Modern Techniques for Raising High-Quality Nursery Plants

The way nurseries raise seedlings has changed dramatically over the past few decades. Traditional open-bed nurseries, where seedlings were grown directly in the ground and uprooted at transplant time, led to significant root damage, high mortality, and inconsistent plant quality. Today, modern nursery techniques rely on purpose-engineered containers, soilless growing media, and controlled greenhouse environments to produce healthier, more uniform seedlings – with far less waste. Understanding these techniques is essential for anyone involved in commercial plant production or advanced horticulture.

The shift from soil to container-based nursery systems 🔗

The most fundamental change in modern nursery management is the move away from soil-based production toward containerized systems. Rather than growing seedlings directly in nursery beds, plants are now raised in molded trays and individual pots that give each seedling its own defined space. This shift gives nursery managers precise control over root development, moisture retention, and plant spacing – none of which is easily achievable in open-ground cultivation.

Container systems also eliminate several problems inherent to soil beds: weed pressure, uneven nutrient distribution, and soil-borne pathogens. As noted by the Greenhouse Management resource on seed production techniques, each seedling grown in its own container does not compete with neighboring plants for water and nutrients, and if a soil-borne disease attacks one cell, it remains confined to that specific cell rather than spreading across the entire nursery bed.

Types of containers used in modern nurseries 🔗

Modern nurseries use a range of container formats depending on crop type, scale of production, and the stage of plant development. The most widely used include molded trays, plug trays, and individual nursery pots.

Molded trays 🔗

Molded trays are multi-cell containers made from thermoformed or injection-molded plastic. They come in a range of configurations – typically fitting the standard 1020 flat size – and are available with cell counts ranging from 32 to 288 or more per tray. The choice of cell count matters: larger cells hold more growing medium and moisture, supporting faster development, while smaller cells pack more plants into the same footprint, which improves greenhouse space efficiency. According to the Ontario Ministry of Agriculture, larger transplant trays generally result in earlier-maturing crops, but they do come at a higher cost per seedling due to greater space usage.

The geometry of the cells is also significant. Square cells are generally preferred over round ones because they are deeper, allow for better drainage, and hold a greater volume of growing medium per cell. Many tray designs also incorporate tapered walls that guide roots downward, discouraging the circular root patterns (root-binding) that often develop in conventional pots.

Plug trays (pro trays) 🔗

Plug trays – also called pro trays – represent the most advanced form of container growing for nursery seedlings. According to ATTRA, the USDA-funded sustainable agriculture resource, plug technology has transformed commercial seedling production since the 1980s, and by 1998, over 81% of annual seedlings in the US were grown from plugs. A plug is essentially a containerized transplant with a fully self-enclosed root system, which is what makes it so valuable at the point of transplanting.

Research on modern nursery raising systems in vegetables confirms that plug trays ensure greater germination rates, improved seedling care, better survival, and more uniform growth compared to conventional methods. They also offer improved handling and storage – both on the farm and during shipping. Cell counts in plug trays typically range from 50 to over 800 per flat, with the appropriate size determined by the crop species and how long the seedling will spend in the tray before transplanting.

For crops that are especially sensitive to root disturbance – such as cucumbers, melons, squash, and pumpkins – 32-cell trays are recommended, as the larger cell volume encourages faster, more resilient root development. For smaller-seeded crops like lettuce, kale, or herbs, trays with 128 to 288 cells are a practical and space-efficient choice.

Individual pots and forestry trays 🔗

For larger seedlings, woody plants, and tree species, individual nursery pots and specialized forestry trays are used. Forestry trays from manufacturers like Stuewe & Sons are built with smooth-walled cavities, built-in root-training ribs to prevent circling, and bottom drainage and aeration features to maintain optimal moisture and oxygen levels at the root zone. These trays are compatible with benching systems and mechanized handling equipment, making them suitable for large-scale reforestation and restoration nurseries.

Growing media for container nurseries 🔗

In modern container nurseries, seedlings are not grown in native soil. Instead, specially formulated soilless growing media are used. These mixes are engineered to provide the right balance of moisture retention, aeration, drainage, and nutrient availability – without the pathogens, weed seeds, or inconsistent texture that come with field soil.

The most common components of nursery growing media include:

• Peat moss: According to the University of Florida IFAS Extension, peat moss is the most widely used base ingredient in soilless mixes. It decomposes slowly, holds large amounts of water, and has a slightly acidic pH – lime is typically added to bring the pH to a suitable range for seedling growth.
• Coconut coir: A by-product of coconut fiber processing, coir behaves similarly to peat moss in terms of moisture retention but is pH-neutral and has natural resistance to fungal and bacterial pathogens. It is increasingly used as a sustainable alternative to peat.
• Perlite: A lightweight, pH-neutral volcanic material, perlite improves drainage and aeration in growing media by creating pore space for air and water movement. It is sterile and disease-free, which is critical in seedling production.
• Vermiculite: A heated mineral that expands into porous particles, vermiculite improves both moisture retention and aeration. It has a relatively high cation exchange capacity, allowing it to hold and release nutrients for seedling uptake.

ATTRA’s guidance on potting mixes notes that many modern nursery media use a combination of peat moss (or coir), perlite, and vermiculite at roughly equal proportions, sometimes with the addition of compost for biological activity. The key is maintaining adequate air space – overwatered or compacted media reduces the oxygen available to roots and increases disease risk. For plug trays specifically, the growing medium should be moistened before filling so that air porosity is maintained, with a moisture content of approximately 45-55% by weight at seeding.

Plug trays in greenhouse environments 🔗

While plug trays can be used in shade-net structures and low-cost nursery setups, they are most effective when combined with a greenhouse environment. Greenhouses – whether made from glass, polyethylene film, or polycarbonate panels – provide protection from weather extremes, pest pressure, and environmental stress. Inside, temperature, humidity, light, and irrigation can all be managed with a level of precision that is impossible in open-field conditions.

Within a greenhouse, plug trays are typically placed on raised benches that allow for good air circulation beneath the trays. This prevents waterlogging, reduces the risk of fungal diseases, and keeps the root zone at a consistent temperature. Automated or semi-automated irrigation systems – overhead booms or sub-irrigation reservoirs – ensure that all trays receive uniform watering, which is critical for achieving consistent seedling development across the entire batch.

The University of Georgia Cooperative Extension emphasizes that sanitation within greenhouse transplant systems is non-negotiable. Trays should be disinfected between crops using chlorine bleach solutions or registered disinfectants, and the water supply should be free from pathogen contamination. These practices protect the high density of seedlings from disease outbreaks that could rapidly move through an entire greenhouse batch.

Nutrient management in plug tray greenhouses also follows a more precise protocol than traditional nurseries. Research on plug tray systems indicates that complex fertilizer solutions with micronutrients are typically applied daily to maintain optimal seedling nutrition. Monitoring electrical conductivity (EC) and pH of both the water supply and nutrient solution is recommended, as high EC or incorrect pH can directly impair germination and root development.

Reducing transplant shock with modern techniques 🔗

One of the most significant practical advantages of modern container-based nursery techniques is their ability to minimize transplant shock – the stress that plants experience when moved from a nursery environment to the field. In traditional bare-root production, seedlings are yanked from the soil, causing significant root damage and loss of the moisture-retaining rhizosphere around the roots.

In plug tray systems, the entire root ball moves intact with the seedling. Greenhouse Management’s transplant production guide notes that transplanting from plug trays is fast and easy, with very little transplant shock occurring, and the seedling establishes itself rapidly in its new container or field position. This is especially important for crops with delicate root systems.

However, seedlings raised in the controlled warmth and humidity of a greenhouse still need to be hardened off before going into the field. Hardening off is the process of gradually acclimatizing plants to outdoor conditions. Michigan State University Extension explains that this is achieved by progressively reducing irrigation frequency and gradually lowering greenhouse temperature by 5 to 10°F over several days. This process prepares the plant’s tissues for the wider temperature swings, wind exposure, and reduced humidity of the field, significantly reducing post-transplant losses.

Best practice guidelines from Ohio State University’s W. Garrett Owen, published in Greenhouse Grower, also recommend pre-irrigating plug trays two to three hours before transplanting to make plug removal easier and reduce the risk of root damage during handling. Once removed, plugs should be supported by the root ball – not the stem or foliage – to avoid mechanical damage that can delay establishment or invite disease.

Benefits of modern nursery techniques at a glance 🔗

The adoption of modern container-based nursery systems delivers clear, measurable advantages over conventional methods. Uniform cell sizes within plug trays ensure that every seedling receives the same volume of growing media, the same moisture level, and the same root development conditions – leading to synchronized growth across an entire batch. This uniformity is especially valuable for commercial growers who need large numbers of transplant-ready seedlings at the same time.

Beyond uniformity, modern techniques support off-season and year-round production. Protected structures and controlled environments allow nurseries to raise crops during periods of unfavorable weather, extending the productive calendar. Plug tray systems also reduce seed requirements – since each seed is placed individually in a cell, there is far less wastage compared to open-flat broadcasting methods. And because seedlings are raised in a disease-managed, soilless environment, they arrive at the transplanting stage healthier and more vigorous than seedlings raised in conventional soil-based systems.

What do you think? As modern nursery techniques continue to advance, do you think smaller-scale farmers and home growers can realistically adopt plug tray and greenhouse systems – or are these methods primarily suited to large commercial operations? And with the growing interest in sustainability, how do you see the shift from peat-based to coir-based growing media shaping the future of nursery management?

References

1. https://www.greenhouse-management.com/greenhouse_management/plant_propagation_seed/greenhouse_seed_production_techniques.htm
2. https://www.ontario.ca/page/growing-vegetable-transplants-plug-trays
3. https://attra.ncat.org/publication/plug-and-transplant-production-for-organic-systems/
4. https://www.researchgate.net/publication/327390066_Modern_Nursery_Raising_Systems_in_Vegetables
5. https://stuewe.com/product-category/forestry-trays/
6. https://sfyl.ifas.ufl.edu/lawn-and-garden/homemade-potting-mix/
7. https://perlite.com/benefits-horticultural-perlite-commercial-greenhouses/
8. https://attra.ncat.org/publication/potting-mixes-for-certified-organic-production/
9. https://extension.uga.edu/publications/detail.html?number=B1144&title=commercial-production-of-vegetable-transplants
10. https://www.greenhouse-management.com/greenhouse_management/plant_propagation_seed/greenhouse_transplant_production.htm
11. https://www.canr.msu.edu/news/proper_transplant_hardening_off_may_be_a_deal_breaker_for_your_season
12. https://www.greenhousegrower.com/production/best-practices-for-spring-plug-and-liner-transplanting/