Reading days to maturity on a seed packet

The packet is counting from one of two events

“Days to maturity” and “days to harvest” are printed as a single number or a range. The number is useless until you know the day it starts. University of Maryland Extension’s planting guide states the rule that seed packets usually follow. For tomatoes, peppers, eggplants, muskmelons, watermelons, broccoli, cabbage, cauliflower, and Brussels sprouts, the number usually means days from transplanting. For other annual vegetables, the number means days from direct seeding, the day the seed goes into the outdoor soil. The same page says harvest dates are set by the average number of days from sowing to maturity, and that variety, a row cover, and full sun versus partial shade all move the actual harvest. The packet number is an average under the conditions the seed company had in mind. It is not a contract.

Maryland’s cabbage page is a worked instance of the same rule. Days to maturity are given as 60 to 90 from transplanting. Spring transplants are started 4 to 6 weeks before setting out. The 60 to 90 does not include those 4 to 6 weeks. Adding them into the packet number double-counts the indoor time. Leaving them out, and then wondering why a cabbage sown indoors is not ready 60 days after sowing, misreads the start event.

Maryland’s indoor-seed page gives the weeks those transplants typically need before they go outside: leafy greens 2 to 4 weeks, cabbage and broccoli and cauliflower 4 to 6, cucumber and squash and melons 3 to 5, tomatoes 5 to 6, pepper and eggplant and onion 8 to 10. Those weeks are a third number. They are not days to maturity. A tomato with “80 days” on the packet and “5 to 6 weeks” in the indoor table is an outdoor transplant that should be sown about five or six weeks before the transplant date, and that should mature about 80 days after that transplant date. The total from sowing to harvest is the sum, and only if both sources apply to the variety in your hand. Texas A&M’s Earth-Kind seedling table, cited in the seed-starting guide, gives tomatoes 5 to 6 weeks and peppers 7 to 8 weeks. Pepper weeks are not the same in the two publications. Use the one you are following. Do not average 7-to-8 with 8-to-10 and call it Maryland.

What Texas A&M’s harvest table refuses to say

Table 9 of the Texas Home Vegetable Gardening Guide is titled as harvest and yield. Tomatoes are 70 to 90 days. Peppers are 60 to 90. Eggplant is 80 to 90. Broccoli is 60 to 80. Cabbage is 60 to 90. Bush snap beans are 45 to 60. Radishes are 25 to 40. Spinach is 40 to 60. Winter squash is 85 to 100. The column is “days to harvest.” The guide does not say whether the count starts at seeding or at transplanting. The crop page keeps that wording. Maryland’s rule describes how packets are usually written, not how Table 9 was built, so the two stay separate. The ranges can still be used. They cannot be used as if the starting event had been declared.

The fall calculator takes the same stance. You type the days. You may type extra days. The extra days default to zero, so a margin appears only when you enter one. The tool subtracts the total from the first 32°F date at the probability you select, 10, 50, or 90 percent. It does not look up Table 9, it does not apply Maryland’s transplant list, and it does not add indoor weeks. If you type 80, you get a date 80 days before the frost date you picked. If your 80 was a transplant-to-harvest figure, that date is a transplant date. If your 80 was a seed-to-harvest figure, that date is a sowing date. The screen cannot see which one you meant.

Two crops, one station, two start events

Austin’s city page uses Camp Mabry, USW00013958. The median first 32°F date there is December 3. The 10% date is November 15. The 90% date is January 1.

Take a radish and Table 9’s 25 to 40 days. Maryland puts radishes with the crops counted from direct seeding, not on the transplant list. Subtracting 25 days from December 3 gives November 8. Subtracting 40 days gives October 24. If you are following Table 9’s range and Maryland’s start event, those are sowing dates aimed at a harvest on the median first 32°F date, with no extra margin. Table 8 also has a fall radish cell, 1 to 8 weeks before the first freeze. From December 3, one week before is November 26 and eight weeks before is October 8. November 8 sits inside that cell. October 24 sits inside it. A 25-day radish aimed at December 3 is a late sowing relative to the cell, and it is still inside the cell. A 25-day radish aimed at the 10% first-freeze date, November 15, would be sown around October 21, also inside the cell. Aiming at January 1, the 90% date, and subtracting only 25 days means the sowing is December 7, which is outside the 1-to-8-week cell and depends on a first freeze that late. The calculator will produce December 7 if you select 90% and type 25. Table 8 will not call it a recommended week. Both results should stay visible long enough for you to notice they disagree.

Take a tomato and a packet that says 80 days, read with Maryland’s rule as days from transplanting. Eighty days before December 3 is September 14. That is a transplant date, not a sowing date. Maryland’s indoor table then asks for another 5 to 6 weeks, which puts sowing in the first half of August: six weeks before September 14 is August 3, and five weeks before is August 10. Table 8’s fall tomato cell is 12 to 14 weeks before the first freeze, which from December 3 is August 27 through September 10. September 14 is four days after that cell closes. An 80-day tomato, transplanted on the day Table 8’s window ends, September 10, would be aimed at about November 29, four days before the median first freeze, if the 80 days hold. The packet’s 70-day end of a typical range would finish earlier. Table 9’s own tomato range is 70 to 90 and still does not name the start event. If the 80 you typed was actually seed-to-harvest, September 14 is a sowing date and the transplant reading above is the wrong story. The arithmetic did not decide. You decide before you type, and you write the start event on the label.

Bergstrom’s median first 32°F date is November 16, not December 3. The same 80 transplant days before November 16 land on August 28. The city page does not use Bergstrom. Running the calculator on the city page and then checking the work against an airport you remember is how a correct subtraction gets compared with the wrong anchor. Read the station name on the page before you trust a date you computed from memory.

Extra days, shade, and the things that move the harvest

Maryland says a row cover and a shift from full sun to partial shade change harvest time. It does not give the number of days for either. The extra-days box is where you put a margin you are willing to name. Ten extra days on an 80-day tomato is a 90-day subtraction. From Camp Mabry’s December 3 median, that is September 4, which falls inside Table 8’s August 27 to September 10 window. You have bought the margin by planting earlier, not by editing the packet. Zero is the starting value, so a margin appears only when you enter one.

Variety is the other move Maryland names. Table 9’s ranges are already a variety span: a 70-day tomato and a 90-day tomato are three weeks apart if both numbers start on the same kind of day. West Virginia’s succession examples, in the succession guide, use that span on purpose by sowing an early and a late variety together. Using the long end of the range for a fall deadline is the conservative reading of an unspecified variety. Using the short end is a bet that you have the fast one. The bet should be on the packet in your hand, not on the middle of Table 9.

Days to maturity are not growing-season length. NCEI’s growing-season length is the number of days the freeze-free season meets or exceeds at a stated probability. Camp Mabry’s median 32°F season length is 291 days. An 80-day tomato does not “fit 291 divided by 80” times, because the season length is not a string of identical 80-day slots, the tomato cannot use the cold ends of that season, and the 291 days are not measured from transplanting. The season length answers “how long is the freeze-free period.” The packet answers “how long after this start event.” Dividing one by the other is not a planting plan.

A way to read the packet before you use the calculator

1. Find the number. If it is a range, write both ends. 2. Decide the start event. If the crop is on Maryland’s transplant list and you are following Maryland, the start is transplanting. If it is any other annual and you are following that page, the start is outdoor sowing. If you are looking at AgriLife Table 9, leave the start event blank unless another sentence in a guide you trust fills it in. 3. If the start is transplanting, subtract the packet days from the frost date to get a transplant date, then subtract the indoor weeks from that date to get a sowing date. Keep the two subtractions in order. 4. Compare the result with the cited outdoor window. If the transplant date falls outside the window, the packet and the extension disagree for this station. Believe the window if you came for the extension’s planting date, and believe the packet only with your eyes open. 5. Type the same number into the calculator only after the start event is settled. Select the probability on purpose. Add extra days only if you want a margin you can explain.

The calculator is a calendar. The packet is a variety claim. The extension window is a third document. They agree when the date you computed sits inside the window and the start event matches the crop. They are not required to agree, and a site that forces them into one unmarked date has thrown away the disagreement you most need to see.

Sources

• University of Maryland Extension, “When to Plant Vegetables,” days-to-maturity paragraph: https://extension.umd.edu/resource/when-plant-vegetables
• University of Maryland Extension, “Growing Cabbage in a Home Garden”: https://extension.umd.edu/resource/growing-cabbage-home-garden
• University of Maryland Extension, “Starting Vegetable Seeds Indoors”: https://extension.umd.edu/resource/starting-vegetable-seeds-indoors
• Joseph Masabni, Texas Home Vegetable Gardening Guide, Table 8 and Table 9: https://agrilifeextension.tamu.edu/library/gardening/texas-home-vegetable-gardening-guide/
• NOAA NCEI stations USW00013958 and USW00013904.