Seed to Harvest Countdown
Not sure when your hydroponic plants will be ready? This free seed to harvest countdown calculator tells you exactly what growth stage your crop is in right now, when to expect your first harvest, and what signs to look for when it is ready to pick.
Enter your crop, whether you started from seed or transplant, and your planting date. The calculator tracks your grow in real time and, in fact, shows each stage with the days it covers, plus the pH and EC targets to hold along the way.
Step 1 of 3: Choose your crop
What are you growing?
Your harvest countdown
From seed vs from transplant
Growth Stage Timeline
Harvest Signs
How to use this seed to harvest countdown calculator
- Choose your crop from 39 hydroponic crops. Use the category tabs, meanwhile, to filter by leafy greens, herbs, fruiting vegetables, or specialty crops.
- Select your starting point. From seed counts from the day the seed enters the medium, since that includes germination. From transplant, though, counts from the day the seedling enters your system. Your results show both windows side by side, so you can see exactly what the difference costs.
- Enter your planting date, meaning the day seeds went into the medium or the day you transplanted. A past date works fine, though, if your grow is already underway.
- Read your countdown and see the current stage, the harvest window, days remaining, the EC to run right now, and the signs to look for when it is time to pick.
Common questions about hydroponic grow times
What is the fastest crop to grow hydroponically?
Microgreens and wheatgrass are the fastest overall, reaching harvest in 7 to 14 days from seed. For full-size crops, baby bok choy is quickest at 25 to 35 days, then lettuce at 4 to 5 weeks for first leaves, arugula at 30 to 40 days, and basil at 5 to 6 weeks. Green onions regrown from grocery root ends beat all of them at 2 to 3 weeks, though from seed the same crop takes 6 to 10 weeks. Dwarf peppers are, by contrast, the slowest at 10 to 14 weeks.
How long does hydroponic lettuce take from seed to harvest?
Hydroponic lettuce typically takes 4 to 5 weeks, or 28 to 35 days, from seed to first harvest. From transplant, however, it is roughly 16 to 23 days. Steady light on a 14-hour schedule, water held at 65 to 75°F, and EC 1.0 to 1.4 all push growth toward the faster end of that window. A plant sitting in a window rather than under a light will run behind, sometimes by a week or more.
How long do hydroponic cherry tomatoes take?
Cherry tomatoes take about 12 to 16 weeks from seed to first ripe fruit, or, from transplant, roughly 8 to 12 weeks. Strong light of 400 to 600 PPFD and daily hand-pollination are both required for indoor fruit, since skipping either means flowers that drop without setting. Full-size tomato varieties take considerably longer and are, therefore, a poor fit for an apartment.
What does cut-and-come-again mean?
Cut-and-come-again means you harvest outer leaves or stems repeatedly from the same plant rather than pulling the whole thing out. Lettuce, arugula, basil, mint, chives, parsley, and cilantro all regrow after cutting, so a second harvest is often possible. Always cut above a leaf node and leave at least 4 to 5 leaves on the plant, since it needs enough leaf area left to power the regrowth.
Why is my plant taking longer than the countdown says?
Insufficient light is the most common reason, followed by water temperature outside 65 to 75°F, EC too low, or pH outside 5.5 to 6.5 causing lockout. Check pH first, because out-of-range pH produces exactly the same slow pale growth as underfeeding even when your EC reads correctly, and people usually respond by adding more nutrient and making it worse. These windows also assume a steady 14-hour photoperiod.
Do I need rockwool or rapid rooter plugs to germinate?
You do not need either for simple Kratky lettuce, since you can germinate directly in the Kratky lid with a small amount of growing medium. For seeds that need consistent moisture, such as basil, tomatoes, and peppers, rockwool cubes at $9.99 for 100 plugs or rapid rooter plugs at $18.99 for 50 inside a humidity dome give much better germination rates. Pre-soak rockwool at pH 5.5, deliberately below the normal range, because the cube is alkaline and pulls the number up as it absorbs.
Should I use a humidity dome for hydroponic germination?
Yes for most crops, especially in dry rooms. A humidity dome keeps moisture around the seeds during the critical first 3 to 7 days. The AC Infinity dome at $74.99, however, includes a built-in LED for the germination phase. Once seeds sprout and you see root tips, take the dome off, since damping off is stem rot at the base and it is what kills most indoor seedlings.
When should I start measuring EC and pH?
Start checking pH from day one, since it affects germination. Target 5.5 to 6.5 for almost every crop. A few crops sit higher, however: watercress at 6.5 to 7.0, while bok choy, wheatgrass and nasturtiums (6.0 to 7.0) tolerate a higher range. Hold EC at the 1.0 seedling floor until the first true leaves appear, then work up to the crop’s mature range. A few crops start elsewhere: microgreens (0.5 to 1.0), wheatgrass (0.8 to 1.2) and nasturtiums (0.8 to 1.0) start lower, and dwarf cucumbers can start a touch higher, up to 1.5. The calculator shows each crop its own starting EC. A basic pH and EC meter set, though, starts at $14.99.