Growing Seeds Indoors in Winter: What a Windowsill Can Do

Oct 22, 2026

Growing seeds indoors in winter is easier than most people assume. Your house is already the warm part. A heated living room sits right in the range most seeds want, so the sprouting end of this works beautifully in January. You need a windowsill and a little patience, and that is the whole list. No yard, no greenhouse, no equipment.

The one thing winter is short on is light, and that shapes what happens after the green appears. This matters because December is when grow kits get opened. Someone hands you a pot of herbs, you plant it that week, and the days are as short as they get all year. Here is how to make that go well.

Herb seedlings growing indoors in winter on a windowsill planter
A sill like this is plenty for sprouting. The taller, thinner growth afterward is the light talking.

Winter is on your side for sprouting

Most seeds germinate best somewhere around 65 to 75 degrees, which describes a normal heated room. The University of Georgia and Utah State both put the general range there. So for the first few weeks, your house is doing the work for you.

That is the part worth knowing before you start checking the pot twice a day. Warm room, a little water, and the seed gets on with it. The interesting stretch begins once the seedling is up and looking for light.

How much light do indoor seedlings actually need?

Extension services agree closely on this, and the figure is higher than most people guess.

Source Light per day for seedlings
University of Minnesota Extension 12 to 16 hours
Iowa State University Extension 12 to 16 hours
University of Maryland Extension 14 to 16 hours
University of Missouri Extension 14 to 16 hours
University of Georgia Extension 16 hours

A winter window gives you less than that. Short days, a low sun, and plenty of gray ones. The same sources say so directly. Iowa State notes that a sunny window usually does not give enough light. The University of Maryland points to a south facing bay window or a sun room as the comfortable case.

What that means in practice is mild. Seedlings on a winter sill still come up and still grow. They stretch taller and thinner than the same seed would in May, and that is mostly a question of looks. Plenty of people grow herbs on a January sill and never think about it again.

Why are my seedlings tall and thin?

Because they are reaching for the window. When light is short, a seedling spends its energy on stem length to get closer to the glass. The University of Minnesota names low light as the main cause of long, skinny stems. The University of Georgia describes plants growing spindly and leaning toward the window. Illinois Extension calls low light the most common cause of it.

Two other things add to it, and both are common in a heated house. Missouri Extension points to nights warmer than about 60 to 65 degrees, and to crowding. A dozen seedlings on a radiator shelf meet both of those at once.

The fixes, easiest first:

  • Turn the pot. Iowa State and UMass both suggest rotating seedlings in a sunny window so they grow straight. Free, takes a second, works.
  • Use the brightest glass in the house. South facing is the one every source names, and south or southwest gives the most. A north window asks the most of you.
  • Give them room. If several seeds came up in one small pot, keep the strongest. Snip the others at the base once they have a second set of leaves.
  • Add a lamp. This is the real answer if you want stocky plants in January. Extension recommendations for how close to hang it run from about 2 to 12 inches above the leaves. Most land between 2 and 6 inches. Iowa State, Minnesota and Georgia all sit in that band. Put it on a timer for 12 to 16 hours, and give plants a dark stretch at night rather than running it around the clock.
  • Let the room cool a little. The University of Georgia suggests easing the temperature toward 65 degrees once seeds have come up. Sturdier growth follows.
Lavender and chamomile seedlings on a windowsill planter in winter
Giving each variety its own section keeps the slow starters from being shaded by the quick ones.

How often should I water in winter?

Look every day. Water less often than you would in summer.

Both halves matter. Iowa State is clear on the first point. Once a seed has taken up water it needs to stay damp, so a pot left dry partway through germination will not finish. North Carolina State says the same. Checking daily takes five seconds and covers it.

The second half is the one that surprises people. The growing medium stays damp much longer in a cool room with no breeze, so winter watering is lighter than summer watering. Medium that stays soaked leaves roots short of air. Cool damp conditions also make room for the seedling rot that extension pages call damping off. Iowa State ties it to poor drainage, crowded pots and generous watering.

So the practical version: water when the surface feels dry to the touch, and water from below where you can. Set the pot in about an inch of warm water and let it soak up what it needs. North Carolina State and Virginia Tech both recommend that approach. For tiny seeds resting on the surface, a spray bottle keeps them where you put them.

If your kit came in a decorative pot with no hole, add one in the center. That is what our kit instructions suggest, and Illinois Extension and Virginia Tech give the same advice for any container without drainage. Gravel in the bottom is no substitute, which Illinois Extension and North Carolina State both state plainly.

Dry indoor air is the other winter thing

Radiators and vents pull moisture out of the air, and plants notice it before you do. Illinois Extension suggests keeping indoor herbs at 70 degrees or below and grouping a few pots together. The Missouri Botanical Garden adds the same temperature ceiling, suggests keeping plants clear of hot drafts, and points at humidity around 50 percent as comfortable.

A pebble tray is the low effort fix. Fill a shallow dish with water and stones, then sit the pot on the stones above the water line. And if a pot sits right above a radiator, move it a foot to the side. The small amount of light you give up is a good trade.

How long until something shows up?

This is the question behind most of the waiting. Here are the real numbers from our own kit packaging. Keep them next to the pot and the whole thing gets easier.

What you planted Time to sprout Kit
Basil 7 to 14 days Organic culinary herb
Chives 7 to 14 days Organic culinary herb
Coleus 7 to 21 days Coleus holiday pail
Cilantro 14 to 21 days Organic culinary herb
Mint 14 to 21 days Peppermint mini pots
Chamomile 14 to 21 days Zen garden
Rosemary 14 to 30 days Rosemary holiday pail
Alpine strawberry 4 to 6 weeks Strawberry windowsill
Lavender 4 to 8 weeks Zen garden

Two things to take from that table. Basil, chives and coleus are the quick ones, so those are the kits for someone who wants to see a result. Lavender and alpine strawberry sit at the patient end, where four to eight weeks of plain growing medium is exactly what the packet describes.

Rosemary at 14 to 30 days lines up with what UMass reports, which is 12 to 28 days or more, and uneven. Uneven is the useful word there. Rosemary comes up a few seeds at a time across several weeks, so sow the whole packet and let the strongest seedlings carry on.

Alpine strawberry seedlings growing indoors on a windowsill planter
Alpine strawberry takes four to six weeks, so the packet and the pot are both telling the truth in week two.

Which kits are easiest to win with in December

If you are giving or receiving one over the holidays, the quick sprouters make the nicest first experience. All of these live on a windowsill, so none of them need outdoor space.

The organic culinary herb kit is the easy pick, because basil and chives are up inside two weeks. The coleus holiday pail is the prettiest quick result, and coleus is a houseplant by nature, so it stays indoors year round.

The peppermint mini pots sit in the middle at 14 to 21 days, and mint is forgiving once it starts. One note from our kit: keep mint in a pot, since it spreads enthusiastically once it reaches open ground.

The slower kits are still lovely gifts for the right person. The rosemary holiday pail and the zen garden kit suit someone who likes a slow project, and both are windowsill plants.

One to choose deliberately. A spruce kit starts on a sill, and a spruce is a tree. It eventually wants a bigger pot or a spot outside. If the person you are giving it to has no outdoor space, the coleus or the herb kits are the better match. We wrote a full piece on the spruce timeline if you want the long view first.

Everything is in the holiday grow kits collection if you would rather browse.

Contents of a holiday grow kit: pail, growing medium pellets and seed packet
What is in the box. The pellet expands with water into the growing medium.

What to do when February arrives

Two jobs, both small.

Move seedlings up when they are ready. Every extension source points to the same signal, which is the first true leaves, meaning the set that follows the two little starter leaves. The University of Minnesota suggests a pot an inch or two wider. Lift the seedling by a leaf, which is the one handling habit worth keeping, because the stem is the fragile part.

Then enjoy the light coming back. By late February the days are noticeably longer and everything on the sill picks up speed. Plants that spent January looking stretched start filling out, with no change in what you are doing.

If anything on your sill is headed outdoors later, late winter is when to read up on hardening off. That means a week or two of gradual outdoor exposure before it moves out. Iowa State suggests 7 to 10 days, starting somewhere shady. Herbs can also simply stay on the sill, which is what most people do.

The short version

Your warm room sprouts seeds nicely, and that part needs nothing from you. Give the seedlings the brightest window you own and turn the pot every few days. Keep them clear of the radiator. Check the surface daily and water when it is dry. Add a cheap lamp on a timer if you want a stockier plant. Then find your seed in the sprout table, trust the number, and let February do the rest.

Keep reading: Grow Kits, Explained: What's in the Box · Cactus Grow Kits: What Really Happens in the First Year · Apothecary Garden Kits: From Seed to Tea Jar · Summer is Winding Down. Your Herb Garden Doesn't Have To

Sources
Back to The Blog