Vegetables are propagated either by vegetative methods or by means of seed, depending on the crop. Examples of those usually propagated vegetatively are potato (“seed” tubers), sweet potato (generally vine cuttings), garlic (bulbs are divided in cloves, with larger ones being used as seed for planting). However, most vegetables are produced from true seed, and it is this aspect which will be dealt with.
Most plants can be successfully transplanted at a very young age. However, this period is short for certain crops, such as various beans, carrot, cucurbits, peas, sweet corn and so on, that the disadvantages of transplants usually far outweigh the advantages, and transplanting is seldom a practical consideration. Such crops are thus sown directly into production field in their paramount positions. Even those crops which may be successfully transplanted are, at times, seeded directly into the production field.
It is true to use quality seed that is true to type, has a high germination percentage, has a high vigour, has no dormancy, is free of foreign matter and has no disease contamination. Two types of seed are available: open pollinated and HYBRID seed. Hybrid seed is more expensive, but improved crop uniformity can be expected due to the selection of favourable characteristics. Hybrid seed is a combination of two or more genetically distinct parental inbred lines. Open pollinated (OP) seed is cheaper but yield is not as good as hybrids. It is important to take note of the batch number or reference number of all seed used (attached to your invoice and date of purchase) so that any problems which may arise can be discussed with the relevant seed supplier.
The land preparation for direct seeding should be at least as good if not better than that used for Transplants. The field should have a good tilth without any large clods, should be firm and as level as possible. An uneven surface leads to an uneven depth of planting, resulting in less uniform emergence, growth and maturity. Obviously any basal fertilizer dressings should be worked in before sowing. Sowing will generally be deeper on sandy soils than heavy soils. Planting depth for larger seeds, such as beans, peas or sweet corn, may be also a bit shallow, but it is usually for bigger seeds, for them to be drilled / planted two and a half times the diameter of the seed. Firm down the soil over the seed after planting to ensure good seed to soil contact. It is usually better to plant into moist soil, which has been wetted to the rooting depth of the crop a few days previously, and then to give a light irrigation soon after planting to settle the soil around the seed. Make sure that the soil around the seed remains moist by frequent light irrigations until plants emerge- remember the top layer of soil dries out rapidly. For hand planting of seed on can soak the seed over night before planting. Seed needs to absorb 30% of its weight of water before it germinates. Note all seed soaked overnight has to be planted as it can’t be kept after soaking.
Apart from the crops discussed above, there is another group which transplant comparatively easily and successfully, even at a more advanced age. These include crops such as brinjal, broccoli, Brussels sprouts, cabbage, cauliflower, chill, lettuce, sweet peppers and tomatoes. It is common practice to raise them in seedbeds or seedling trays, for later establishment in their permanent positions in the field.
The main advantage of transplanting seedlings revolves around the fact that the area used for growing transplants is small in comparison with the size of the production fields. This results in:
• Better utilization of available ground, because the larger fields may be used for crop production while seedlings are being produced.
• Seedlings take between 4 to 6 weeks before transplant depending on the variety. Talk to the nursery when the seedlings will be ready for collection.
• Better germination, seedling growth, and plant survival, resulting in lower usage of seed, because small seedbeds / seedling trays can better looked after.
• Better, quicker and cheaper control of pests, diseases and weeds.
• Better control of irrigation, with saving in water usage, and more frequent watering, ensuring consistent seedling growth.
• Easier and better protection of seedlings against wind, hail, rain, heat and cold.
• Earlier cropping is possible in areas with cold winters by producing seedlings under cover, or in a warmer are, and transplanting when outside conditions become favourable for growth.
• More uniform plant spacing, as well as replacement of “missing or eaten” plants when established in the field.
The disadvantages of seedlings include:
• The unavailability of seedlings due to bad planning by the grower, ordering in time for his plantings.
• High cost of seedling vs. producing them yourself
• Labour needed for transplanting vs. direct planting of certain veggies.
• Transplanting losses may, under unfavorable conditions, result in a poor stand and low yields.
• The time taken from sowing to harvest is normally extended because plant growth may be set back to some extent by transplanting of some varieties of vegetables.
Transplants are usually raised in seed trays or in open seedbeds. Seed trays are normally used by nurserymen producing plants for sale to growers. The majority of vegetable producers buy seedlings from nurseries. Although a few vegetable growers do grow their own seedlings because of quality control and specific varieties that they want to grow.
The quality, including age, of transplants plays a large role in determining the potential yield of the resultant crop. Seedling production should, therefore receive special attention from each grower, because poorly grown seedlings can never produce the yields, nor quality, that can be achieved with young, strong, healthy transplants.
In commercial practice there are two main methods of producing transplants / seedlings. The first is to produce the seedlings in seedling trays, using coir / vermiculite / composted pine bark as a growing medium, and under cover, and the other is to grow the seedlings in soil in seedbeds situated in the open.
In Swaziland most transplants are produced in seedling trays and mostly by commercial nursery men. Most commonly used structures in which the seedlings are produced are shade houses, which use shade cloth. Use is made of black 20% shade cloth for vegetable seedlings.
Should the seedlings be grown in trays placed directly on the ground, or any other solid surface, their roots will tend to grow out the drainage holes at the bottom of the cavities (or Cells). At transplanting this would cause difficulty in removing seedlings, would damage the roots, causing a greater transplant shock and plant setback, and would negate most advantages of raising plants in such containers. If the trays were to be raised about 60 cm above ground, with drainage holes exposed to the air, roots do not grow out of them and would remain within the cell cavity, with much better transplanting results. To achieve this, two parallel lengths of 16 gauge wire(60 cm apart) are drawn taut over a pole structure about 60 cm high and spaced 2,8 m apart down the rows. The ends of the seedling trays rest the wires, thus allowing a free flow of air past the bottoms of the trays.
The trays used for large scale production are usually 670mm long, 340mm wide and 50 to 60mm deep. The numbers of cavities per tray vary. The fewer the cavities per tray, the larger the cells are, and the longer the seedlings can be kept before becoming root bound. The cost of producing each seedling is appreciably higher, as fewer seedlings are produced over time per unit area, and more growing medium is used per plant in large cavities. Because of this cost factor, nurseries favor the use of trays with many small cavities, hence the use of 200 cells, or even 128 cells for certain crops such as tomatoes and peppers.
Well decomposed pine bark, coir and vermiculite is weed free and recommended for seedling trays. Seed is normally planted mechanically into the tray cavities. Very important that seed is placed at the correct depth and in the center of the cavity for good root growth. The trays are then lightly watered and placed in a germination room with high humidity and a moderate temperature of between 20 to 25 ˚C. About 3 to 5 days later the trays are removed and placed on the racks where they are watered, often several times during the day depending on the temperature and the time of the year. Nutrients are added to the watering to stimulate growth after germination. Drainage within the nursery area is very important to combat disease. To prevent disease the trays are sterilized after use before next planting, either by means of steam or chemical means such as Copper Oxychloride or Spore kill. It is essential with seedling production to maintain good sanitation in the nursery.
The copper in products helps with root pruning and prevents root caging. Root caging occurs when the roots reach the cavity wall and grow down, which will reduce the plants rooting volume. The copper on the other hand cauterizes the roots causing a pruning effect when it reaches the cavity wall; subsequent lateral growth of the roots results increased root volume of the plant. Most trays also taper and are open at the base of each cavity, which causes air pruning.
OPEN SEED BED
The site for a seed bed must be carefully selected. It should be easily accessible, because the seed beds should be inspected and attended to daily, in order to make management decisions on irrigation, pest and disease control. Avoid using soils subject to capping (crusting); preferably, select lighter soil types, such as sandy loam soils. These soils warm up quickly, generally drain well, are easier to cultivate, and most seedlings will emerge more easily, and grow better. Frequent light watering’s required for optimum germination and growth. Bed can be covered with thatching grass to help with moisture control especially seed planted very shallow e.g. Cabbage and other fine seeds. When germination takes place the straw can be raised by putting plastic pipes between rows to raise the straw and therefore acclimatize the seedling to the sun. The site should be protected from cold and wind. Good air circulation is advisable around seedlings in order to reduce disease incidence. Soil seedling beds can be sterilized with boiling water before planting of seeds. Avoid low lying areas where cold air drains. Beds must be rotated and treated for nematodes.
The Soil needs to be well prepared, and in good tilth. As most transplanted vegetables have relatively small seed, the soil surface should be fine, but not pulverized. In many instances, soil fumigation may be advisable for the control of nematodes: certain weeds, and other pests and diseases, may also be controlled with some of these chemicals. A soil test for where your seedling beds should have been done long before the planting date. The soils should be limed if necessary, and should be well fertilized. On soils of low fertility, a pre plant incorporation of about 10 kg per 100 m² of a general fertilizer mixture such as 2:3:4 (39) + Zn should be adequate for most seedling crops. Beds are usually made about 1, 0 m wide, and of any convenient length. They should be level across their width, with no high spots (too dry) or low spots (too wet). The beds are usually raised about 150 mm above the access pathways between them, to facilitate GOOD drainage.
The seed is sown thinly, usually in shallow furrows drawn 100 mm to 150 mm apart, and covered to a depth of 3 to 10 mm depending on the size of the seed. Seed should always be sowed to a depth of two and a half times the diameter of the seed. In order to prevent overcrowding of seedlings, rather err by sowing too thinly than too densely. As a general rule, sow about 100 to 150 seeds per running meter of plant row.
The seedling rate for any crop will obviously vary, depending on the number of seeds per gram of the particular seed lot, its germination ability, the growing conditions to which it is subjected, and the plant population desired on the land. Contact Diccon Robinson Cell: +268 7602 5482 for seeding rate per hectare. Common seedling rates for a hectare are 300 to 400 g for most Cole crops (cabbage family). 250 to 350 g for capsicums (chilies and sweet peppers), 250 g for tomatoes, 500 g for brinjal (egg Plant) and lettuce, and 3 to 5 kg for onions. Many growers customarily sow 10 to 15% more seed than considered necessary, to ensure that there are sufficient plants, even after fairly stringent selection of the seedling to be planted out.
After sowing, frequently, (daily or even twice daily during hot, dry weather, light irrigations are necessary to prevent the drying out of the top soil in which the seed is planted, after emergence, gradually increase the interval between irrigations as the plants become stronger. Ensure than seedling beds do not become too wet, because such conditions favours the development of many diseases, especially damping off and foliar diseases.
If seedlings have been produced under shade cloth or other shelter, the cover should be gradually removed or moved outside to acclimatize the plants to the outside conditions. Hardening, which is the process of adapting seedlings to field conditions, should take place 7 to 14 days prior to transplanting. Harding will increase the transplanting success rate, to do this withhold moisture or reduce / increase the temperature to which the seedlings are exposed to.
Give beds a good soaking a day before transplanting to facilitate lifting of the seedlings with minimal root damage. Just remember what is above the ground is below the ground in root development. Don’t prune the roots when lifting seedlings in the beds. Wrap seedlings in paper to transport in crates to the fields to plant out. Under warm conditions, most seedlings will reach the transplanting stage 4 to 6 weeks, but this period may double under colder conditions. Traditional transplant size is when the plant is at the 5 to 6 true leaf stage. During growth in the seedbeds, attention to weed control, as well as the control of pests or disease, should receive priority.
Transplanting should be done as late in the afternoon as possible in Summer or as early as possible in the mornings in Winter. Water seedlings directly after transplanting. Special attention should be paid to further irrigation, and replacing any dead or weak plants, until the seedlings have recovered from any transplanting shock.