Step 3 - Seed Starting
Grow Lights vs a Sunny Windowsill
The most common seed-starting question, and the one where the honest answer costs about what two trays of transplants cost.
Janet H. - the hands-on owner behind Janet Media Group.
Published - last updated
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A windowsill will germinate seeds perfectly well. What it will not do is grow a compact, sturdy seedling in late winter, because the light arrives from one side and there is not enough of it. If you are sowing in February or March, buy a light.
| South-facing windowsill | LED strip 3 in above | |
|---|---|---|
| Direction | One side only, so seedlings lean and stretch | Directly overhead |
| Hours | Whatever a short winter day gives | 14 to 16, set by a timer |
| Intensity at the leaf | Low, and cut further by the glass | High, because it is close |
| Consistency | Varies with weather and season | Identical every day |
| Temperature at the glass | Cold at night, hot in direct sun | Stable room temperature |
| Typical result | Pale, stretched, floppy stems | Short, stocky, dark green |
Quick picks
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 |  Top pickBarrina T5 Full-Spectrum LED Grow LightsLinkable LED strips, full spectrum | Stopping leggy seedlings | 9.0 | Check price on Amazon |
| 2 |  Burpee Self-Watering Seed Starting KitCell tray, dome and watering mat in one box | First-time seed starting | 8.4 | Check price on Amazon |
| 3 |  Bootstrap Farmer 1020 Seed TraysHeavy-gauge 1020 trays, reusable for years | Trays that last more than one season | 8.5 | Check price on Amazon |
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Scores are our own editorial judgment, formed from published specifications and independent sources. They are not aggregated customer ratings, and they are not the result of hands-on testing, which we do not currently do. See how we choose.
Why a window fails in late winter specifically
Three things stack up. Day length is short, so total light hours are low. The sun sits at a low angle, so intensity through the glass is well below outdoor levels. And the light is directional, so the seedling invests in stem length reaching toward it rather than in thickness and roots.
Extension guidance identifies insufficient light as the most common cause of leggy seedlings, and a stretched seedling never fully recovers. It goes out into the bed weak and stays behind a later-sown plant that grew properly from the start.
When a windowsill is genuinely fine
- Late spring sowings, when days are long and the sun is high. A window in May is a different proposition from a window in February.
- Germination only, if you move the tray under a light or outdoors as soon as the seeds are up.
- Microgreens and sprouts, which are harvested long before stretching matters.
- A genuinely bright, unobstructed south window in a mild climate, for a small number of tough crops such as brassicas.
Choose a windowsill if
- You are sowing after the spring equinox and the window faces south.
- You are starting a handful of plants rather than trays.
- You can turn the tray daily and accept some leaning.
Choose a grow light if
- You are sowing in January, February or March.
- You want tomatoes, peppers or eggplants, which need the longest head start.
- You are raising more than a tray or two and want them uniform.
- Your last attempt produced pale, floppy seedlings. That is a light problem with a cheap fix.
For specific lights and hanging heights, see the best grow lights for seedlings. For the timing that decides when you need one at all, when to start seeds indoors.
The picks in full
Top pick
Barrina T5 Full-Spectrum LED Grow Lights
Barrina
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The fix for the most common seed-starting failure. A windowsill grows pale, stretched seedlings; a strip light 3 inches above them does not.
A seedling stretches toward light. On a windowsill in February the light comes from one side and there is not enough of it, so the stem elongates, the plant gets pale and floppy, and it never fully recovers. That is the single most common seed-starting failure and it is entirely a light problem.
LED strips fix it because they can sit 2 to 4 inches above the leaves without cooking them. Distance is what matters more than wattage: the same light at 18 inches does very little.
Run them about 14 to 16 hours a day on a timer and raise them as the seedlings grow. Linkable strips mean a whole shelving rack runs from one outlet.
What works
- Directly fixes stretched, leggy seedlings
- Linkable, so one outlet runs a whole shelf
- Very low heat, so it can sit close to the leaves
- Cheap to run
What does not
- Needs to be within a few inches of the seedlings to work
- Height must be adjusted as plants grow
- White light is unflattering in a living space
Skip it if: you have a genuinely bright greenhouse and are sowing in season. Then you are buying light you already have.
| Type | Linkable LED strip lights |
|---|---|
| Spectrum | Full spectrum, commonly 5000K white |
| Lengths | 1 ft, 2 ft and 4 ft strips |
| Mounting | Clips, hanging kit or double-sided tape |
| Linking | Strips daisy-chain from one outlet |
First-time seed starting
Burpee Self-Watering Seed Starting Kit
Burpee
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Everything in one box with a capillary mat underneath, which removes the single most common beginner failure: uneven watering.
Seeds fail for two reasons in a beginner's first tray: they dried out, or they were drowned. A capillary mat drawing water from a reservoir underneath removes both, because the medium takes what it needs and no more.
The dome is the other useful piece. It holds humidity during germination, which matters most for small seeds sown shallowly.
Take the dome off as soon as the first seedlings are up. Left on, it holds the still, damp air that damping-off fungus needs, and a tray can collapse overnight.
What works
- Capillary watering keeps moisture even without daily attention
- Humidity dome improves germination rates
- Nothing else to buy to get started
- Reusable for several seasons
What does not
- Cells are small, so seedlings need potting on quickly
- Kit price is high relative to buying components
- Dome must come off promptly once seeds germinate
Skip it if: you already have trays. Refill pellets and a dome cost a fraction of a new kit.
| Type | Self-watering seed starting kit |
|---|---|
| Cells | Sold in several counts, commonly 36 and 72 |
| Watering | Capillary mat and reservoir |
| Included | Tray, cells, dome, growing medium |
Trays that last more than one season
Bootstrap Farmer 1020 Seed Trays
Bootstrap Farmer
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Thick enough to pick up full without folding, which is the entire complaint about cheap trays and the reason these cost more.
Anyone who has carried a cheap 1020 tray full of wet compost knows the failure mode: it folds in the middle and the seedlings go on the floor. Heavy-gauge trays do not do that.
The 1020 name is a standard footprint, roughly 10 by 20 inches, and it is worth sticking to. Every humidity dome, heat mat, cell insert and shelf is built around it.
Buy a couple of solid, undrained trays alongside the drained ones. A solid tray underneath lets you water from below, which is gentler on small seedlings than watering from above and keeps the leaves dry.
What works
- Can be lifted full of wet medium without collapsing
- Lasts many seasons rather than one
- Standard 1020 footprint fits every dome and mat
- Solid trays double as reservoirs for bottom watering
What does not
- Several times the price of disposable trays
- Only worth it if you actually reuse them
- Heavier to store in quantity
Skip it if: you start one tray a year. The economics only work once you are reusing them season after season.
| Type | 1020 standard seedling trays |
|---|---|
| Gauge | Heavy-duty, substantially thicker than standard |
| Drainage | Drain-hole and solid versions sold |
| Compatibility | Fits standard domes, mats and inserts |
Common questions
Can you start seeds on a windowsill without a grow light?
Seeds will germinate fine. The problem is what happens next: in late winter a window gives directional, low-intensity light for a short day, so seedlings stretch and stay weak. After the spring equinox, on a bright south-facing window, a windowsill becomes genuinely workable.
Why are my windowsill seedlings falling over?
They are leggy -- the stem elongated reaching for light that was too weak and came from one side. Turning the tray daily helps slightly and does not fix it. An LED strip 2 to 4 inches above the leaves for 14 to 16 hours a day does.
Is a grow light worth it for just a few seedlings?
A basic linkable LED strip costs roughly what a few trays of transplants cost, and it lasts for years. If you intend to start seeds more than once it pays for itself quickly, and it is the difference between seedlings that transplant well and seedlings that never catch up.
Does window glass block the light plants need?
Ordinary glass cuts intensity and blocks most ultraviolet, though plants do not depend on UV for growth. The bigger issue in winter is simply how little light there is to begin with, and the fact that all of it arrives from one direction.
Sources
Factual claims on this page are backed by the published sources below, and product specifications are the manufacturers’ own. Where a figure is not published, we say so rather than estimating it.