Seed Starting Schedule: When to Sow Vegetables Indoors

In short: Leeks and onions need the longest head start indoors, sweet potatoes the shortest. The dates are Minnesota's; the weeks are what travel to other gardens, counted back from the day you plant outside.

What the table shows

The University of Minnesota Extension keeps a table of when to sow seeds indoors and how long the seedlings stay inside. This page keeps its vegetable rows and leaves out the flowers. Each row pairs a start month with a number of weeks indoors. The rows run from early February, when leeks and onions go in, to a closing row in early to mid May that names no crop and says only to harden off all plants. In between are 6 start dates for vegetables.

The month column belongs to Minnesota. The same page says that tomato, pepper and eggplant are usually started there in early spring, and its remarks on sunlight are about a Minnesota spring. Read the months as one northern state's calendar. The weeks column is the part that travels. The weeks are the part to carry over to other gardens, and the Georgia and North Carolina figures further down are close to Minnesota's. The date a seedling can go outdoors depends on your frost dates.

Reading the weeks

Leeks and onions get the longest head start, 14 to 15 weeks from an early February sowing. Celery follows at 12 to 13 weeks. Broccoli, Brussels sprouts, cabbage, cauliflower and head lettuce share an early March start and 10 to 11 weeks indoors. Eggplant, okra and peppers go in during mid March for 9 weeks. Tomatoes wait until early April and spend 5 to 6 weeks indoors. Sweet potatoes, started in mid April, need only 3 to 4 weeks.

The last row is the one people skip. It says to harden off all plants, and it gives that step 1 to 2 weeks. Seedlings that have spent their whole lives indoors need that time outside before planting, and the hardening off checklist lays out the steps.

The source adds two details that the table cannot. Onions and leeks are the exception to its advice of one seedling per container, because they can start in one larger flat and be transplanted small. And cabbage and broccoli meant for a fall crop may be started indoors in June or July, which is a second, later start for the same crops.

Moving the schedule to your garden

Pick the day you expect to plant outdoors, then count back by the weeks in the row. That is the date to sow. NC State Extension uses the same method in its own planting calendar, advising that you start seedlings 6 to 8 weeks before transplanting them. The counting is simple enough to do on a paper calendar, and this site does not run it for you.

What you cannot read off this table is your planting-out day. Your own frost dates are the other half of that decision, and the frost dates lookup gives them for the weather station nearest you. Tender plants such as tomato and pepper should not go out until frost is past, and your county Extension office can give you the local frost dates.

Three universities, three answers

The sources do not agree to the week, and the gaps are worth seeing. Minnesota gives tomatoes 5 to 6 weeks and peppers 9 weeks. The University of Georgia says tomatoes take 6 weeks to reach transplant size and peppers and eggplants take 8 weeks. NC State gives one range for everything, 6 to 8 weeks. None of them explains the difference, so treat each figure as a window and let the size of transplant you want decide where in it you land.

Worked example: a tomato tray and a pepper tray

Say you plan one tray of each. The pepper row sits at mid March with 9 weeks indoors. The tomato row sits at early April with 5 to 6 weeks. Count forward on a calendar from each start and both trays reach the end of their weeks in May, which is where the table's last row, the hardening-off step, sits. Peppers start earlier than tomatoes and finish at about the same time, because they need more weeks. That is why the pepper tray is sown first.

If your garden is warmer than Minnesota, the whole pair slides earlier, and the gap between the two sowings stays the same.

What the table leaves out

It gives no germination times, so a tray that has not sprouted is a question for the seed packet, which gives the germination time for that variety. If seedlings come up tall and thin, the leggy seedlings fix starts with light. It also covers a limited list of vegetables, and for anything missing, the seed packet and your state Extension service are the next stop.