The first step in successful vegetable production is to raise healthy vigorous seedlings. Young
plants whether propagated from seed or vegetatively require a lot of care particularly during the
early stages of growth. They have to be protected from adverse temperatures, heavy rains, drought,wind and a variety of pests and diseases. If small seeded vegetables are sown directly in the field,germination is often poor and the young plants grow very slowly and require a long time to mature. Also the season may be too short for full development in the field. To overcome these
problems many vegetable crops are grown in nurseries before being transplanted in the field. A
vegetable nursery is a place where plants are cared for during the early stages of growth, providing optimum conditions for germination and subsequent growth until they are strong enough to be planted out in their permanent place. A nursery can be as simple as a raised bed in an open field or sophisticated as a glass-house with micro-sprinklers and an automatic temperature control system. Although raising seedlings in a nursery has advantages, some vegetables do not transplant well, particularly root crops, and must be sown directly in the field for optimum results. It has to be noted, however, that transplanting seedlings interrupts their growth, which has the potential to reduce their vigor.
Advantages of growing seedlings in nursery beds.
Although many vegetable seeds can be sown directly in the field, experience has shown that raising seedlings in a nursery has a number of advantages as discussed below.
1. Intensive care - Seedlings receive better care and protection (from animals, weeds and pests)
in the nursery. The average garden soil is not an ideal medium for raising seedlings especially from the point of view of soil tilth. At an early stage of development most vegetable crops require special attention that is not possible in the main field.
2. Reduction of costs - Fewer seeds are used for raising seedlings in the nursery than for sowing
directly in the field,because in the latter seedlings have to be thinned to one, which is wasteful.
When expensive hybrid seeds are used, transplants therefore become more economically attractive. Pesticides and labour are also reduced under nursery conditions as compared to planting directly in the field.
3. Opportunity for selection - Raising seedlings in a nursery affords the grower an opportunity to select well grown, vigorous, uniform and disease free seedlings.
4. Extend a short growing season for late maturing crops - Seedlings can be raised in a nursery under a protected environment before conditions outside become suitable for growth and transplanted into the field when conditions allow, thus reducing the amount of time spent in the field.
5. Forced vegetable production for an early market - Generally prices of horthorticultural produce are attractive when production or supply is low. Vegetables can be grown ‘out-of-season’ in a nursery when conditions are not yet favourable. Such crops will thus mature earlier after transplanting and hence stand to fetch a higher price in the market.
Choosing a vegetable nursery site
A number of important aspects must be considered in choosing a site for the establishment of a
nursery if the outlay on seed, fertilizer, and labour is to show profitable returns. These factors are broadly grouped into the following:
1. Environmental factors
This refers to natural features of the land, which may greatly influence the cost of operation and
facilitate management of the nursery.
a) Proximity to planting site (main field) Some of the advantages of locating a nursery as close as possible to the main field are:
i) Cost of transporting the seedlings to the field is minimized.
ii) Less risk of loss of seedlings during transportation, and seedling failure after transplanting.
iii) Reducing the chances of transmitting or redistributing soil-borne pathogens through seedling roots or earth balls over long distances. When, however, particular diseases occur in the nursery area it may of course be advantageous to raise the seedlings outside the affected area in order
to initiate new plantings with disease-free seedling materials.
b) Land gradient (steepness of the land)
It is desirable to have the nursery on a level ground with good drainage. This will reduce the cost of establishing the nursery considerably. If the nursery is to be located on a sloping land, soil conservation measures are required, such as constructing terraces across the slope to conserve soil and moisture.
c) Nursery soils
Favourable soil conditions (good drainage, absence of toxicity, fertile, etc.) are indispensable for the success of a nursery. When nursery plants are raised in pots, polybags, seedboxes or trays, it may not be necessary for soils on the nursery site to be fertile. But in this case, a source of high quality soil must be as close to a nursery site as possible in order to lower the cost of soil transportation.
d) Water supply
A nursery should be located where a reliable, abundant and inexpensive supply of uncontaminated water is available. Water supply could be from wells, boreholes, natural streams or irrigation channels.
2. Proximity to services
a) Labour supply
Nursery operations are labour intensive, therefore, it is very important that nurseries are sited in areas where a dependable and regular supply of experienced labour can be easily obtained.
b) Markets
The nearness of nursery sites to potential buyers is very important to commercial nurseries intending to raise seedlings for sale to growers. Such a nursery should be located as close as possible to these growers.
c) Supplies
It is desirable to have a nursery located close to sources of inputs (equipments or tools, and consumables such as seeds, pesticides, fertilizers).
d) Services
It can be advantageous to have a nursery located in an area where the services of agricultural experts (horticulturists, crop protection specialists, soil scientists, etc) can be obtained easily.
Other aspects of services are the availability of good roads necessary for the transportation of supplies, seedlings and workers.
Types of nursery facilities
There are three main facilities normally used for raising seedlings in a nursery. The choice of a particular one will depend on the available resources and prevailing environmental conditions.
* Greenhouses - environment fully controlled
* Nethouse - environment partially modified
* Open field - where climatic conditions are normally favourable for the crops grown.
Media for raising seedlings
Soil is the major medium for germinating seeds and growing seedlings, although it is not the best. There are artificial media made of perlite, vermiculite and peat moss, which are used as soil substitutes. For best results, a growth/rooting medium should posses the following qualities:
- sufficiently firm enough and dense to hold seeds in place during germination.
- sufficiently porous to let excess water drain away
- have a high water holding capacity.
- free from weed seeds, nematodes and other pathogens.
- high cation exchange capacity so that it can provide nutrients
- able to withstand sterilization treatment without being altered.
- not be toxic to plants
Since it may not be possible for one medium to have all these characteristics, different media are normally mixed together to obtain a ‘near’ ideal mixture. Materials found in the locality may also be used. Some media may becontaminated, therefore it may be necessary to sterilize them before they are used, to kill weed seeds, insects and numerous soil pathogens. This treatment includes the use of heat and/or chemicals. Steam sterilization and solarization are used in the heat treatment to kill all pathogens in the media. One of the advantages of this treatment is that the media can be used sooner after treatment and the treatment can be applied to the dry, wet or even cold media.
There is, however, a risk of the media structure or composition being modified by the heat. Chemical treatment which is also referred to as fumigation involves the use of insecticides which may be specific to certain pathogens or broad spectrum (controls a wide range of pests). These chemicals should be handled with caution as most of them are toxic to both humans and animals. Some of the commonly used chemicals are, chloropicrim and vapam.
Seedling management
1) Watering. The seedbed or seedbox should be watered carefully with a fine stream of water.
After the plants are well established, watering should be done thoroughly but not too often. It is advisable to irrigate seedlings in the morning and not in the afternoon as the latter leaves the soil surface moist overnight, a condition favouring damping off.
2) Shading. Shading should be done to protect the young seedlings from high heat intensity in sunny areas and also from from heavy rain. Shade can be provided by polythene nets or even grass. The shade should be removed some days before transplanting to allow the seedlings to acclimatize to field conditions.
3) Thinning. This is a way of regulating plant density in rows and in holes. During thinning, weak,
diseased plants are pulled out to allow healthy seedlings to grow well. It is normally done when
seedlings have formed a few true leaves.
4) Insect pest and disease control. This is a continuous process from seedling emergence to
transplanting. It is normally done by physical means but chemicals can also be used if the
need arises.
5) Weeding. This is done by physical means when weeds emerge.
6) Hardening-off. Transplants must be ‘hardened-off’ so that they can withstand the transition from a relatively sheltered and protected environment to a sometimes harsh open situation. Generally, hardening is imposed from about 1 to 2 weeks prior to transplanting seedlings, by gradually exposing them to higher (or lower) temperature and the higher light intensity prevailing in the field. It should, however, not involve any treatment that may reduce the rate of photosynthesis, such as nutrient stress. Care should be taken not to over-harden plants, as this may delay maturity and in some instances even reduce crop yields.
7) Transplanting. This refers to the operation of lifting the seedlings from the seedbeds or containers and transferring them to the field where they will grow and mature. The main aim during transplanting should be to interrupt growth as little as possible, and if the operation is not carried out properly it can severely check growth or in extreme cases cause death of transplants. Most vegetable seedlings are ready to be moved 4-8 weeks after sowing. The seedbed should be given a thorough soaking about 6-12 hours before the plants are moved to ensure that they are fully turgid and that the roots retain plenty of soil when the plants are lifted. The main field should also be irrigated at the same time so that the planting holes can be opened up easily and the plants easily ‘firmed’. The best time to carry out transplanting is in the late afternoon or early evening, as this allows the plants some time to get partially reestablished before having to face heat stress during the day. A cool cloudy weather is ideal for transplanting. It is always wise to raise about 30% more seedlings than are actually required so that the weak ones can be discarded and any casualties replaced. The adaptability of vegetables to transplanting varies widely between crops. Transplanting success depends on how rapidly a plant is able to regenerate those parts of the root system that were lost/damaged during transplanting.
(Compiled by Harsh saxena)
