Seed-starting timeline

Two clocks, not one

A seed-starting date is a subtraction. You need an outdoor date, and you need the number of weeks that seedling should spend indoors. The outdoor date on this site comes from a state extension guide when one has been cited. The indoor weeks come from a different sentence, often a different publication, and sometimes only from the seed packet in your hand. Adding those weeks together is the whole method. Inventing the indoor number because a website “usually” says six weeks is how the calendar drifts away from the source.

Texas is the clearest example because Texas A&M AgriLife publishes both pieces, in two different documents. The crop windows follow the outdoor table.

The outdoor clock in the Texas guide

Joseph Masabni’s Texas Home Vegetable Gardening Guide, Table 8, gives spring planting as weeks before or after the frost-free date, and fall planting as weeks before the first freeze date. The guide does not say whether frost-free means the median last 32°F date, the 10% date, or an older average. Spring offsets are applied to the median last 32°F date from the nearest qualified NOAA station, and the crop page says so. The 10% and 90% dates stay on the page so the spread is visible.

At Austin-Bergstrom, USW00013904, the median last 32°F date is March 12. Table 8 places tomatoes 1 to 8 weeks after the frost-free date. One week after March 12 is March 19. Eight weeks after March 12 is May 7. That is the outdoor window this site will test in the “is it inside a published window?” check for a Texas tomato, when Bergstrom is the station in use. A closer station wins if one exists. The arithmetic does not change. Only the anchor date changes.

The same table does not use one offset for every crop. Peppers are also 1 to 8 weeks after. Eggplant is 2 to 6 weeks after, so the early edge is a week later than the tomato’s early edge. Summer squash is 1 to 4 weeks after, a shorter window. Broccoli is 4 to 6 weeks before, which at a March 12 median is January 30 through February 13. The day shift uses the 2024 calendar, so February 29 is included and the subtraction matches the pages. Spinach is 1 to 8 weeks before. Lettuce is written as “6 weeks before or 2 weeks after,” a span that crosses the frost-free date rather than sitting on one side of it. If a countdown treats every crop as “start indoors six weeks before last frost,” it has already thrown Table 8 away.

Cauliflower’s spring cell in that table is “not recommended.” Garlic’s spring cell is “not recommended.” No spring week count is shown for either crop, because the table does not give one.

The indoor clock, from a different AgriLife page

Table 8 is an outdoor timing table. It does not say how many weeks a tomato should sit under lights. AgriLife’s Earth-Kind page, “Timely Tips on Starting Seedlings at Home,” has a separate Table 1, “Planting and growing information for vegetables,” with a column headed “Weeks needed to grow transplants.” The footnote says the number depends on the structure, the heat, and the light. The cells are:

• Cabbage, broccoli, and cauliflower: 5 to 7 weeks.
• Lettuce: 4 to 6 weeks.
• Onions: 8 to 10 weeks.
• Tomatoes: 5 to 6 weeks.
• Peppers: 7 to 8 weeks.
• Eggplant: 7 to 8 weeks.
• Cucumber, squash, muskmelon, and watermelon: 2 to 3 weeks.

The same page says seedlings are ready to transplant when they have the first set of true leaves, and later says transplanting begins when the first true leaves are forming, usually 2 to 3 weeks after sowing. Those two statements are about readiness, not a second calendar. The week counts in the table are the planning numbers. The true-leaf sentence is a check on the plant in the tray. If the tray is ready early, the frost-free date has not moved.

University of Maryland Extension’s indoor-seed page is a useful second source, and it is not identical. Maryland lists leafy greens at 2 to 4 weeks, cabbage, broccoli, and cauliflower at 4 to 6 weeks, cucumber, squash, and melons at 3 to 5 weeks, tomatoes at 5 to 6 weeks, and pepper, eggplant, and onion at 8 to 10 weeks. Tomato weeks match AgriLife’s Earth-Kind table. Pepper and eggplant are a week or two longer at the top end in Maryland’s list. Cucurbit weeks overlap and do not match exactly. The two lists stay separate. Type the weeks from the publication you are following, or from the packet when the packet states weeks before transplant.

One worked tomato, with the weeks kept separate

Stay with Bergstrom and the median, March 12. AgriLife’s outdoor window for tomatoes opens March 19 if you take the early edge, “1 week after.” Earth-Kind says a tomato needs 5 to 6 weeks to reach transplant size. Six weeks before March 19 is February 6. Five weeks before March 19 is February 13. If you instead aim at the late edge of the outdoor window, May 7, six weeks before that is March 26. The result is a range of sowing dates inside a range of setting-out dates.

Do not add a third buffer. The outdoor instruction is already “after” the frost-free date by at least a week. The 10% last-32°F date at Bergstrom is April 2, which means about one year in ten the last 32°F minimum falls on or after April 2. The countdown on this site will anchor to the median last 32°F date or to the first day of the cited outdoor window. It will not anchor to April 2. If you want the indoor weeks counted from that 10% date, subtract them yourself and say that is what you did. Counting six indoor weeks back from March 19 and then sliding another two weeks “for safety” produces a sowing date the two AgriLife pages did not write.

The fall side is a different outdoor clock. Table 8 places tomatoes 12 to 14 weeks before the first freeze date. That offset is applied to the median first 32°F date. At Bergstrom that median is November 16. Fourteen weeks before November 16 is August 10. Twelve weeks before is August 24. Earth-Kind’s 5 to 6 indoor weeks, counted back from August 10, are June 29 through July 6. That is a fall transplant schedule. It is not the spring schedule run backward. The fall timing guide covers the other Texas document, the regional fall chart, which is in calendar dates rather than weeks.

How the countdown is anchored

The seed countdown subtracts the weeks you enter from the median last 32°F date, or from the first day of a cited outdoor window when that window has a start and an end. The Earth-Kind week table and Maryland’s week table stay in this guide. They are not applied to every state, because those weeks belong to the publications that printed them.

A calendar span such as “April 15 to May 30” can anchor the countdown on its first day. A phrase without two endpoints is quoted as written. In a state without a cited outdoor window, the countdown still counts back from the median last 32°F date.

Days to maturity are a third clock. They are discussed in reading days to maturity. AgriLife Table 9 lists tomatoes at 70 to 90 days and does not say whether the count starts at seeding or at transplanting. Maryland says that for tomatoes the packet number usually starts at transplanting. Using 80 days as if it were indoor growing time, or using 6 weeks as if it were days to harvest, crosses those clocks. Keep them in separate columns on a piece of paper if the screen is showing only one of them.

A short sequence that stays inside the sources

1. Read the outdoor window on the crop page and the sentence that says which frost date it was applied to. 2. Pick the edge you mean: the early end of that window, the late end, or the median frost date itself. Write the choice down. 3. Read the weeks-to-transplant from the publication you are using. For a Texas tomato that can be Earth-Kind’s 5 to 6, or Maryland’s 5 to 6, or the packet if it states a number. Do not mix a pepper’s 7 to 8 into a tomato tray. 4. Subtract. Seven days times the weeks, back from the outdoor date you picked. 5. Look at the 10% last-32°F date before you commit the tray to a bed. The subtraction did not consume that risk. It only scheduled the sowing.

Record the sowing date and the date the first true leaves appear. The Earth-Kind page asks for that notebook on purpose. A tomato that is still tiny at week six has not reached the size the table describes.

Sources

• Joseph Masabni, Texas Home Vegetable Gardening Guide, Table 8 and Table 9, Texas A&M AgriLife Extension: https://agrilifeextension.tamu.edu/library/gardening/texas-home-vegetable-gardening-guide/
• Texas A&M AgriLife Earth-Kind, “Timely Tips on Starting Seedlings at Home,” Table 1: https://aggie-horticulture.tamu.edu/earthkind/landscape/starting-seedlings-at-home/
• University of Maryland Extension, “Starting Vegetable Seeds Indoors”: https://extension.umd.edu/resource/starting-vegetable-seeds-indoors
• NOAA NCEI station USW00013904, 1991–2020 annual/seasonal normals, used only as the worked median.