What Conditions Are Needed for Growing Asparagus? Detailed Guide to Seed Treatment

Asparagus, also known as shidiao cai (Asparagus officinalis), is hailed as “the king of vegetables”. Asparagus that has not emerged from the soil is white and is called white asparagus; after emerging it turns green and is called green asparagus. Its tender shoots are delicious and tasty when cooked, and are a favorite of many people. So what conditions are needed for growing asparagus? What are the seed treatment methods?

1. What conditions are needed for growing asparagus?

1. Temperature

Asparagus is highly adaptable to temperature. The starting temperature for growth and development is 5°C, the maximum suitable temperature is 37°C, and the optimum temperature is 12-26°C. During dormancy, the underground parts can tolerate low temperatures of -38°C. Therefore, asparagus can be cultivated from subtropical to subfrigid zones, but temperate regions are most suitable.

The starting temperature for asparagus seed germination is 5°C, the optimum temperature is 20-25°C, and the germination rate can reach over 90%; above 30°C, the germination rate and germination vigor decline noticeably. Soaked seeds can germinate in 3 days at 25°C. Asparagus tender stems begin to grow above 10°C, with growth being best at an air temperature of 15-17°C and the quality tender; plant growth is fastest at an air temperature of 20-30°C, and stops at 5-6°C; when the air temperature is above 30°C, the surface of the tender stems easily becomes fibrous, and plant growth is also slow.

2. Light

Asparagus is a light-loving crop and has relatively high light requirements. If light is insufficient during the period of vigorous growth of aboveground stems and leaves, it will seriously affect the production and accumulation of assimilates, as well as the growth and development of asparagus, thereby reducing the yield and quality of the tender stems in that year. According to Sawada's experiment (1961), on sunny days (sunshine duration of more than 10 hours), the carbon dioxide assimilation per 5 grams of cladodes was more than 130 mg, while on cloudy or rainy days (sunshine duration of less than 7 hours), the carbon dioxide assimilation per 5 grams of cladodes was only about 110 mg. This shows that sufficient light on sunny days is beneficial to photosynthesis in asparagus. Therefore, when planting asparagus, sunny plots should be selected, and reasonable close planting should be adopted to avoid excessive density that causes the field to become closed and shade each other. Planting in a north-south direction helps improve photosynthetic efficiency.

3. Soil

To promote the development of the asparagus root system, the soil chosen for cultivating asparagus should preferably be deep and loose in the soil layer. Humus soil or sandy loam with suitable aeration, rich in organic matter, and strong water- and fertilizer-retention capacity is suitable. Shallow soil layers, poor aeration, easily compacted, poorly drained clay and gravelly soil, as well as plots with a high groundwater table and poor drainage, are all unsuitable for growing asparagus.

Asparagus requires soil pH of 5.8-7.5 as suitable. Strongly acidic or alkaline soil should be avoided; in soil with a pH above 8 or below 5.5, the root system develops poorly, growth stops or the roots rot, the aboveground stems dry up, and quality declines severely. Experiments have shown that on plots with a pH of 7.8, growth and development are still good, with little effect on the yield and quality of the tender stems. When the soil pH is below 5 or above 8, plant growth is indeed inhibited and yield decreases.

Asparagus has a relatively strong salt tolerance, and generally a soil salt content of no more than 0.2% is most suitable. According to experience in saline-alkali areas, asparagus grows well on plots with a soil salt content of about 0.25%, but when it is above 0.3%, plant growth is affected, stems and branches become thinner, and the plants may even gradually die.

4. Water

Asparagus is not tolerant of waterlogging. If the soil has excessive water for a long time, or the groundwater table is too high, drainage is poor, or the plot is often waterlogged, it is easy to cause insufficient oxygen in the soil, which obstructs root respiration, causing poor growth or root rot in asparagus, or even death of the entire plant. In addition, if air humidity is too high and is combined with high temperatures, it can also easily lead to asparagus diseases, especially a massive outbreak of stem blight. Therefore, land with superior irrigation and drainage conditions should be selected. When cultivating asparagus on dry slopes without irrigation conditions, the horizontal deep-furrow cultivation method should be used, and work on retaining floodwater and preserving soil moisture during the rainy season should be done well.

However, during the harvest period of asparagus tender stems, sufficient water is needed; otherwise, the tender stems will be few and thin, the growing buds will shrink back, they will easily become old, and quality will decline.

5. Nutrients

The various nutrients that asparagus needs during growth and development mainly come from two aspects: one is the nutrient supply from the soil itself, and the other is the supplementation of various nutrient elements through soil fertilization. This is the key to ensuring normal growth and development of asparagus and achieving high quality and high yield. The effects and roles of various nutrient elements on asparagus differ noticeably.

2. Seed treatment methods for growing asparagus

At present, asparagus seeds are expensive and costly, and direct sowing makes land use very uneconomical, so cultivation generally adopts the technique of raising seedlings in a nursery and then transplanting.

1. Seedling raising time

Open-field seedling raising can be sown from early April to early August, while seedling raising in small arched sheds can be carried out earlier in early March.

2. Seedbed site selection

For the seedling site, sandy soil with fertile soil, good aeration, and relatively good drainage and irrigation conditions should be selected, and plots with few weeds, especially few perennial weeds, should be chosen.

3. Seed treatment

Asparagus seeds have a thick coat with a relatively thick waxy layer, making it difficult for them to absorb water. Before sowing, seed soaking and sprouting, as well as chemical treatment, are necessary before sowing.

Soak the seeds for 12 hours in a 300-fold dilution of 50% carbendazim (or 75% chlorothalonil wettable powder); then after rinsing with clean water, soak the seeds in warm water at 25°C-30°C for 24 hours, changing the water 1-2 times a day. When changing the water, repeatedly rub and wash the seeds to remove the mucus, shriveled seeds, and impurities on the seeds.

4. Sowing

Wrap the soaked seeds in a damp cloth and place them at 25°C-28°C for sprouting. Rinse with clean water 1-2 times a day, and sow once 5%-10% of the seeds have sprouted.

Before sowing, the nursery land should be given sufficient base fertilizer, and level beds 1.1 m wide should be made. Single-seed sowing should be adopted. The sowing depth depends on the temperature conditions, and the sowing density is 10 cm × 10 cm.

Overall, asparagus is used both as food and medicine and can be used to make beverages, tea, health products, canned goods, etc. It has large market demand and high profits, and one planting can grow for 15 years. In asparagus cultivation, it is very necessary to clearly understand the conditions for growing asparagus and the seed treatment methods. The above content is hoped to provide everyone with a reference.