Seed Paper Pot Size: What Works for Seedlings and Cards

For starting seeds, a paper pot about 7.6 cm (3 in.) deep is a sound default, and it should have a drainage hole. If you want the plant to stay in the paper pot for a while, go much deeper, 15 to 30 cm (6 to 12 in.), with thick walls. If you are planting a seed paper card, any pot with drainage and a few centimetres of soil will do, because the seeds sit just under the surface.

“Seed paper pot” can mean two different things, and both are covered here. Some people want a pot made of paper to start seeds in. Others have a plantable card and want to know what container to put it in. Either way, the size question comes down to roots, water and timing.

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TL;DR

  • Seed-starting containers about 7.6 cm (3 in.) deep with drainage are a good default, according to the University of Saskatchewan.
  • A paper pot meant to hold a growing plant should be 15 to 30 cm (6 to 12 in.) deep with thick walls.
  • Homemade pots need a mold at least 5 cm (2 in.) deep and a small drainage hole in the bottom.
  • For a plantable card, size matters less than drainage and a thin cover of soil.
  • Move seedlings on once true leaves appear and the weather is warm enough.

Table of Contents

Two meanings of “seed paper pot”

It helps to separate the two before you pick a size.

A pot made from paper. This might be a folded newspaper pot, a pulp pot you mold yourself, or a store-bought paper or peat-style pot. You fill it with soil, sow a seed, and later plant the whole thing or peel it away. Iowa State University Extension notes that folded newspaper pots are suitable small containers for starting seeds, and that they can go into the ground with the seedling because the paper decomposes.

Seed paper in a pot. This is a plantable card or a sheet of seed paper with seeds already embedded. You place it in soil, keep it damp and wait. Here the pot is an ordinary container, and the paper is the seed source.

The next sections cover the first meaning in detail, then the second.

How deep and wide should a paper pot be?

How deep and wide should a paper pot be? — overview diagram

The most useful number comes from a Canadian source. The University of Saskatchewan’s gardening guide recommends seed-starting containers about 7.6 cm (3 in.) deep with good drainage. Shallower containers dry out quickly. Deeper ones use more potting mix and weigh more, which is a real consideration when you are carrying a tray of twenty pots from a windowsill to a porch.

A simple way to think about it:

Purpose Depth Notes
Starting seeds, then moving the seedling on About 7.6 cm (3 in.) Good drainage; the usual starter size
Homemade pulp pot (mold) At least 5 cm (2 in.) Washington State University’s minimum for the mold
Reusable rolled-paper pot About 8 cm wide and at least 8 cm tall Example from a Canadian home-gardening guide
Growing the plant in the paper pot for longer 15 to 30 cm (6 to 12 in.) Thick walls recommended

Width is the number most guides leave out. In practice, a pot about as wide as it is deep (the roughly 8 cm by 8 cm example above is a good picture) gives small roots room without leaving a large pocket of wet soil that never dries. A seedling in a very large pot sits in damp mix it cannot use, so resist the urge to go big on day one.

Small seeds, large seeds

One practical rule of thumb: tiny seeds such as lettuce, basil or poppies do fine in a shallow pot, since the plants stay small for weeks. Larger seeds and fast, leggy growers such as squash, cucumbers and sunflowers push roots down quickly and benefit from the deeper end of the range, or from an early move to a bigger pot. Check the seed packet for sowing depth and spacing, and size the pot to the first few weeks of growth, not the finished plant.

How to make a paper pot at home

There are two common methods. Both use paper you already have.

Pulp pot

Washington State University’s paper pot instructions are a good template:

  1. Tear up newspaper, or use at least three sheets of 8.5-by-11-inch paper.
  2. Soak the paper, then blend it into pulp.
  3. Choose a mold at least 2 inches deep, such as a small cup or jar.
  4. Press the pulp against the mold evenly, with no thin spots.
  5. Make a small drainage hole in the bottom.
  6. Let it dry in a warm place before taking it off the mold.
  7. Fill with soil to about 1 inch below the rim.

Thin spots are the usual failure. They tear when the pot is wet, so press a little more pulp in anywhere you can see light through.

Rolled or folded pot

A Canadian gardening group shows a reusable rolled paper pot about 8 cm across and at least 8 cm tall, made from a strip of paper 15 by 46 cm. The strip is long enough to wrap around the form twice, with about 8 cm of extra paper beyond the pot height to fold into the base. Their pots last roughly 30 to 40 days, which is plenty for most seedlings.

Rolled paper pot measurements and lifespan

If you are making pots for a classroom or a group of kids, the folded newspaper version is quick, and the paper wall is thin enough that roots get through easily.

Drying and handling

Wet paper is fragile. Handle full pots from underneath, not by the rim. Give them air circulation as well: the same Canadian guide warns that poor airflow can lead to mould on the outside of the pot, and that a pot that is too wet can tear or fall apart.

Watering paper pots without losing them

Paper wicks moisture, which is both the advantage and the catch. Washington State University recommends setting a saucer under the pot to catch water and keep it steady, and watering lightly into the soil rather than over the leaves.

Two more habits help:

  • Do not leave water standing. The University of Saskatchewan says drip trays make bottom-watering easier, but they should not stay permanently full because waterlogged soil starves seedlings of oxygen.
  • Cover the rim. For peat-type pots, the same guide says the rim should be covered by at least 1.27 cm (0.5 in.) of soil when planted out, since an exposed rim can pull moisture away from the roots. The same sensible step applies to any paper pot you bury.

The guide also notes that these pots suit plants that dislike root disturbance, such as melons and cucumbers.

Planting a seed paper card in a pot

This is the other half of the keyword, and it is simpler. A plantable card is made of recycled paper with seeds already in it. You are not sowing seeds one at a time, so you do not need a specific pot depth for sowing. You need three things: a container with drainage holes, decent soil, and a thin cover over the paper.

Our guides give a few specifics worth knowing:

Choosing the pot for the card

Match the pot to the seeds in your card:

  • Herbs and salad greens (basil, lettuce): a modest pot is fine. Our guides on growing a lettuce seed card and planting basil seed paper cover these two.
  • Flowers such as poppies: a wider, shallower container gives you a fuller display from one card.
  • Anything vegetable-sized: plan to move the seedlings into a larger pot or the garden once they have true leaves.

A card is also easy to fit to a small container. Tear it to fit, or plant it whole in a wide, shallow pot. If you are starting indoors in a Canadian winter, our guide to planting seed paper in winter explains why an indoor start beats waiting for a thaw.

When to move seedlings to a bigger pot

Timing matters more than the exact starter size. Washington State University says seedlings are usually ready to move to a larger container or outdoors once they develop true leaves, provided the weather outside is warm enough. True leaves are the second set, which look like a smaller version of the grown plant’s foliage, unlike the first rounded seed leaves.

You have two choices at that point:

  1. Plant the whole paper pot. Tear off the top edge so no paper sticks above the soil, and bury it with soil over the rim. Tearing a few slits in the sides helps roots escape.
  2. Pot up. Move the seedling into a larger container. For a long-term indoor home, a cork flower pot or any planter with drainage is a nice step up from a paper starter.

If your pots will stay indoors for longer than about a month, remember that a paper wall breaks down. The 15 to 30 cm depth with thick walls is the version meant for that.

Common mistakes with paper pot size

  • Going too shallow. A pot under about 7.6 cm dries out fast and needs watering more often.
  • Going too big. Extra soil stays wet around a tiny root system.
  • Skipping drainage. Without a hole, water pools at the bottom, however well the paper wicks.
  • Leaving the rim above the soil. Exposed paper acts like a wick and dries the root zone.
  • Keeping seedlings in the starter too long. Roots will circle or push through the wall. Move them when true leaves show.
  • Using laminated or glossy paper. Stick to plain newsprint or recycled paper. For seed paper cards, see our note on seed paper safety in Canada, which covers lamination and bleach.

Our view: size the pot to the first month

We make plantable cards, so we spend a lot of time talking to people about what happens after the card is opened. The most common worry is that they will do it wrong. Usually they will not. Seeds want a little soil, some moisture and light, and not much else.

Our advice on pot size is to stop overthinking it. Choose a container that is about as deep as a small yogurt cup, make sure water can drain, and put the seeds or the card near the surface. If you are using a paper pot, treat it as a starter that lasts about a month. When the plant has true leaves and the weather has warmed, give it more room.

We also like that a paper pot and a seed paper card end the same way: both go into the soil and become part of the garden. That is the idea behind every card we make, in Canada, from 100% post-consumer recycled paper, with non-GMO, non-invasive seeds inside. Nothing is left to throw away, and the person who receives the card gets to watch it grow.

— Trevor

A card that grows in any pot

If you would like to try seed paper without the guesswork, our plantable greeting cards come with an envelope made of recycled kraft paper and are blank inside for your own message. Send one to a friend, and they can tuck it into a small pot on a windowsill. Our shipping is plastic-free and compostable.

Poppy Flower Greeting Card

Browse our plantable greeting cards, or choose a theme: plantable wedding cards for a couple who will enjoy watching something grow, or seed paper valentines for a gift that lasts beyond the day. The Poppy Flower Greeting Card is a lovely one to start with, as flowers do well in a wide, shallow pot.

FAQ

What size pot should I use for starting seeds?

A container about 7.6 cm (3 in.) deep with good drainage is a reliable choice, according to the University of Saskatchewan. It holds enough soil to keep seedlings from drying out, without being heavy. Move seedlings on after they have developed true leaves.

Are paper pots good for plants?

Yes, for starting seeds. Paper pots let moisture evaporate through the walls and can be planted with the seedling, since the paper decomposes. They need careful watering and good airflow so they do not go mouldy or fall apart. A saucer underneath keeps them steady.

How do I make a paper pot for planting?

For a pulp pot, blend torn newspaper or three sheets of letter-size paper, press the pulp against a mold at least 2 inches deep, and add a drainage hole. Let it dry in a warm place before removing it. For a quicker option, wrap a strip of paper around a small can or jar and fold the end into a base.

What pot do I need for a plantable seed paper card?

Any pot with drainage holes works. Place the card, whole or torn, and cover it with a thin layer of soil, about 1 cm. Keep it damp and in a bright spot. If you grow a larger plant such as a vegetable, move it to a bigger pot once true leaves appear.

How long do paper pots last?

A homemade rolled paper pot lasts about 30 to 40 days, according to one Canadian gardening group. That is usually long enough to grow a seedling to transplant size. Pots meant for longer growth should be 15 to 30 cm deep with thick walls.

Sources

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