How to grow Asparagus

Where to plant

Choose a sunny spot for a permanent bed, with deep, well drained soil, at the side or end of the garden where the tall ferns will not shade other crops. Heavy, poorly prepared soil leads to crown rot and poor yields. Prepare the bed the fall before planting: work in compost or leaf mold, and lime only if a soil test calls for it.

Asparagus needs a cold or dry rest each year to build up the crowns. It grows well across the North, the Midwest, the Mountain West, the Mid-Atlantic, the Mid-South, the Pacific Northwest and Alaska, and in California and the desert, where the dry season gives the rest. In Florida, UF/IFAS warns that without a real dormant period the spears are smaller and more spindly than elsewhere; it can still be grown in North and Central Florida, but South Florida does not suit it.

Choosing a variety

Asparagus plants are either male or female. Female plants spend energy on seed and yield less, so all male hybrids now outyield the old Washington types by about three to one, according to Clemson. They are typically about 93 percent male.

How to plant

1. Buy healthy one year old crowns and plant them as soon as you get them, before they start to sprout.
2. Dig a trench 12 to 18 inches (30 to 45 cm) wide and 6 to 8 inches (15 to 20 cm) deep, with trenches 4 to 5 feet (1.2 to 1.5 m) apart. Mix compost into the soil you removed and spread a couple of inches back in the bottom.
3. Follow a soil test for phosphorus and potassium. Clemson advises putting the phosphorus into the bottom of the trench at planting, covered with at least 2 inches of soil, because it moves very slowly down to roots that will end up 6 to 8 inches deep.
4. Set the crowns 12 inches (30 cm) apart with the roots spread out, and cover them with 2 inches (5 cm) of soil.
5. As the shoots grow through the first summer, gradually fill in the trench a couple of inches at a time, without burying the ferns, until it is level.
6. Water well and keep weeds out; young asparagus competes poorly with weeds.

Watering and feeding

Good growth in the first year builds big crowns, so do not let young plants dry out. Water deeply to wet the soil at least 6 inches (15 cm) down, as light sprinkling gives shallow roots. Utah State suggests 1 to 2 inches of water every other week in the dry West for the first two years. Established beds have deep roots and need water mainly in long dry spells. Drip irrigation keeps the ferns dry and reduces disease.

Feed each year in early spring before the spears appear, guided by a soil test, and again lightly after the harvest ends to feed the fern growth. Top dress with compost every year and keep a 2 to 3 inch (5 to 8 cm) layer of mulch.

Pruning and care through the year

• Weed the bed in early spring before the spears come up, and pull weeds by hand during harvest so you do not snap the spears.
• Let the ferns grow all summer after harvest. They feed the crowns for next year's spears.
• Leave the ferns until they turn brown, then cut them to short stubs in late winter before new spears emerge. This also removes overwintering asparagus beetles and rust spores.
• Pull out female plants that bear red berries if you want to stop seedlings crowding the bed.
• In windy spots, support the ferns with stakes and string.

Harvesting

Harvest lightly for 3 to 4 weeks in the third year, as long as the ferns were tall and bushy the year before. Cut for about 6 weeks in the fourth year and up to 8 weeks once the bed is mature. In the North the harvest runs through May and June; in the South and California it starts in late winter or early spring.

Pick daily during the season. Cut or snap spears at the soil surface when they are about 6 to 9 inches (15 to 23 cm) tall, before the tips start to open, and do not cut deeper, which can damage the buds below. Stop when most new spears are thinner than a pencil. Refrigerate spears straight away, or freeze or can them.