Choosing a seedling tray, and how to sow for reliable germination

Plastic seedling trays (also known as plug trays or pro-trays) of different sizes are available in the market. The selection of the seedling tray size by the nursery owner depends on local farmers’ preferences, but mostly, trays with 72 or 128 cavities (or plugs) are preferred.

Nursery owners have observed a better root growth in 72 cavity trays when the

temperature crosses 40°C during hot summer months.

There are two types of cavities in Marshine seedling trays available in the market: inverted cone shaped and inverted pyramid shaped.

The experiences of nursery entrepreneurs indicate that a tray with 128 cavities planting trays with an inverted pyramid shape is ideal for a strong stem and good root growth as it provides a wider space for the root system to grow. In contrast, the inverted cone shape narrows down the space for roots to spread, resulting in a cluster (Figure 20).

A seedling with a strongly developed tap root and secondary roots will establish in the main field faster than a seedling with a clustered root system.

Figure 10: Inverted cone shaped cavities vs. inverted pyramid cavities

The size of Marshine trays each cell is 30 mm x 30 mm wide x 40 mm deep, and the hole at the bottom of the cavity should not be less than 2 mm wide. Ideally, 20-40 cc of growing medium is required to fill each cavity.

When reusable seed nursery trays are used, they should be sturdier, with a minimum thickness of 0.8 mm. A seedling that is 25-26 days old with 4-5 true leaves is at the right stage for transplanting.

MANUAL METHODS OF SOWING

To maintain uniform sowing depth and speed, sow the seeds with the help of a manual seed dibbler (Figure 21) that pokes uniform holes in the medium. The recommended dibbling depth is three times the seed diameter.

Figure 11: Manual Seed Dibbler

While filling the Marshine seed trays, care has to be taken not to pack the cavities too tightly. It will stop aeration and lead to poor root growth, water accumulation and a higher EC of the medium, if there are problems with the quality of the water being used.

After sowing, a layer of vermiculite or finely sieved coco peat is spread on the sown seeds to a depth of 1-1.5 times the diameter of the seed. It will be easier for the seed’s epicotyls to push up through the light media while emerging.

MACHINE METHODS OF SOWING

In large scale nurseries a seeder assembly (Figure 22) can be used for automated tray filling, sowing, covering and watering. This enables about 90-100 trays to be filled in an hour.

Figure 12: Automatic seeder

CARE TO BE TAKEN AFTER SOWING

Whether in small-scale or larger well-established nurseries, it is important to transfer the seed propagation trays to a darkened germination room / closed chamber that is kept at a mild temperature. If small-scale nurseries do not have space for a separate germination room, one of the corners may be closed off and used for the purpose.

Stacking many trays on top of each other is generally not recommended, as the top ones will compress the trays beneath. If the germinating trays need to be stacked due to space constraints, it is recommended to use a zigzag arrangement where the upper tray does not directly touch the media of the lower tray (Figure 23).

Figure 13: Arrangement of sown trays

Tomato seeds germinate in 96 hours. Until then, the germination trays may be wrapped in a white polythene cover to maintain darkness and humidity. After 3 or 4 days, they will then have to be uncovered and the trays kept separate for uniform germination.

Figure 14: Cover Maintain Darkness Humidity

LABELING THE TRAY

It is important to label the trays to keep track of seedling production and reassure customers.

These sort of details have been successfully used in tray labels (Figure 24).

1. Tomato variety

2. Batch No.

3. Date of sowing

4. Date of dispatch

5. Company name

6. Contact no. & place

For example:

Figure 15: Label on the trays