I cut my first small bowl of Black Seed Simpson baby leaves from the raised bed by the back patio just four weeks after I dropped the seeds in. The leaves were soft and pale green, no bigger than my thumb. That early snack is the quick end of the lettuce growing time scale, which runs from about 40 to 80 days for most types you grow to full size. So the honest answer is that it depends on what you plant and how big you let it get before you cut.
The type you plant sets the clock more than anything else. The days to harvest lettuce depends on whether the plant just grows loose leaves or has to pack a tight head. Loose leaf types win the speed race every time. A head type needs weeks of extra growth to build that dense ball you see in the store. So your choice at the seed rack decides most of your wait before you ever water the bed.
Leaf lettuce matures fast because the plant puts all its work into the leaves. There is no head to form, so you can start picking outer leaves as soon as they reach a few inches. Crisphead and iceberg take the longest of all. The plant has to grow a full rosette first, then wrap those leaves tight into a head, and that takes real time. Cool weather helps a head firm up, so a warm spell can stall it for days and stretch the wait even more.
Weather and soil shift the lettuce growing time too. I planted the same Black Seed Simpson seeds in late June one year. They bolted to seed before they ever filled out. My March sowing gave me weeks of leaves instead. Cool spring and fall days near 60°F (16°C) push the fastest, cleanest growth. Heat above 80°F (27°C) makes the plant turn bitter and shoot up a stalk. Good loose soil and steady water keep the plant on its quickest track. Skip both of those and even a fast type drags.
Here is how the main types break down based on extension days-to-harvest guidance. Use these as a starting point and trust your eyes once the leaves look big enough to eat.
You can shave weeks off the wait with a simple trick. Harvest young instead of waiting for a full plant. Baby leaves are ready at about 30 days, and they taste sweet and mild at that size. You do not need to let the plant reach its final stage to start eating from it.
The cut-and-come-again method keeps food on your plate without a long gap. You snip the outer leaves an inch above the crown and leave the center to keep growing. The plant pushes out fresh leaves, and you cut again in a week or two. One looseleaf plant can feed you for over a month this way.
For a steady supply, sow a few seeds every two weeks instead of all at once. This staggers your harvest so you never face a giant pile one week and nothing the next. Pair this with fast growing lettuce like looseleaf or oakleaf and you can pick a fresh handful most weeks of the cool season. Start cutting at the baby stage, keep the crown alive, and your wait shrinks to almost nothing.
Read the full article: Lettuce Growing: A Complete Beginner Guide
