Asparagus is a long-lived perennial vegetable, offering a harvest that can last for two decades or more once established. Starting an asparagus patch from seed is a patient endeavor, requiring several years before a significant harvest can be enjoyed. It is a highly economical method compared to purchasing crowns, giving the gardener full control over the plant’s initial growth. Success depends on precise, step-by-step care in the initial stages.
Preparing Asparagus Seeds and Timing
Scarification is highly recommended to improve the germination rate of asparagus seeds, which naturally have a tough outer coat. This is accomplished by soaking the seeds in warm water for 12 to 24 hours. Soaking helps to soften the seed coat and allows moisture to penetrate more readily, which significantly reduces the time it takes for the seeds to sprout.
Asparagus seeds should be started indoors 10 to 12 weeks before the last expected spring frost. Use a sterile, well-draining seed-starting mix in containers that offer sufficient depth, as asparagus seedlings quickly develop long taproots. Individual cells or pots that are at least two inches wide are preferred to prevent the young plants from becoming root-bound prematurely.
Planting Depth and Initial Spacing
Sow asparagus seeds between one-half (1/2) inch and three-quarters (3/4) inch deep. This shallow depth provides enough protection for the seed while still allowing the emerging shoot to reach the surface without expending too much energy. Once the seed is placed in the container, cover it gently with the seed-starting mix and lightly firm the soil over the top.
Proper spacing is important to manage competition among the emerging seedlings. If using individual pots or cells, place one seed per container to eliminate the need for thinning and reduce root disturbance. If sowing in a tray, maintain a minimum spacing of two inches between seeds to allow room for the developing root systems until transplanting.
Care During Germination
Asparagus seeds require specific warmth to break dormancy and begin to grow. The soil temperature must be maintained consistently between 70°F and 85°F for the best and fastest germination. Using a seedling heat mat beneath the containers is often necessary to provide this steady warmth. Once the seedlings emerge, the soil temperature can be slightly reduced to between 60°F and 70°F.
Maintaining moisture is also a delicate balance during this phase, as the seed-starting mix needs to be consistently damp but never waterlogged. Overwatering can lead to fungal issues like damping off. The initial emergence can take time, sometimes as long as three to eight weeks. After the seedlings have pushed through the soil, they need a strong light source, such as a dedicated grow light, to prevent them from stretching and becoming weak, or “leggy”.
Transplanting Seedlings to the Permanent Bed
Seedlings are typically ready to transition to the permanent outdoor location when they are 12 to 16 weeks old and have reached a height of six to ten inches. Before planting them into the garden, the young plants must be hardened off by gradually exposing them to outdoor conditions over a period of one to two weeks. This process involves slowly increasing their time outside, shielding them from strong sun and wind initially, to acclimate them to the harsher environment.
The permanent bed requires deep preparation, with the soil loosened to a depth of 10 to 12 inches and amended with organic matter to ensure fertility and drainage. A common method is to dig a trench, or furrow, that is about eight to twelve inches deep and wide. The seedlings are placed into this trench, with their roots spread out, and initially covered with only two to three inches of soil.
As the young plants grow throughout their first season, soil is gradually pulled into the trench to cover the crown more deeply. This continues until the trench is entirely filled and level with the surrounding garden space. Final spacing between plants should be 12 to 18 inches, with rows separated by three to six feet to allow for the mature size of the perennial crop.