Asparagus (Asparagus officinalis)
Asparagus is a member of the lily family (Liliaceae) and is one of a few vegetables that are monocots (plants having only one cotyledon, or seed leaf). Asparagus plants are dioecious, meaning female and male flowers are produced on different plants.
Planting
Asparagus can be started in a greenhouse for about 8 to 10 weeks before being transplanted outdoors. When directly seeding for later transplant, it's recommended to space plants 2 inches apart within the row and keep 24 inches between rows. For direct seeding without thinning and transplanting, aim for a plant density of around 12,000 to 14,000 plants per acre. In this case, space the plants 12 to 18 inches apart, with rows spaced 3 to 6 feet apart.
When transplanting, place the asparagus in an 8-inch-deep furrow, shaping the bottom of the furrow in a W pattern beneath the soil. Over the course of the growing season, gradually fill in the furrow with soil. It’s best to plant asparagus in May, allowing the foliage to develop fully before winter.
Soil
Asparagus can thrive in a variety of soil types and conditions, but it performs best in well-drained, non-compacted soils that retain moisture, with an optimal pH range of 6.2 to 7.0. It's important to avoid planting asparagus in fields where it was previously grown. The plant is also resilient to significant temperature fluctuations.
Irrigation
Irrigation is strongly advised to help maintain a consistent crop each year. Trickle irrigation is ideal compared to overhead systems, as it delivers water directly to the root zone without wetting the foliage. This method also minimizes water loss due to evaporation.
Harvest
The asparagus harvest period gradually extends over the years, starting with about 7 days in the first year and growing to a 6 to 7 week harvest window by full maturity at around 5 years. Spears should be harvested when they reach at least 7 inches in height, with a minimum diameter of 5/16 inch, and when they are green. Since spears can grow as much as 2 inches a day, daily harvesting is recommended.
Purple-speared varieties are also available commercially. By excluding light during spear emergence, white or blanched asparagus can be produced. Spears can be harvested by cutting with an asparagus knife or snapping them off near the soil surface.
Storage
To extend shelf life and preserve quality, asparagus should be cooled right after harvest to remove field heat. Immediate refrigeration is crucial for maintaining its freshness. When stored at temperatures between 32 and 36°F with a relative humidity of 90 to 95 percent, asparagus can maintain its quality for about 7 to 14 days.
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