches of soil and add another 2 inches of soil every two weeks until the trench is filled and slightly mounded. Sprinkle alfalfa meal over the bed and then mulch 6 to 12 inches deep with organic mulch.

Select all-male cultivars for higher yields. One-year-old crowns are less prone to transplant trauma than 2-year-old crowns. Wait until the third year to harvest to let the crop develop a strong root system. Gradually lengthen the cutting weeks every season until you are harvesting up to 8 weeks per season.

Other Perennial Vegetables

• Artichokes (Cynara scolymus)/cardoon (Cynara cardunculus) – these are grown in similar conditions, and as annuals in Zones 4 – 7. These big plants need lots of space and cool, moist conditions to thrive. Flower buds are harvested from artichokes; cardoon utilizes the heavy ribs of the leaves.
• Dandelion(Taraxacum officinale) – harvest young leaves of established plants until they turn bitter in warm weather; use raw in salads or steamed like spinach. A very good source of dietary fiber, Vitamins A/B6/C/E/K, thiamin, riboflavin, calcium, iron, potassium and manganese. Do not let the flowers go to seed.
• Jerusalem artichokes (Helianthus tuberosus) – a species of sunflowers and a reliable source of mild-flavored tubers. Grow in full sun and loose, rich soil. Plant tubers 2 to 6 inches deep, 12 to 18 inches apart. Space rows 36 inches apart. Can be very invasive once established.
• Nettle (Bioforce urtica) – wear gloves and pants tucked into socks when harvesting this stinging plant that grows wild in moist ground. When boiled for a few minutes, the sting is removed. Nettles are dense in nutrition with very few calories, high in potassium, iron, sulphur, vitamin C, vitamin A and B complex vitamins.
• Sea kale(Crambe maritima) – valued for its early shoots, which are blanched under an inverted basket in early spring until harvested like asparagus when the shoots are 6 to 8 inches long. In the third year, harvest young plants for 1 or 2 weeks; older plants for 3 to 4 weeks. After harvesting, remove the baskets and let the plants grow normally.
• Sorrel (Rumex acetosa) – a common garden weed with a lemony taste, sorrel prefers acidic soil and tolerates partial shade. Cut the young leaves as needed all summer and remove flower stems as they appear. Propagate by section cuttings.

For other articles in this series on Planning Perennial Crops, please read Fruit & Nut Trees, Brambles, and Fruiting Bushes.