Last Updated on October 9, 2026

When to Pot Up Seedlings: Pot Size Chart by Crop

Start most seedlings in a single cell, then pot up tomatoes and eggplant into a 3- to 4-inch pot (9 to 16 square inches) about 2 to 3 weeks after they sprout; peppers go into a 4-inch cup at about 4 weeks. Lettuce, greens, broccoli and cabbage go up a size only if they outgrow their cell. Cucumbers, squash, melons and corn are the exception: sow them in the pot they will go out in and do not pot them up.

The sizes come from University of Maryland Extension, which recommends cells of 3 to 6 square inches for lettuce and other greens, 4 to 9 for squash, cucumber, broccoli and cabbage, and 9 to 16 for tomato, eggplant and pepper. The last column is how long each crop spends in a container on the Plan My Garden planner’s schedule.

Seedling pot size chart

Sources: cell sizes, the 2 to 3 week pot-up for tomato and eggplant, and “no potting up” for cucumber, squash, melons and corn are from University of Maryland Extension; the pepper schedule above is Tim’s own. “1 to 2 inches wider” and the onion flat are University of Minnesota Extension. Two true leaves and two seeds per peat pot for vine crops are Purdue Extension. The pepper pot-up schedule and container, and the lettuce container, are my own setup. Weeks in a container are arithmetic on the planner’s windows: for tomatoes, start 5 to 3 weeks before your last frost and plant out 2 to 3 weeks after it, so 5 to 8 weeks indoors.

Those planner windows are counted from your average last spring frost. Look up yours on the Plan My Garden frost dates page, or put it into the seed starting calendar to get the week for each crop.

Pot and soil block sizes compared

Maryland’s sizes are square inches of surface, so a square container is its width times itself. A 2-inch soil block is 4 square inches and a 4-inch block is 16, which is the top of the tomato range.

Arithmetic: 3½ x 3½ = 12¼. A round pot has about 79 percent of the surface of a square pot the same width (pi divided by 4), so a round 4-inch pot is about 12½ square inches, still inside the 9 to 16 range.

Soil blocks make the move up easy. I start in 2-inch blocks and move tomatoes into 4-inch blocks, which are made to hold the 2-inch block, so nothing gets pulled apart. Maryland Extension notes a 2-inch block is similar in volume to a large cell. The whole soil block method, mix recipe included, is on its own page. In cells, larger 3½-inch cups (affiliate link) work for up-potting tomatoes.

Signs it is time to pot up

• True leaves in a crowded flat. If you sowed many seeds in one tray, Maryland Extension says the ideal time to move them is shortly after the first true leaves appear above the seed leaves. It calls leaving seedlings in the flat too long one of the most common mistakes gardeners make, because crowded roots are hard to pull apart without damage.
• Leaves overlap, roots mat, or it stays wilted. Utah State University Extension lists three cues to pot up: leaves starting to overlap a neighboring plant, roots so dense they form a thick mat at the bottom of the container, or a seedling that seems perpetually dry and wilted between waterings. Lift it by the leaves to check the roots, or ease the root ball out before you blame watering; a mat of roots at the bottom, including roots showing through the drainage holes, is the same cue. In my seed starting guide, roots starting to circle the inside of the pot are the easy sign a seedling is outgrowing it, before it becomes rootbound.
• The weather holds you back. Penn State Extension notes seedlings outgrow their containers when cold or wet weather delays planting. That is when my peppers get their second move, into a 1-gallon pot. If the leaves themselves look wrong instead of just crowded, that is a different problem: check the seedling problems chart.

When you pot up, hold the seedling by a leaf, never the stem. University of Minnesota Extension says a seedling can grow a new leaf, but one that loses its main growing point may not survive. Purdue Extension says to set it at the same depth it was growing, except tomatoes: set them deeper, with only the leaves and growing tip above the mix, since they root along any buried stem.

Crops that hate root disturbance

Purdue Extension sorts vegetables by how well they move. Broccoli, cabbage, Brussels sprouts, lettuce and tomatoes transplant easily. Cauliflower, celery, eggplant, onion and pepper have a little slower root development. Cucumber, muskmelon, squash and watermelon do not transplant well and are seeded in individual pots.

For those vine crops, sow in the final container:

• Two seeds per pot. Purdue’s vine crop guide plants 2 seeds per peat pot, peat pellet or individual pot, thins to one strong plant at 2 inches tall, and needs only two to three weeks to reach transplant size.
• Plant out young. Purdue transplants cucurbits when they have two true leaves.
• Plant the whole thing. If you use peat pots, Maryland Extension says to remove the pot base and any rim above the soil line, because an exposed rim wicks moisture away from the roots. A soil block goes into the ground whole, which keeps root disturbance to a minimum.
• Start late in the window. The planner starts cucumbers 3 to 1 weeks before your last frost and squash and melons 2 to 1 weeks before, then plants them out 2 to 3 weeks after it. Starting at the late end keeps them closer to Maryland’s 2 to 4 weeks as a transplant.

Some crops should not go in a pot at all. University of New Hampshire Extension says root crops such as carrots and parsnips should never be transplanted, because transplanting damages the taproot, so sow them straight into the bed.

When the seedlings are ready to leave their pots, harden them off and follow my steps for transplanting seedlings into the garden and transplanting tomatoes. The full setup, from mix to lights, is in my guide to starting seeds indoors, and the pepper routine in the chart is from my guide to growing peppers from seed.

Know how long each seedling stays in its pot

The week you start and the week you plant out decide how big a pot you need. Plan My Garden is free to start: enter your zip code and it finds your frost dates, then builds a planting schedule with start indoors, transplant and direct sow dates for each crop. Draw your beds and pick your crops, and it places each plant at square-foot spacing, so you know how many seedlings to start.

Quick questions

What size pots should I start seedlings in?

University of Maryland Extension recommends cells of 3 to 6 square inches for lettuce and other greens, 4 to 9 for squash, cucumber, broccoli and cabbage, and 9 to 16 for tomato, eggplant and pepper. A 2-inch soil block is 4 square inches and a 4-inch pot is 16.

When should I pot up tomato seedlings?

About 2 to 3 weeks after they sprout. University of Maryland Extension says tomatoes started one per cell are moved into larger containers at that point. Set them deeper when you move them, because tomatoes root along any buried stem.

How much bigger should the next pot be?

University of Minnesota Extension says to use a container 1 to 2 inches wider than the cell the seedling outgrew. From a 2-inch cell or soil block, that is a 3- to 4-inch pot.

Should I pot up cucumber and squash seedlings?

No. University of Maryland Extension grows cucumber, squash, melons and corn for only 2 to 4 weeks as transplants with no need to pot them up. Sow two or three seeds in the cell or pot they will go out in and keep the strongest one.

How do I know a seedling is root-bound?

Lift it by its leaves and look at the bottom of the root ball. Utah State University Extension says it is time to pot up when the roots form a thick mat at the bottom. Roots starting to circle the inside of the pot are the other sign.

Related: Soil Blocks for Seed Starting · How to Start Seeds Indoors · How to Transplant Seedlings · Seed Starting Calendar · Seed Germination Temperature Chart