Prepping Pots and Trays for Planting

One of the biggest keys to success when planting seeds in pots / cell packs / trays is having a pot that is a suitable size for what you’re planting.

A common mistake is planting seeds in pots that are too small. It looks like the tiny seeds won’t need much room to grow - but it’s more important to consider how much soil and space they will need in the next 3 - 5 weeks of growth.

Trays are usually a standard size (approximately 10” x 20”), and the pots / inserts are named according to how many fit in a standard tray. The lower the number, the bigger the pot. A 38 cell tray fits 38 plants in a tray, whereas a 200 cell tray fits 200 (very tiny plants with almost no soil) in the same size of tray.

Some of the standard sizes are:

  • cell trays: 38, 72, 128, 200 plants per tray

  • cell packs:

    • 606’s … 6 cells per pack x 6 packs per tray = 36 plants per tray

    • 412’s … 4 cells per pack x 12 packs per tray = 48 plants per tray

    • 612’s … 6 cells per pack x 12 packs per tray = 72 plants per tray

You don’t really have to know the above info, unless you’re buying new trays or cell packs.

For most vegetables and herbs, I would recommend planting in a 72-cell tray at a minimum, and preferably pots that fit 36/ 38 / 48 plants per tray.

In other words, avoid tiny pots for your plants, and plant your seeds in (relatively) bigger pots.

You don’t have to go out and buy a specific size - you can re-use pots that you bought plants in from a nursery, or maybe you know someone who has a stash of extras in their garage.

Advantages of using bigger pots:

  • the plants will have adequate room to grow a sizable root

  • avoid the need to pot them up into a bigger pot… they can go directly from their original pot that you planted in, straight to the garden

  • the bigger pots will hold more water than smaller pots, and therefore require less watering

For an idea of size, the pots that are adequate for *most* varieties of vegetables are about 1 - 1.25 inches across and 1.5 - 2 inches deep.

“Fruiting” crops (such as tomatoes, peppers, melons, cucumbers) should be larger pots, at least 2 inches in diameter, up to 3 - 4 inches in diameter.

To Fill Pots with Soil

  • Put some potting mix into a waterproof tub or bucket.

  • Add some water, and mix it around to begin to moisten the potting mix.

    • The amount of water needed will vary widely, according to the type of potting mix and how moist it is in the bag. Start off with approximately 5-10% (no need to measure exactly) of the volume of the soil mix - you can always add more! In fact, it’s better to add the water gradually, until the soil mix has the right amount of moisture.

      • Eg, if you start with about 5L of potting mix, start with approximately 1 - 2 cups of water

    • I’ve found that it’s easier to moisten the soil if the water can sit for a few minutes in the soil before doing a thorough mixing. This helps the soil begin to take up water. Once it is primed with a bit of water, it will accept more water much more easily.

  • Add worm castings, compost, minerals, or any other amendments, and stir them in. It’s easier to mix these in when the soil is slightly damp - not dry and not soggy.

  • Then add more water, until the mix is thoroughly wet… there should be no water in the bottom of the tub, and the mix should still be “fluffy”, not in a wet ball or heavy or soggy.

  • Scoop this mix into the pots, taking care to not compress the soil; gently spread the mix so that it fills every pot in the tray.

  • Gently tamp the tray on the counter or bench (lift it an inch or two, then let it fall to the counter). This will help settle the mix in the pots, and eliminate any air pockets.

  • Top up the tops of the pots with more mix, and swipe or brush across the tops of the pots to remove the excess.

Now your pots are ready for seeds! Check out this article for some planting tips.