Starting your own plants from seed will often give you healthier plants at a lower cost.  If you want to start seeds in bulk, you may want to consider a seed tray to help with germination.

So, what is a seed tray?  A seed tray is a container used to sow multiple seeds at once.  After seed germination, seedlings grow in the seedling tray until they are large enough for transplant.  A single seed tray can hold anywhere from 6 seeds to over 1000 seeds!

Of course, when choosing a seed tray, there are lots of options for the material, the type of tray, and the number of cells.


In this article, we’ll talk about seed trays and the options that are available.  We’ll also get into how to use seed trays and how to water the seeds and seedlings.

Let’s get going.

What Is A Seed Tray?


A seed tray is a container that is used to plant multiple seeds at once.  A seed tray is sometimes called a seed starting tray.


 A seed tray allows you to plant many seeds together in one container.  This makes it much easier to water them and transport them.


After the seeds germinate, the seed tray holds seedlings as they grow, until they are ready for transplant outdoors or into larger containers.


There are a few different types of seed trays, including:


Mesh seed tray – a mesh seed tray allows water to drain out easily.  A mesh seed tray is best for holding multiple individual containers (pots).  A drawback is that the holes in a mesh seed tray are too large to hold soil without it falling through or washing away when watered. You can find mesh seed trays from Johnny’s Selected Seeds.


Solid seed tray with drainage holes – a solid seed tray with drainage holes allows for adequate drainage, but allows soil to stay moist enough for seed germination.  A solid seed tray with drainage holes is best for planting multiple seeds together in one place.  A drawback is that the seedlings do not have individual cells, so their roots can get tangled together as they grow. You can find solid seed trays with drainage holes from Johnny’s Selected Seeds.


Solid seed tray without drainage holes (leak proof seed tray) – a solid seed tray without drainage holes does not allow for any drainage.  A solid seed tray without drainage holes is best for holding a cell flat (also called a plug flat).  Since it holds water, it can be used to catch excess water from watering seeds, or it can be used to water from below (more detail on this later). You can find cell seed trays without drainage holes from Johnny’s Selected Seeds.

Another interesting option is this seed flat with 20 rows from Johnny’s Selected Seeds. Instead of separate cells, there are separate rows to keep different plant varieties from getting mixed up.


If you decide to use a cell flat for seed germination, each cell should have its own drainage hole.  The tray below the cell flat should be solid without holes if you want to water the seeds from below.


The main problem of adapting the SRI techniques is high labor requirements for manual and lacking of mechanized system for planting single seedling in the field. The existing seedling preparation methods remain challenging among SRI practitioners due to traumatic condition. This study was intended to create modern techniques for increasing the quality and transplanting potentials to improve seedling preparation and reduce transplanting shock. It involved development of rectangular tray having 924 square growing cavities with sliding base to facilitate seedling transfer. Seed selection was conducted and 100% germination was obtained from the sunken MR219 seeds collected in 80 g/L of NaCl solution. SRI-tray seeding was 100% placed into cavities with SRI-seed picker at 150 g/L of tapioca solution. Two different media (Soil + Burnt husk (1:1) as M1 and Soil + Compost (1:1) as M2) were used to evaluate the growth performances for 10 days. The measured parameters (Seedling Height (SH), Leaf Length (LL), Leaf Number (LN), Root Length (RL) and Loosening Index (LI)) were compared between SRI-tray and conventional ones. The SAS revealed that M2 on SRI-tray had the highest significant values for SH, LL, RL and LI with the mean values of 155.6, 109.3, 89.3 and 75 sec when compared with conventional tray which had 125, 91 and 52 mm with no LI, respectively. The seed rate, nursery area and seedling age to support one hectare of planting area were found as 5.34 kg, 36 m2 and 8-10 days on SRI-tray against 15-50 kg, 250-500 m2 and 12-30 days on conventional practices.

The more pellets that are placed in the mould, the denser and stronger the seedling tray with lids.


In cheaper trays, there tend to be slightly bigger gaps between the expanded pellets, and fine plant roots can enter these, making it difficult to pull out the plants.

Damping off organisms can also lurk in these small spaces, and the growing plants can become infected and die. One of the Pythium species (fungus-type pathogens) is usually the main culprit, but it’s not the only one.

I have used horse manure compost as a medium for 23 years and have never had damping off problems. This may be because the medium is a rich source of beneficial organisms, which suppress development of pathogens. I also never get powdery mildew on Brassica seedlings.

Once the pathogen has appeared, the trays must be sterilised, or the problem will keep cropping up and possibly cause major losses.


The most effective way of sterilising trays is in a heat chamber. To save cost and effort, some growers wait until damping off starts before using heat sterilising.


Another solution is to use a commercial dip containing copper; this will also reduce the penetration of roots into the fine gaps in the polystyrene.


If you are a small grower, you can use a simple, home-made steriliser such as bleach mixed with water at a 10% solution, or hydrogen peroxide at 3% concentration. Leave the trays suspended in the solution for 20 minutes, then rinse and dry them.


The ideal sealant


One of the most effective ways of treating seedling trays is to dip them in a water-based roof paint when they are still new.


Obtain a flat receptacle slightly larger than the tray and dilute the paint with 10% water. Push the tray face down into the paint until the paint reaches the drainage holes. Lift and allow the excess paint to drip back into the tray, then place it face-up to dry. (It’s unnecessary to paint the base.) You should be able to coat about 10 trays per litre.


Some farmers are put off by the price of paint, but this treatment is well worth the cost: not only does it extend the life of the rice seedling tray by many years, but it seals the fine gaps in the polystyrene.


This reduces the risk of pathogens lurking in these crevices and also makes it much easier to pull out the seedlings.


Roof paints come in many colours, so you can use different colours for different years to keep track of the lifespan of each batch of styrofoam seed trays. There are often specials on roof paints and you can take advantage of these to cut the costs of the treatment.


Biodegradable plastics have been widely introduced into agricultural production, but their impacts on the soil ecosystem remain unclear. The present study investigated the impacts of a biodegradable seedling tray (BST) on the microbial communities in paddy soils. A 110-day rice culture experiment was conducted with three different paddy soils developed from black soil (BS, black chernozem soil), chao soil (CS, Fluvo-aquic) and red soil (RS, Alfisols) and three application rates of BST (0, 0.02 and 0.2?g?kg?1). Soil phthalic acid ester (PAE) concentrations, physicochemical properties and enzyme activities were determined to evaluate the influence of BSTs on soil quality. 16S high-throughput sequencing was used to study bacterial community composition and the Biolog EcoPlate? test was used to profile microbial activity and community function. Results show that the application of BSTs did not markedly affect soil quality, and the potential release of PAEs from BSTs was negligible. Interestingly, the microbial community was affected by BSTs in a soil-dependent and time-dependent pattern. The microbial community in RS was not significantly influenced by BSTs. Relative abundances of some predominant genera in BS (e.g. norank_f__BSV40) and CS (e.g. Norank_f__Nitrosomonadaceae) were significantly influenced by BSTs, and db-RDA results show that community composition in BS and CS was shaped mainly by BSTs. Community level profiling shows that BSTs significantly increased microbial activity and decreased functional diversity in BS after 55?days, but the impacts disappeared after 110?days. The results contribute to the knowledge of how biodegradable plastics influence microbial communities in paddy fields and provide information relevant to the practical use of BSTs under field condition.

This experiment investigated the effect of different plug-tray cell designs on root development of red maple (Acer rubrum), red oak (Quercus rubra), and quaking aspen (Populus tremuloides) seedlings. In April of 2015, seeds of each species were sown into three plug trays with different substrate volumes and grown for 17 weeks. Two trays had permeable walls for air-pruning, one with vertical ribs and one without. The third tray had impermeable plastic cell walls. Harvested seedlings were analyzed for root dry weight, length, volume, surface area and number of deflected roots. Root length per volume was highest in the impermeable-walled tray for red maple and quaking aspen. The total numbers of deflected root systems were higher for all species in the impermeable-walled tray. Seedlings grown in the air-pruning trays had smaller proportions of deflected root masses. Greater substrate volume did not influence root deflection development. The air-pruning tray without vertical ribs had the lowest total number of root masses with misdirected roots and lower proportions of root masses with misdirected roots for all species. These results indicate that improved root architecture in root-air pruning tray designs is achievable in tree propagation; however, vertical plastic structures in air-pruning trays can still cause root deflections.