Comprehensive Guide to Raising Tasar Nursery: From Seed to Seedling

Tasar sericulture is one of India’s most important forest-based silk industries, providing livelihoods to over a lakh of tribal families across central and eastern India. At the heart of this industry lies the cultivation of tasar host plants – primarily Terminalia arjuna (Arjun), Terminalia tomentosa (Asan), and Shorea robusta (Sal). These trees serve as the primary food source for the tropical tasar silkworm, Antheraea mylitta Drury. Before these host plants can be established in the field, they must first be raised as healthy seedlings in a well-managed nursery. This guide walks you through the entire nursery-raising process – from seed collection and pre-treatment to seedling care and final transplantation.

Why nursery raising matters in tasar sericulture 🔗

In the wild, tasar silkworms feed on tall, irregularly distributed trees in forests. This makes it difficult to supervise the larvae, leading to high mortality from pests and diseases, especially during the early larval stages. Modern sericulturists prefer to cultivate food plants in systematic plantations for better supervision and higher foliage yield. To establish these plantations, strong and disease-free seedlings are essential – and that begins in the nursery.

Raising seedlings in a nursery allows you to control germination conditions, protect young plants from harsh weather and pests, and select the healthiest specimens for transplanting. Nursery-raised saplings of Terminalia arjuna, when closely spaced at 1.2 × 1.2 m, can become suitable for silkworm rearing within just three years and can yield over 17 metric tonnes of foliage per hectare.

Understanding tasar host plants 🔗

Before diving into nursery techniques, it helps to understand which plants you’re working with. The tropical tasar silkworm is polyphagous – it feeds on more than 51 species of host plants. However, eight primary food plants are most commonly used in commercial tasar culture.

Primary food plants 🔗

The most widely cultivated primary food plants include Terminalia tomentosa (Asan), Terminalia arjuna (Arjun), Shorea robusta (Sal), Lagerstroemia parviflora (Sidha), Lagerstroemia speciosa (Jarul), Lagerstroemia indica (Saoni), Zizyphus mauritiana (Ber), and Hardwickia binata (Anjan). Among these, Arjun and Asan are the two species most commonly raised in nurseries for plantation purposes.

Why seed propagation is the standard 🔗

Tasar food plants are typically propagated through seeds because they cannot be easily multiplied through vegetative (asexual) methods. While techniques like air layering, grafting, and stem cutting have been achieved on a limited scale for species like Terminalia arjuna and Zizyphus mauritiana, seedling propagation remains the most common and practical approach for large-scale plantation.

Seed collection and storage 🔗

Successful nursery raising starts with collecting quality seeds at the right time. For Terminalia arjuna, fruits typically ripen between February and May. Ripe fruits can be collected directly from trees or gathered from the ground below them.

How to collect and store seeds 🔗

After collection, the fruits should be dried in the shade for about a month. The fibrous ribs on the fruit surface can be reduced by rubbing them with your hands. Under proper storage conditions – such as dry gunny bags or sealed glass bottles kept in a cool, dry place – the seeds remain viable for up to one year. Some sources suggest viability can extend up to three years under ideal conditions, but for best germination rates, use fresh seeds.

It’s worth noting that every third year is typically a good seed year for Terminalia arjuna, so plan your seed collection accordingly.

Seed pre-treatment for improved germination 🔗

Tasar host plant seeds – particularly those of Terminalia arjuna – have hard seed coats that make water absorption difficult. Without pre-treatment, germination can be slow and inconsistent. Pre-treatment techniques help break seed dormancy and speed up the germination process.

Soaking and heaping method 🔗

The most widely practiced pre-treatment method involves two steps:

Step 1 – Hot water dip: Seeds are briefly soaked in hot water for about one minute. This softens the hard outer coat and makes the seed permeable to water.

Step 2 – Cold water soaking: After the hot water dip, the seeds are transferred to cold water and left to soak for 48 hours. This extended soaking ensures that the seed absorbs enough moisture to initiate germination. According to the World Agroforestry Database, the germination process for Terminalia arjuna takes 50-76 days, during which 50-60% of seeds typically germinate.

An alternative pre-treatment method involves covering the seeds with boiling water, allowing the water to cool naturally, and then soaking for 24 hours. Research from Pakistan has also shown that treating Terminalia arjuna seeds with gibberellic acid (GA) at 75 mg/l for 24 hours can significantly enhance germination rates.

Heaping for warmth and moisture 🔗

After soaking, the seeds are typically heaped together in a shaded area and covered with moist gunny bags or straw. This heaping process maintains consistent warmth and humidity around the seeds, which encourages the embryo to begin breaking through the seed coat. The heap should be checked regularly, and water should be sprinkled if the covering material dries out. Once the seeds show signs of germination – a small crack or emerging radicle – they are ready for sowing.

Preparing the nursery beds and polythene tubes 🔗

Once the seeds have been pre-treated and begun to germinate, the next step is sowing them into the nursery medium. For tasar host plants, polythene tubes (also called poly bags) are the most common containers used for raising seedlings.

Choosing the right polythene tubes 🔗

Standard polythene tubes for tree nurseries are typically around 10 cm in diameter and 20 cm deep, though sizes can vary depending on the species and the intended duration of the nursery period. The tubes should have drainage holes at the bottom to prevent waterlogging, which can cause root rot in young seedlings.

Preparing the soil mix 🔗

The soil mix used to fill the polythene tubes plays a critical role in seedling health. A commonly recommended ratio is 1:1:1 – that is, equal parts of garden soil, sand, and well-decomposed farmyard manure (FYM) or leaf mould. This mixture ensures good drainage (from the sand), adequate nutrient supply (from the FYM), and structural support (from the soil).

Before filling the tubes, the soil mix should be sieved to remove stones, clods, and debris. Some nursery practitioners also recommend treating the soil with a fungicide to prevent damping-off disease, which is common in nursery conditions.

Sowing the germinated seeds 🔗

Place one to two germinated seeds per polythene tube at a depth of about 2.5 cm (1 inch). The seed should be positioned with the emerging radicle facing downward. After sowing, gently cover the seed with the soil mix and press lightly. Water the tubes immediately after sowing using a fine rose can to avoid disturbing the soil surface.

The best time for sowing varies by region. For Terminalia arjuna, sowing is commonly done between February and March or during the onset of the rainy season, depending on local climate conditions. The tubes should be arranged on prepared nursery beds in a shaded area that receives filtered sunlight.

Watering and irrigation management 🔗

Water is the single most important factor in nursery success. Tasar host plant seedlings need consistent moisture – but not waterlogging – throughout their nursery period.

Watering schedule 🔗

Immediately after sowing, water the poly bags thoroughly. During the initial germination phase, water twice daily – once in the early morning and once in the late afternoon after 4:00 PM when the sun is less intense. As the seedlings grow and establish their root systems, watering can be gradually reduced to once daily.

During the rainy season, natural rainfall may be sufficient, and additional watering may not be needed. However, during hot summer months (May-June), irrigation should be more frequent, with watering done during the cooler parts of the day to minimise evaporation loss.

Signs of overwatering and underwatering 🔗

Overwatering leads to waterlogged soil, root rot, and fungal infections – especially damping-off disease. If the soil surface stays wet and slimy, reduce the frequency of watering. Underwatering causes wilting, yellowing leaves, and stunted growth. If the top layer of soil feels dry to the touch, it’s time to water.

Seedling maintenance for 2-3 months 🔗

After germination, the seedlings require careful maintenance for a period of 2-3 months before they are ready for transplantation. This phase involves weed control, pest management, thinning, and hardening.

Weeding 🔗

Weeds compete with seedlings for nutrients, water, and light. Regular manual weeding – at least once every two weeks – should be carried out in the nursery. Avoid using herbicides in the nursery as they can damage young seedlings. Pull weeds gently by hand to avoid disturbing the seedling roots.

Thinning 🔗

If two seeds were sown per tube and both germinate, remove the weaker seedling when the plants are about 5-7 cm tall. This ensures that the remaining seedling has adequate space and nutrients for healthy growth. Thinning should be done carefully to avoid uprooting the stronger seedling.

Shade management 🔗

Young tasar host plant seedlings benefit from partial shade during the first few weeks. A shade structure made from bamboo and grass or shade netting can reduce direct sun exposure. As the seedlings mature, gradually reduce the shade to expose them to more sunlight. This process, known as hardening, prepares the seedlings for the harsher conditions they will face in the open field.

Application of fungicides and insecticides 🔗

Nursery seedlings are highly vulnerable to fungal diseases and insect pests. Preventive and curative measures using appropriate fungicides and insecticides are essential parts of nursery management.

Fungicide application 🔗

The most common fungal threat in nurseries is damping-off disease, caused by soil-borne fungi such as Pythium, Fusarium, and Rhizoctonia. To prevent this, treat the nursery soil with fungicides like Captan or Thiram at a rate of 5-6 grams per square metre of nursery area before sowing. During the seedling growth phase, periodic spraying with a copper-based fungicide can protect against leaf spot and other foliar diseases.

In Terminalia arjuna, powdery mildew caused by Phyllactinia terminalae has been reported as a significant disease. Regular monitoring and timely fungicide application can keep this under control.

Insecticide application 🔗

Common nursery pests include leaf-rolling beetles, defoliating caterpillars, and termites. For soil-borne pests like termites, mixing insecticides such as Furadan or Heptachlor into the soil at a rate of 4-5 grams per square metre, up to a depth of 15-20 cm, provides effective control. For foliar pests, a mild neem-based insecticide spray at regular intervals can be used as a safer alternative.

It is important to note that seedlings treated with beneficial microorganisms like Burkholderia species during the nursery stage have shown enhanced shoot and root growth, which is an emerging area of interest in tasar host plant management.

Hardening seedlings before transplantation 🔗

About four weeks before the planned transplanting date, seedlings should undergo a hardening process. This toughens the plant tissues and prepares the seedlings for field conditions.

Hardening involves gradually reducing the frequency of watering and removing any shade cover so the seedlings are exposed to full sunlight. You can also withhold water entirely for short periods (1-2 days) to allow the soil to dry out and the seedlings to experience mild water stress. Hardened seedlings develop thicker stems, deeper roots, and more compact growth, all of which improve their survival rate after transplanting.

Transplanting seedlings to the main field 🔗

After 2-3 months of nursery care (or 8-9 months for larger planting stock depending on the species and purpose), the seedlings are ready for field transplanting. The ideal transplanting window is June-July, coinciding with the onset of the monsoon season, which provides natural moisture for the newly transplanted saplings.

Preparing the planting pits 🔗

Dig pits of approximately 30 cm × 30 cm × 30 cm at the desired spacing. For economic tasar plantations, a close spacing of 1.2 × 1.2 m is recommended. Fill the pits with a mixture of soil, 10-20 kg of FYM or compost, and 100-200 grams each of karanj cake, bone meal, and wood ash. This enriched pit provides the young plant with sufficient nutrients for the first year of growth.

Transplanting technique 🔗

Carefully remove the polythene tube without disturbing the root ball. Place the seedling in the prepared pit so that the root collar is level with the surrounding soil surface. Fill around the root ball with the pit mixture and firm the soil gently with your hands. Prepare a small basin around the base of each transplant to collect rainwater. Water the seedlings immediately after transplanting.

Post-transplant care 🔗

For the first two years after transplanting, the young trees need regular weeding and protection from fire and frost. Terminalia arjuna is initially a slow grower but picks up speed later, reaching 2-3 metres in height within three years. Pruning should be carried out to remove weaker shoots if frost damage causes forking of the stem.

Common challenges in tasar nursery raising 🔗

Several factors can affect nursery success. Being aware of these challenges helps you prepare better.

Low germination rates 🔗

Terminalia arjuna seeds have a natural germination rate of only 50-60%. To compensate, always sow more seeds than the number of seedlings you need. Proper pre-treatment significantly improves germination, so do not skip the soaking step.

Damping-off disease 🔗

This is the single biggest killer of nursery seedlings. It causes seedlings to collapse at the soil line. Prevention through soil treatment and proper drainage is far more effective than trying to cure an outbreak.

Termite damage 🔗

Termites can destroy seedling roots underground without any visible signs above the surface until the seedling suddenly wilts. Soil treatment with appropriate insecticides before sowing is the best preventive measure.

Inadequate hardening 🔗

Seedlings that are not properly hardened before transplanting suffer high mortality in the field. Ensure you begin the hardening process at least four weeks before the planned transplanting date.

The role of quality nurseries in tasar silk production 🔗

The quality of tasar silk production is directly linked to the quality of the host plant foliage. Strong, healthy trees produce more and better leaves, which in turn support better silkworm growth and higher cocoon yields. According to the Central Tasar Research and Training Institute, improving host plants through better nursery practices, germplasm selection, and plantation management is one of the key strategies for boosting India’s tasar silk production. Every improvement in the nursery stage cascades through the entire production chain – healthier seedlings lead to stronger trees, better foliage, more productive silkworm rearing, and ultimately, more and finer tasar silk.

What do you think? If you have access to tasar rearing areas, have you noticed differences in silkworm performance on nursery-raised plantation trees versus naturally growing forest trees? And given that Terminalia arjuna seeds have only a 50-60% germination rate, do you think more research into vegetative propagation methods could help scale up tasar plantations faster?

References

1. https://apps.worldagroforestry.org/treedb2/speciesprofile.php?Spid=18136
2. https://link.springer.com/chapter/10.1007/978-981-10-3304-9_10
3. https://silks.csb.gov.in/ranchi/wp-content/themes/Common_District/ranchi/fpptt-frame.html
4. https://innspub.net/a-response-of-tropical-tree-terminalia-arjuna-arjun-combretaceae-myrtales-seeds-and-seedlings-towards-the-pre-sowing-seed-treatment-in-forest-nursery-of-sargodha-pakistan/
5. https://www.cifor-icraf.org/publications/downloads/Publications/PDFS/MN15937.pdf
6. https://www.agrifarming.in/terminalia-arjuna-herb-farming-growing
7. https://www.semanticscholar.org/paper/Comparative-Study-of-the-Effect-of-Different-Food-Deka-Kumari/40609979473b5adee181c56d0369404a93df22a5
8. https://www.researchgate.net/publication/366371948_BREEDING_IN_HOST_TREES_OF_TASAR_SILKWORM_FOR_HIGHER_FOLIAGE_PRODUCTIVITY