How to grow better seedlings


Every nursery desires healthy, vigorous seedlings. However, achieving this can be hard for newcomers and veterans alike. That said, you can utilize certain tricks to produce healthy trays. Here’s a friendly guide on how to grow better seedlings.

Start with the Seed

Choosing the correct seedling is crucial to growing a good seedling. The seed you use determines the germination, influences your sowing speed and accuracy, as well as the rate of growth of the seed and its disease resistance. As a living thing, the seed is shaped through many factors.

Seed can be purchased as:

  • raw seed
  • film-coated seed
  • pelleted seed

Alternatively, you might choose to collect your seed. Regardless, you’ll realise there are pros and cons to any seed you choose:

Raw Seed
Pros Cons
Generally the cheapest type of seed Can be shaped oddly (hairy, pointy or flat) which makes machining it into cell trays difficult.
This means some tray cells have no seed sown into them while others have doubles or multiples of seed.
Film-coated seed
Pros Cons
Possesses a thin film of chemicals that takes the edges off the seed, making it easier to sow. Some film-coats cause more scraping and wearing than others, depending on your seed’s shape, size, shape and seed-surface wax content.
Some seed suppliers have  developed film-coatings with excellent coating coverage, abrasion resistance and dust control, as well as very good flow and plantability properties The risk of abrasion also affects the rise to loss of active ingredients, detrimental to the seed protection efficiency and safety of seed treatment operators, growers and non-target organisms in the field
Pelleted seed
Pros Cons
Disguises the shape and size of the original seed, making it round and very easy to sow Often expensive because of the high cost of pelleting material, treatments, equipment, and time in the pelleting process
Vegetable seeds are often coated with different colours to distinguish them from each other Since pelleted seeds are so much larger than other seed-types, they take up more space.
The clay coating dissolves when the seedling is watered, enabling it to germinate Pelleted seeds do not last as long as other seeds because the chemical treatment reduces its lifespan
Allows very high-speed rotary drum seeding with high accuracy (in a machine like our range of automatic seeders  
Almost all cells will have one germinated seedling in them.  


An uneven fill across the tray often results in uneven growth. A fill that is too soft may mean that the plant doesn’t have much to grow on, and may stunt growth. And when it comes to transplanting, there is nothing worse for transplanting machines than a transplant without a good strong root mass, which needs a good fill to develop properly.

How to Store Your Seed

  • Store it at the right temperature. This depends on the seed type – your seed supplier will be able to advise.
  • Keep seed tin lids closed and packets sealed. Humidity has a great effect on your seed’s life and viability.
  • Read the information on the seed packet. This tells you what germination you can expect, the date of the seed’s germination test, its expiry date and other information. Some seeds have a low shelf life and need to be sown virtually straight away.
  • Keep records that track the seeds from the seed packet through the nursery. This alerts you to problems with the seed.

Using the right mix

Your seeding mix needs:

  • the right nutrients (for example, peat moss)
  • good moisture-holding capacity
  • the right density
  • flows easily when filling trays

Properly filling your trays

The quality of your fill determines the quality of your plant growth. Ideally, you want:

  • An even fill in each cell of the tray
  • A complete fill in each cell of the tray.

What happens if I unevenly fill my tray?

Simply put, an uneven fill results in uneven growth. Too soft a fill means your plants don’t have much to grow on, potentially stunting the process. The evenness of your fill also determines the strength of your root mass – a strong root mass is crucial for transplanting.

A quality, even fill ensures vigorous, even plant growth, easier transplanting, uniform field growth and a big harvest.

Our range of fillers help achieve even filling automatically. In our Universal Pot and Tray Filler, for example, the soil drops diagonally across the tray, smoothing out the soil into each cell via rotor, followed by a scraper and self-cleaning brush to remove soil from the cell dividers and prevent roots from growing cell to cell. The whole process is automatic, allowing you to fill your pots and trays at the touch of a button.

Using the right tray

The seedling tray you use has a profound effect on the quality of your seedlings and the viability of your business. A tray contributes to:

  • The density of plants, and thus the operating costs, in your nursery
  • The quality of the root structure of the plug, which in turn affects the quality of your harvest.
  • The suitability of the seedling to transplanting
  • The survival rate of your transplants in the field.

From a growing perspective, it’s all about cell shape. From a business perspective, the cost, durability, plant density, ease of cleaning, ease of handling and suitability to automatic transplanting are all important.


  • You don’t want spiralling roots, which don’t “take” as well when the seedling is transplanted, diminishing the vigour of the plant and increasing the likelihood it will be blown over in a strong wind.

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  • You don’t want a tray with a closed bottom which both causes root spiralling and reduces the amount of air that can come up from underneath and permeate the plug.

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  • You don’t want a square shaped cell which takes up a lot more area in your nursery for the same cell volume as a deeper, narrower cell. Square cells mean you get less plants in your greenhouse and spend more per cell on heating, watering and fertilising.

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  • You don’t want the transplant to stick in the tray when you go to pull it. Expanded polystyrene trays are notorious for roots growing into the cell walls. This means that the root is ripped off when the plug is pulled, damaging the seedling and also making it hard to clean the tray. Styrene trays are also notoriously hard to clean, and can carry disease with them.

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  • You don’t want cell walls that come in a lot towards a narrow bottom. This means that the roots don’t have much room to grow out into, diminishing the vigour of the seedling. Plugs from a tray with a small bottom are also hard to mechanically transplant. Since the base of the plug is so small when the plug falls into the kicker its tip may be squashed, making it hard to transplant at an even height.

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To grow good transplants you need a good cell like the one shown below:


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This cell, from the Williames 240 cell tray, has the following features which enable excellent transplants to be grown in it:

  • Sharp inside corners and a large open bottom, which prevent root spiralling.
  • A large, open bottom for good aerial pruning of the roots
  • A fairly deep cell, so you get more plants in your nursery. Compared with the Australian 198 cell tray, the 240 cell has exactly the same soil volume but you get 20% more plants into the same sized tray.
  • A rough inside texture, which helps stop water and fertiliser from running out down the sides and promotes aeration. However, the texture is not so rough that the plugs are hard to pull. Research in Holland and in California is also showing the importance of having a deep, reasonably narrow cell, which helps develop a thicker calliper on the stem. The photo below shows such a cell, from the Williames 224 cell tray – look at the stems of those plants!


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    Sow your seeds at the right depth, with accuracy:

    Every seed you sow has the potential to grow into a healthy, vigorous plant. However, to realise that potential, your seed must be placed at precisely the correct depth, in the centre of the cell, and with a minimum number of undesired doubles or misses.


    Place some seeds too deep – and the seed spends most of its energy just getting the radical to the surface, some seeds don’t make it at all

    Place a seed on the edge or corner of a cell and it can dry out and not germinate. If it grows its roots grow unevenly

    Place a seed in the centre at the right depth and the seed has ideal conditions for growing into a strong healthy seedling. Williames timed dibber and seed drums get the seed in the right place

    Place more than one seed in a cell (unless on purpose – eg shallots) and the nutrients in the cell are split between two or more plants. When excess plants are pricked out the roots of the remaining seedling are often damaged, stunting growth in the future due to transplant shock

    Miss planting a seed in a cell – and nothing grows, even with the best possible care of the tray after seeding. If say only 3% to 5% more live plants are grown this represents pure profit of 3% to 5% of total turnover as profit as all capital cost, soil, glass house space, heating and labour etc. is already covered


    The accurate placement of seed in the centre of the cell at the right depth is one of the critical factors on how to grow better seedlings. As discussed above, the seed type – whether raw, film coated or pelleted will greatly influence the accuracy of seeding.

    Williames Seeders give you full control over the depth of placement (it’s simple as well – just wind a handle up or down) and the conveyor, dibber and seed drum are mechanically connected and timed to give very accurate seed placement. By having at least 3 singulator bars (optionally 5) blowing in different directions to remove any doubles or multiple seeds you have high control over how many seeds go into each cell. The Williames Seeders enable you to give your seeds the best possible start.


Williames Pty Ltd
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103 Butlers Track, Warragul    Vic   3820
tel:        +61(3) 5623 5755
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