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How to start vegetable seeds in an apartment

Transplants need more light and more weeks than a tray of microgreens. The setup is still a shelf, not a yard.

By Ryan Moalemi. Updated November 9, 2026.

You can start vegetable seeds in an apartment if you give them a sterile mix, a pot with holes, and stronger light than a microgreen tray needs. The plants are transplants. You will move them to a balcony pot or, if you have one, a garden bed. Steve Reiners at Cornell says the most important factor is light, and that even a sunny south window is not enough in quantity or quality to raise sturdy transplants. That single point separates this job from windowsill microgreens, which several extensions say can finish at a bright window because they are cut young.

This guide follows Cornell, a Seneca County Cornell Cooperative Extension handout by Lori J. Brewer, UC Cooperative Extension offices in Marin and Sonoma counties, and the University of Massachusetts planting-chart page for local timing. It is a method, not a record of seedlings grown for this article.

Photo coming soon. Cell packs of tomato and lettuce seedlings under a lamp on an apartment shelf, with the lamp a few inches above the leaves.
Photo coming soon. Planned photo: seedlings under a lamp a few inches above the leaves, on a shelf.

What to start indoors, and what to sow outside

Warm-season fruiting crops are the reason to start indoors in a short summer. Brewer's handout says tomatoes, peppers, and eggplants are often started about 6 weeks before you expect to transplant, and cucumbers, melons, and squash about 3 weeks before, because they grow fast and resent a long wait in a small pot. Reiners makes the same point with a cautionary calendar: for a last frost around May 20 in his example, tomatoes are sown indoors from about April 10 to May 5 for outdoor planting around May 25 to June 20, while summer squash needs only about three weeks of a head start. His table is built for that May 20 frost. If your frost is earlier or later, slide the dates. Do not copy a New York May date onto a different climate and call it local.

University of Massachusetts Extension publishes a vegetable planting chart for Massachusetts sowings and transplant dates. Use a chart for your own state when you have one. The skill is the same: count back from the outdoor date, and do not start so early that plants stall in the pot.

UC Marin Master Gardeners say eggplant, peppers, and tomatoes are better planted as seedlings because of their germination needs, while beans, beets, carrots, cucumbers, lettuce, peas, radishes, and summer squash can go in a container as seed or as seedlings. If your only outdoor space is a balcony planter, you can direct-sow the quick crops there and use the apartment shelf for the slow fruiting ones. Lettuce started indoors is possible. Reiners lists it. It also grows well from seed in the pot if the weather is cool enough, which is the balcony salad path.

Light, heat, and mix

Reiners's setup is a fluorescent fixture kept about 4 inches above the leaves, raised as the plants grow, on for 16 to 18 hours with a 6 to 8 hour night. Brewer's handout says that even a bright south window may need extra light, and suggests keeping lamps about 3 to 6 inches above the seedlings for 12 to 16 hours. The two Cornell sources are a few inches and a few hours apart. Both put the lamp close, for a long day. A lamp across the room is not the recommendation.

Heat is for germination, then you ease off. Reiners says many seeds do not need light to sprout, so a warm dark spot works until they emerge, and that running about 10°F above the later growing temperature can speed germination. After emergence, he uses the daytime targets in his table (about 65 to 75°F depending on the crop) and about 10°F cooler at night so plants stay compact. The Sonoma County master gardener handout says about 65 to 70°F by day and 55 to 60°F at night once seedlings are up, and it says seed germinates best in a steady soil temperature somewhere between 75 and 90°F, with the packet as the specific guide. A heat mat is optional in both Cornell pieces. It is not a substitute for the lamp after the seed is up.

Use a bagged seed-starting mix, not soil from outdoors. Reiners says garden soil can carry disease and drains poorly, so seed rots. The Sonoma handout says the same. Fill clean pots that are about 3 inches deep in Brewer's supply list, with holes in the bottom. Reiners accepts cell packs, cups, and cartons if they drain. Cornell and the Sonoma page are enough to set the container rules without adding a second climate's frost dates.

Steps

  1. Pick the outdoor planting week from a local frost date, then count back. Six weeks for tomato, pepper, and eggplant, and about three weeks for cucumber, melon, and squash, is the Brewer rule of thumb. Slide it with your climate. Write the crop and the sow date on the pot. Brewer suggests a pencil and a marker because memory does not last six weeks.
  2. Moisten seed-starting mix before it goes in the pot. Sow at the depth on the packet. The shared Cornell and Sonoma rule is about 2 to 3 times as deep as the seed is wide, or 2 to 4 times in the Sonoma wording. Tiny seed is barely covered. Sow a few extra because not every seed germinates. You will thin later.
  3. Water gently. Brewer says to mist, or to set pots in about an inch of water for no more than an hour, then drain. The Sonoma handout says you can set containers in an inch of warm water and then drain them, and that they should not sit in water all the time or the seed rots. That is the same habit as bottom watering, with a stricter time limit than people use on a microgreen tray.
  4. Keep the sown pots warm and out of direct sun until you see seedlings. Then move them under the lamp the same day. Long pale stems in the first week usually mean the lamp is too far or the day is too short, not that the variety failed.
  5. Thin when plants have two true leaves, to one plant per pot or about every 1.5 inches, which is Brewer's line. The Sonoma handout says to handle seedlings by the leaves rather than the stems. Feed with a half-strength soluble fertilizer once that second set of true leaves is there. Both handouts say half strength. Do not start fertilizer on the day you sow.
  6. Harden off before the balcony or the ground. Brewer says not to rush plants outside, and to prepare them for about a week or two. The Sonoma handout describes about two weeks: days outside in a sheltered spot, nights inside at first, then full nights out, with slightly less water. Transplant on a mild day. Set most seedlings at the same depth they grew in the pot. The Sonoma page notes that tomatoes, squash, and cucumbers can be set deeper, up to the first true leaves, because the buried stem can root. Do not bury the growing point of a lettuce plant the same way.

Apartment limits

Sow fewer plants than the shelf can light at 3 to 6 inches. Reiners's warning, and Brewer's, is that plants started too early outgrow the indoor spot. Small plants catch up. Leggy ones often do not. If you reuse cups, Brewer says to clean them with a 10 percent bleach solution and rinse. Start in fresh mix.

Microgreens can run on the same shelf as a separate tray with a different sowing density and a different harvest. Do not thin a microgreen tray to one plant, and do not eat your tomato seedlings as microgreens unless you meant to grow tomato microgreens on purpose. The methods share water-from-below and a soilless mix. They do not share seed rate or time. The dense method is microgreens in a small apartment.

FAQ

Can I start tomatoes on a windowsill with no lamp?

Cornell sources say no if you want sturdy transplants. Reiners says a south window is not enough. Brewer says even a bright window may need supplemental light, with lamps a few inches above the leaves for 12 to 16 hours. A window is a better fit for a short microgreen crop than for a six-week tomato.

How early should I sow?

Count back from your outdoor planting date. About six weeks for tomatoes, peppers, and eggplants, and about three weeks for cucumbers, melons, and squash, is the Cornell handout's guide. Shift the date for your last frost. The UMass planting chart is an example of a state-specific calendar, not a national one.

What mix should I use in an apartment?

A sterile, soilless seed-starting mix. Cornell and the Sonoma County handout both say to skip garden soil because it stays wet and can carry disease. Pots need drainage holes. A tray under them catches water so the shelf stays dry.

When do I fertilize seedlings?

After they have a second set of true leaves, at half strength, according to the Seneca County Cornell handout and the Sonoma County handout. Do not feed unsprouted seed. Microgreen trays are different: Maryland says they do not need fertilizer at all because you harvest so soon.

Sources

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