Why are the first leaves on my seedlings turning yellow?
The first two leaves (cotyledons) yellow and drop naturally once true leaves take over — this is normal unless the yellowing is moving up into newer growth.
Every seedling starts with two seed leaves called cotyledons. These are pre-formed inside the seed and look different from the plant's adult leaves — round and smooth where the true leaves will be lobed or serrated. The cotyledons' job is to fuel early growth by converting stored seed energy, and once the first set of true leaves is photosynthesizing on its own, the cotyledons yellow and fall. This is not a problem. It's the plant doing exactly what it should.
The question to ask is: where is the yellowing? If it's confined to the cotyledons and the true leaves above them are green and growing, you can ignore it. If yellowing is appearing in the true leaves — especially if they're pale between the veins, or yellowing from the bottom of the plant upward — that suggests a real problem. Nitrogen deficiency is the most common cause in seedlings growing in seed-starting mix for more than 4–5 weeks, since most mixes contain little to no fertilizer.
A dilute liquid fertilizer — half the labeled rate of a balanced formula or a fish emulsion — applied every 10–14 days after the first set of true leaves appears can prevent this. Don't fertilize before true leaves appear; the seedling doesn't need it yet and concentrated fertilizer near young roots can cause burn.
Overwatering can also cause pale, yellowing true leaves by excluding oxygen from the root zone. If the mix smells sour or stays wet for more than 3 days between waterings, reduce frequency and improve drainage before reaching for fertilizer.
- TomatoThe warm-season anchor of the summer garden.
- PepperA tropical perennial grown as an annual — patient, slow, and particular about warmth.
- CucumberA thirsty vine that wants warm soil, steady water, and something to climb.
- ZucchiniThe summer squash that turns a garden into a produce stand — if you can keep the vine borers away.
- BasilThe summer companion — to tomatoes, to pasta, and to the gardener with a south-facing window.
- AphidSoft, clustered insects on new growth causing curled leaves and sticky honeydew.
- Bird DamageBerries pecked or missing, seeds scratched from beds, and seedlings dislodged — birds feeding on ripe fruit, seeds, or soil grubs.
- Black RotV-shaped yellow lesions at brassica leaf margins with blackened veins inside — a bacterial disease that moves through the vascular system.
- Brown Marmorated Stink BugSunken, corky dimples on fruit and pods caused by a mottled brown shield bug feeding through the skin.
- Cabbage MaggotBrassica transplants wilting and dying as white maggots tunnel through roots at or below the soil line.
- Why are my seedlings tall, pale, and floppy?Seedlings stretch toward inadequate light — the fix is moving them closer to the light source, not giving them more hours of light.
- Why aren't my seeds germinating?Cold soil is the most common culprit — most vegetable seeds stall below 60°F, and old or improperly stored seed may not be viable at all.
- Why do my transplants look stunted and aren't growing?Cold soil, root-bound roots, or fertilizer burn can all stall a transplant — check soil temperature first before diagnosing anything else.