How do I harden off seedlings before transplanting?
Gradually expose indoor seedlings to outdoor conditions over 7–10 days, starting with an hour of shade and building up to full sun and overnight temperatures before planting.
Seedlings grown indoors have never experienced direct sun, wind, or temperature swings. Their cell walls are thin, their waxy cuticle is underdeveloped, and their stems haven't been conditioned by any movement. Put them directly outside in full sun and you'll see bleached, scorched leaves within a few hours — not because the light is too strong in absolute terms, but because the plant was never prepared for it.
The standard approach is a 7–10 day transition. Days 1–2: place plants in a sheltered, shady spot outdoors for 1–2 hours, then bring them back inside. Days 3–4: a shady spot for 3–4 hours. Days 5–6: morning sun (east-facing or dappled light) for several hours. Days 7–8: most of the day in full sun. Days 9–10: leave them out overnight if temperatures will stay above 50°F (for warm-season crops). After this, they're ready to transplant.
Wind is often as stressful as sun. A sheltered spot on days 1–4 matters — plants experience more water stress in wind because leaves lose moisture faster than roots can supply it. Once you're in the final days of hardening, a breezy spot is actually helpful for stem conditioning.
If you get a cold night forecast during the process, bring them in. A frost during hardening is far worse than starting the process over. For warm-season crops like tomatoes and peppers, don't attempt overnight hardening until nighttime temperatures are consistently above 50°F.
- TomatoThe warm-season anchor of the summer garden.
- PepperA tropical perennial grown as an annual — patient, slow, and particular about warmth.
- BasilThe summer companion — to tomatoes, to pasta, and to the gardener with a south-facing window.
- 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.
- Bird DamageBerries pecked or missing, seeds scratched from beds, and seedlings dislodged — birds feeding on ripe fruit, seeds, or soil grubs.
- Imported CabbagewormRagged holes in brassica leaves with pale green caterpillars and green frass nearby.
- Damping OffSeedlings collapse at soil level with a pinched, rotted stem — happens quickly in wet, cool conditions.
- Downy MildewAngular yellow patches on leaf tops with gray-purple fuzzy growth beneath; worse in cool, humid conditions.
- Early BlightDark spots with concentric rings on lower leaves that yellow and drop, working up the plant.
- My transplants look wilted and sad after planting — is this normal?Some wilting and leaf drop in the first few days after transplanting is normal; if a plant is still wilting after a week and well-watered, the roots may have been damaged.
- When should I start seeds indoors?Count backward from your last frost date using the seed packet's weeks-to-transplant number — most tomatoes and peppers go in 6–8 weeks before last frost.
- There's a surprise frost forecast — what should I cover and with what?Cover warm-season transplants and seedlings with row cover fabric or old bedsheets — not clear plastic sheeting directly on leaves — and place covers before sundown to trap daytime heat.