I remember the first time I bought seeds for my garden. They were tomatoes, and the packet read “75 days to maturity.”
So imagine my confusion when the first tomatoes weren’t ready for harvest until the end of June — and this was in a Southern California garden that received ample warmth and sunshine.
It had me looking more closely at other dates of maturity on my seed packets: 80 days for melons, 65 days for cucumbers, 90 days for sweet peppers, 100 days for winter squash.
Sometimes the numbers were off by several weeks, and sometimes they were right on point (give or take a few days).
Why the discrepancies? And why did it seem like most major seed companies printed the “wrong” figures on their packets?
There is no simple answer to the mystery that is “days to maturity” or “days to harvest,” common terms that are used interchangeably in the gardening world.
If you’ve been puzzled by this very thing, here’s what you need to know about those numbers.
First, what does maturity mean?
Plant maturity is a term used with annual flowers and vegetables to indicate when the plants flower or set fruit. When it comes to vegetables, however, maturity is not so well defined.
It is generally accepted that maturity is the point in which you can start picking vegetables, whether they’re ripened fruits (like tomatoes and eggplants), fully-formed but still tightly-closed flower buds (like broccoli and artichokes), or full-sized roots (like beets and radishes).
It’s when beans and peas are at their optimal size, flavor, and texture for eating.
It’s also the point in which leafy greens (like bok choy and cabbage) are full grown and have formed a head or rosette.
However, keep in mind that many vegetables can be picked at various stages, so maturity, in these cases, can span a range of up to three months depending on when you consider the crop to be ready for harvest.
You can harvest tender baby carrots at 3 inches long, or wait until they’re 8 inches long.
Palm-sized zucchini can be harvested with their blossoms still attached, or anywhere from 6 inches to 12 inches long (or even larger).
Some people like to pick baby leaves off lettuce as they grow, while others wait for the lettuce to form heads before picking the whole plant.
When do you start counting the days?
This is where things start getting tricky.
Some seed catalogs and seed packets are self-explanatory and will list days to maturity from seed, or days to maturity from transplant.
Many others, however, list only the days, which leaves you to wonder whether you start counting from the date you sowed the seed, the date the seed sprouted, or the date you set the transplant in the garden.
With little other information, one can assume that days to maturity refers to how the seed is started.
For seeds that are usually started indoors first and then planted in the garden, like tomatoes and peppers, time to maturity is measured from the day you transplant the seedlings in the soil to the day you pick the first ripe fruit.
Even then, the timing can vary widely because one person might sow their seeds earlier, when the soil is cooler and day length is shorter, while another person might start their seeds later under more favorable conditions.
And that leads to another important factor that affects days to maturity…
The time it takes from seed (or transplant) to harvest will differ between different growing regions.
Seed packets list only one “days to maturity,” whether they’re sold in zone 6 or zone 9. But the warmer spring weather and longer growing season of zone 9 means that tomatoes will ripen sooner there than they will in zone 6.
Some years, a warm-weather crop may take longer to reach maturity because of unusually cool weather, and a cool-weather crop may stall and bolt before reaching maturity because of unusually warm weather.
These common variations in days to maturity are directly affected by a heat accumulation index called Growing Degree Days (or GDD).
What are Growing Degree Days?
Growing Degree Days are used in agriculture to determine when a crop will reach maturity. Each day’s GDD is calculated by subtracting a base temperature (which varies by plant species) from the daily mean temperature, with negative values recorded as zero.
For the math geeks out there:
GDD = (High Temperature – Low Temperature) / 2 – Base Temperature
The base temperature for a plant is the temperature at which any significant development slows or stops.
Tomatoes, for example, have a base temperature of 50°F. They do not grow at temperatures below 50°F, and they need 1,300 to 1,700 GDD to ripen (depending on cultivar).
Knowing this, you can effectively predict how many days it will take for a tomato plant to mature in your garden, in your climate, during the growing season.
While GDD is primarily used to predict plant development in commodity crops like corn, wheat, and soybeans, it can be computed for any crop using local weather information.
Temperature is just one part of the whole picture, however.
Environmental stressors can also affect days to maturity.
Rain, drought, pests, over-fertilizing, and under-fertilizing all play a role in how quickly a plant reaches maturity.
Combined with the wide range of climate zones in the country, it makes you wonder how useful the “days to maturity” label actually is when there are so many variables involved.
But — and this might be surprising to you — knowing this number can help you select seeds, plan your garden, and be a better gardener.
How to use “days to maturity” to help you be a better gardener.
By knowing how long it roughly takes for a plant to mature, you can use days to maturity on a seed packet as a guide to compare different varieties of the same vegetable you want to grow.
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For example, if you’re trying to maximize your tomato crop yield, you may come across indeterminate varieties like Early Girl (50 days), Sun Gold (57 days), Green Zebra (75 days), and Beefsteak (96 days).
While these values will differ across climate zones, Green Zebras will always be ready for harvest before Beefsteak tomatoes, no matter where you live.
If you have a short growing season, it’s worth looking into early cultivars (Early Girl) or cherry varieties (Sun Gold), as they’ll ripen a full month before larger slicing tomatoes like Beefsteak, giving you a good harvest before frost sets in.
On the other hand, if you know that it takes 120 days for Pink Banana squash to mature, you can pass on that variety and choose a winter squash that’s more likely to succeed in your climate (like Table King acorn squash, an early maturing variety that takes 80 days).
But if you really wanted to try Pink Banana squash (or any long-season vegetable) in a northern climate, you’ll know that you need to start those seeds indoors to give them a jump on the growing season.
Days to maturity will help you determine how soon you need to start seeds, as well as how many succession plantings are possible in your climate before the weather turns too cold or too hot.
Go with varieties that work well in your garden, save those seeds, and grow them again year after year.
Future plants will acclimate to your local conditions over time, allowing you to calculate a more accurate days to maturity for each variety you grow.
A note on “days to maturity” for a vegetable start.
Days to maturity aren’t just listed on seed packets. They’re also found on plant markers that come with vegetable seedlings and starts at the nursery.
I admit, this is a weird one.
Do you start counting from the day you buy the plant or the day the seed was started by the grower?
It’s hard to get a consensus since nurseries themselves might not even know (unless they started the seeds in their greenhouse and know what stage the plants are at).
But, a generally accepted answer is that the countdown begins from the day you transplant the seedling in your garden (the same way it applies for transplants you started indoors yourself).
When you’re ready to start your seeds:
- How Much to Plant in a Vegetable Garden to Feed a Family
- Seed Starting Supplies on the Cheap: Scouring the Dollar Store
- Seed Starting Containers You Already Have Around the House
- How to Make Recycled Newspaper Pots for Seed Starting
- How to Make Your Own Seed Starting (and Potting) Mix
- The No-Brainer Guide to Starting Seeds Indoors