How and When to Harvest Asparagus

Among the tastiest and highly prized of all garden vegetables is asparagus (Asparagus officinalis). Part of the allure of asparagus is that this perennial vegetable is the first vegetable harvested in the spring. Fresh asparagus is in premium demand, and a gardener with a thriving patch of asparagus can save a notable amount of money at the grocery store. The ferny growth is also an attractive addition to the garden. 

Patience Pays Off

Unlike other vegetables, growing asparagus needs considerable patience because it takes three years before you can harvest the spears. This requires some discipline on your part—the spears will appear in the first and second year, but if you harvest them then, you will very likely kill the plants, or seriously stunt their production for future years.

But if you have planted the crown correctly, fertilized appropriately, and cared for your asparagus for two years, in the spring of your third year, your plants will produce a crop that will provide you fresh asparagus each year from early spring until July 1 for about 15 years or so. You can harvest up to 24 times per season by the time the plant is mature. The second year you'll harvest less often, but by the third you can harvest every six to eight weeks.

How to Harvest

Harvest asparagus by cutting the spears at ground level when they emerge in spring before any flower buds at the tips begin to open. Spears are ready to be harvested when they've reached 6 to 10 inches tall and about the diameter of your index finger. Use a clean, sharp knife or gardening shears. Continue harvesting asparagus spears for six to eight weeks, but no later than July 1.

If you notice decreased production and vigor in your asparagus plants, stop harvesting and let the plant store energy for next season. Any spears that reach a height of more than 10 inches should be allowed to continue growing to strengthen roots and store energy for next year.

Planting Tips

Asparagus plants are heavy feeders, so be prepared to amend your soil and fertilize regularly. Because the edible part of the plant is the stem (spears) rather than the leaves, phosphorus, not nitrogen, is the primary nutrient required by the plants.

1. Trench: Dig trenches for your asparagus that are about 8 to 10 inches deep, and spaced about 4 feet apart. 
2. Fertilizer: Spread a fertilizer high in phosphorus in the bottom of the trench and mix it in. A 0-20-0 fertilizer is ideal (the numbers represent the percentage of nitrogen N, phosphorus P, and potassium K, respectively, in the fertilizer). An organic fertilizer option is a layer of bone meal mixed into the bottom of the trench.
3. Plant the crowns: Place the purchased asparagus crowns flat in the trench. Space them 12 inches to 18 inches apart. Cover with about 2 inches of soil, and water the area lightly. 
4. Add more soil to the trench: When 2 inches of new growth appears, backfill the trench with more soil. Do this several times as new growth appears until the trench is filled in. 
5. Maintenance: Keep the area weed free, and fertilize annually in the spring with a balanced fertilizer. You can also keep the soil rich and help feed the asparagus plants by top dressing the soil annually with compost. Do this in early spring before the spears appear or in the fall after the fronds have died back and been cut to the ground.
6. First harvest: In the third year, make your first light harvest. Once the plants become more robust in subsequent years, you can harvest more heavily. If you notice a decline in robustness after several years, you might want to divide and transplant your asparagus.