Collection, Storage and Seedling-Raising Methods for Zanthoxylum Seeds of the Rutaceae Family

Zanthoxylum seeds are rich in oil, and their collection and storage requirements are fairly strict. Once the oil seeps out, the embryo becomes abortive and normal seedling raising is impossible. Therefore, for seeds intended for seedling raising, strict requirements must be applied starting from seed collection. So how are zanthoxylum seeds collected? How are they stored?

I. Seed Collection and Treatment

1. Seed collection

Select high-yielding, consistently productive mother trees with strong resistance for seed collection. Collect seeds when the fruit is fully mature, that is, when the outer pericarp shows the red or deep red color characteristic of the variety, the seeds are black and glossy, and 2-5% of the pericarps have split. Dry the collected fruits in the shade promptly, turning them 3-5 times a day. Once the pericarps have split, tap them lightly with a wooden stick and collect the seeds. The collected seeds should continue to be dried in the shade and must not be piled together, to avoid mildew.

2. Seed storage

(1) Sand storage  : Mix the seeds with moist sand in a 1:2 ratio and stir well. The sand should be moist enough to hold together in the hand without releasing water. Choose a high, dry site with good drainage, sheltered from wind and in the shade, and dig a storage pit 30 cm deep and 25 cm wide; the length of the pit depends on the amount of seed. First spread a 10 cm layer of moist sand on the bottom of the pit, then put in the sand-mixed seeds. When they are 10-20 cm from the ground surface, cover with another layer of moist sand level with the ground. After the seeds are placed, build a mound of soil above ground level. If there is a large amount of seed, a straw bundle can be placed upright in the center of the pit for ventilation.

(2) Dry storage  Float off the empty, shriveled seeds from the freshly collected seeds, then spread them in a cool, ventilated place to dry thoroughly in the shade, avoiding direct sunlight. Then put the dried seeds into open containers or bags; they must not be sealed, and should be kept in a ventilated, cool, dry room without direct light. They must not be stored in jars, crocks or plastic bags, as this impedes seed respiration and reduces seed viability. During storage, check regularly to avoid rodent damage, mildew and heating.

(3) There is a folk practice of mixing zanthoxylum seeds with fresh cow dung and sticking the mixture onto a wall, completing degreasing and overwintering in one step. Friends who are interested can give it a try.

3. Seed treatment

The seed coat of zanthoxylum is hard and covered with a relatively thick oily wax layer, so it does not readily absorb water and is difficult to germinate. Therefore, dry-stored seeds must undergo seed treatment before spring sowing.

The treatment method is as follows: for 100 kg of seeds, use 3-5 kg of washing soda (or quicklime, or laundry detergent), add an appropriate amount of warm water, soak for 3-4 hours, and rub vigorously and repeatedly to remove the oily skin completely, so that the seed coat loses its gloss and a pitted surface appears. Rinse the seeds with clean water 2-3 times, spread them in the shade to dry, and they are ready for sowing.

II. Seedling-Raising Techniques

Zanthoxylum is mainly propagated by sowing. The quality of zanthoxylum seedling raising depends on how the seeds are treated, because the seed coat is hard, contains a relatively large amount of oil and is impermeable to water, making germination fairly difficult; therefore, seed treatment is the key to raising zanthoxylum seedlings. Zanthoxylum can be sown in either spring or autumn. For autumn sowing, mid-to-late October is the best time, and the seeds need not be treated; spring sowing is generally carried out from mid-March to early April. Zanthoxylum is mostly sown in drills, with a row spacing of 15-20 cm and a furrow depth of 3 cm; a sowing rate of 10 kg per mu is appropriate. After covering with soil, press lightly, then cover with plant straw or plastic film, and remove the covering promptly once some seeds have germinated and emerged. After spring sowing, the seedlings generally emerge one after another within 10-20 days. When the seedlings have grown 2-3 true leaves, thin them promptly. After thinning, water and fertilize promptly, and carry out intertillage weeding and pest and disease control.

1. Sowing time

(1) Autumn sowing  Autumn sowing is carried out after seed collection and before the soil freezes. Sown at this time, the seeds need no treatment, and the seedlings emerge early the following spring and grow vigorously.

(2) Spring sowing  Spring sowing is generally carried out in early spring after the soil thaws. Seeds that have undergone sand storage are generally sown from mid-March to early April. The suitable sowing period is when the soil temperature at 10 cm below the surface reaches 8-10°C; at this time germination is fast and seedlings emerge evenly. However, the germination of sand-stored seeds must be checked at any time, and when more than 30% of the seeds show white at the tip, they should be sown promptly.

2. Sowing method

For the nursery site, it is best to choose sandy loam soil with irrigation available. Raising seedlings on such soil is convenient to manage, and the seedlings develop a well-developed root system and substantial above-ground growth. The nursery site needs crop rotation; land that has already been used to raise zanthoxylum seedlings should preferably be left for an interval of 2-3 years, otherwise the seedlings will grow poorly.

The nursery site should first be plowed to a depth of 30-40 cm, and 5000-6000 kg of soil manure or barnyard manure per mu should be applied along with the plowing. Then level it and make beds, generally 1-1.2 m wide, with 3-4 rows per bed. In the north, spring is generally fairly dry, so the site should be fully irrigated before sowing. When sowing, first open furrows in the bed 5 cm deep, spread the seeds evenly in the furrows, then cover with soil, rake level and press lightly. After sowing, cover the bed surface with a layer of straw to help preserve moisture and prevent bird damage. In relatively dry conditions, to help preserve moisture, the covering soil in the sowing furrows can also be thickened by 2-3 cm to form a ridge shape, then leveled off again when the seedlings are about to emerge, to facilitate their emergence.

The sowing rate should be determined according to seed quality. Zanthoxylum seeds generally contain a relatively large proportion of empty, shriveled grains, so the sowing rate should be appropriately larger; for rinsed seeds, the sowing rate is 40-60 kg per mu.

3. Seedling-stage management

(1) Thinning and transplanting: When the seedlings have grown to 5-10 cm, thin and space them. The spacing should be maintained at about 10 cm, with about 20,000 seedlings per mu. The thinned seedlings can be moved with their soil to fill gaps, or moved to other seedbeds for growing on.

(2) Intertillage and weeding: When the seedlings have grown to 10-15 cm, pull up weeds in good time so they do not compete with the seedlings for fertilizer, water and light. Afterwards, carry out intertillage and weeding as needed according to weed growth and soil compaction in the nursery, generally 3-4 times during the seedling growing period, so that the nursery soil remains loose and free of weeds.

(3) Fertilization: After the zanthoxylum seedlings emerge, they begin rapid growth in mid-to-late May, and enter their period of most vigorous growth in mid-to-late June, which is also the period of greatest demand for fertilizer and water. During this time, apply topdressing 1-2 times, with 20-25 kg of ammonium sulfate per mu or about 1000 kg of decomposed human manure and urine. For those growing weakly, apply another quick-acting nitrogen fertilizer in early-to-mid July. Nitrogen topdressing must not be applied too late, otherwise the seedlings cannot shed their leaves on time and have poor lignification, which is unfavorable for overwintering.

(4) Irrigation: Do not irrigate before the seedlings emerge, otherwise the soil tends to become compacted and the seedlings have difficulty emerging. After emergence, decide whether to irrigate according to weather conditions and soil moisture content. Generally, it is best to irrigate once immediately after fertilizing so that the fertilizer takes effect as quickly as possible. In places with excessive rain, pay attention to timely drainage to prevent waterlogging and avoid standing water.