Seed Starting: Growing Days

Starting plants from seed is not only budget-friendly but also opens up a wide range of plant options and gives a head start to Laramie County's short growing season. Understanding the different growth phases of a plant and their anticipated growing timelines can enhance your gardening success. Seed packets can sometimes be a puzzle with their abbreviated instructions, but don't worry, we're here to help! We are presenting a series of blog articles to demystify the seed starting process. Today's article is "The Truth About Growing Days."

Seed Packets (photo by S. Sauls)

Seed Packets Decoded

Seed packets: small envelopes or bags filled with plant seeds and containing valuable information to ensure successful growth. Here's what you may find on the packet:

• Seed type: the plant variety (e.g., "Heirloom Tomato" or "Patterson Onion")

• Planting instructions: how deep to plant the seed, how far apart the spacing should be from other seeds, special treatments such as cold stratification or scarification, etc.

• Number of days: this typically refers to "Days to Maturity," although some packets may also mention "Days to Germination"

And some information is just missing, as seed providers can make assumptions about a gardener's knowledge. Growing conditions such as light, temperature, water (vegetables aren't drought-tolerant, you know), growing medium, etc., may not be on the packet (we'll explore this topic in another blog in a couple of weeks).

It's easy to think we understand the instructions, but what are they really (or not really) telling us? For instance, "Number of Days" often causes confusion. I admit I initially thought it referred to the total time from planting the seed to gathering the harvest, but in reality, it usually means "Days to Maturity," which is the time from seedling transplant to harvest, excluding the time for a seed to sprout from your growing material (germination) and the "hardening off" period.

Phases of Plant Growth

Understanding plant growth phases and the time it takes from planting a seed to harvesting your crop can greatly enhance your gardening success.  In general, a plant’s growth consists of four stages:

• Germination Stage: This is the period from planting a seed (Day 1) until it starts to sprout (you’ll see tiny shoots emerging from the soil).  The seed packet may identify this time as “Days to germination,” which can vary from days to weeks depending on your seed variety.

• Seedling Stage: During this phase, the tiny plant develops its first “true leaves” and grows stronger.  The first set of leaves that emerge are called cotyledons or seed leaves.  The next set of leaves, which look more plant-like, are the “true leaves.” 

• Hardening Off & Transplanting: This is the time to gradually acclimate your indoor seedlings to outdoor conditions—a process known as “hardening off.”  Seedlings have only known the comforts of a controlled environment, so moving them directly outside without an acclimation period might kill them.  To minimize transplant shock, you’ll typically want to take 7-14 days to gradually increase their exposure to outside elements before they are strong enough to transplant outdoors. 

• Growth Period (Maturity) to Harvest: Once transplanted to their final growing location (garden or larger container), plants enter the maturity phase.  This includes vegetative growth, flowering, and producing fruit. 

Growing conditions significantly affect plant growth. Factors like temperature, sunlight, soil quality, and water availability play crucial roles. If any of our growing conditions fall short, those days won't necessarily count as optimal growing days.

Calculating Total Growth Time

A good calculation for understanding total growing days (seed start to harvest) is:

As an example, let’s consider the growth timeline of a Brandywine Tomato.  The tomato’s seed packet mentions 78 days to maturity and 5-7 days to germination.  But don’t forget, you’ll need to factor in the time needed to grow seedlings indoors.  Typically, a Brandywine Tomato can take about 5-6 weeks (35-42 days) before it is ready for transplant, plus another 10-14 days to harden it off before transplanting.  In total, you’re looking at approximately 141 days from seeding to harvest (7 days to germinate + 42 days indoor growth + 14 days hardening off + 78 days to maturity = 141 days). 

Knowing the results of this calculation may help you decide whether to start your seed early indoors or wait to seed directly outdoors.  If this was lettuce, I would most likely wait and seed it directly outdoors, but this is a tomato with growing days greater than my growing season. I decided to get a 63-day head start with this tomato plant. I prefer to transplant my plants outside no earlier than Memorial Day weekend, therefore I need to start my seed indoors around the last week in March to have them ready for transplant outside (subtract 63 days from May 31st = March 29, 2025). Could you start them earlier than end of March? Absolutely, as long as you have the indoor growing space to up-pot them as they grow.

But wait, I have to keep in mind that growing days are influenced by growing conditions, so I might have less risk if I reconsider this variety altogether and go with a shorter season tomato.

A Word About "Optimal" Growing Days

Let's continue our Brandywine Tomato growing journey. So, I took the plunge and started my seeds indoors late last March to get a head start on the Cheyenne growing season (First Frost Date typically around May 20th; Last Frost Date typically around September 26th; approximately 100-day growing season [2]). The tomato seed packet stated the plant needed 78 days to maturity, which seemed to fit within our 100-day growing season. I transplanted my Brandywine Tomato around Memorial Day to a sunny spot in my garden (over 6+ hours a day) and set it on a timed drip irrigation system. Unfortunately, my tomato plant was slow to grow, and the meek harvest it offered was somewhat tasteless. What happened? Growing conditions, like temperature, can influence growing days.

Here's what I learned… when the seed packet identifies a “Days to Maturity” number, it also means that this is the number of days the tomatoes need to be exposed to optimal conditions. In Cheyenne, weather can be unpredictable, with wind, hail, and temperature fluctuations impacting plant health. Stress from non-ideal conditions can lead to leaf curl, wilting, stunted growth, blossom drop, sunscald on fruit, and poor flavor. In my post-mortem, I learned the ideal growing temperature for Brandywine Tomatoes is between 55˚F and 90˚F. My tomato plant was in full sun, had consistent water, and was protected from hail, yet it still faced challenges. Temperatures between June 1st and Sep 26th were not ideal for the tomato plant. Instead of 78 days of optimal growing days, it experienced approximately 50 optimal growing days… here’s a summary table of my experience with temperatures last year (# days depicted below based on consecutive days, not one-off dips or crests):

Well, no wonder my Brandywines didn’t flourish!  Looking back, I was really pushing it with a variety requiring over 60 days.  Other varieties I grew, like Patio Choice Yellow Cherry Tomatoes and Alpine Tomatoes, did much better and I’m betting it was because they boasted fewer growing days.  Armed with this knowledge, my 2025 tomato seed selection is going to focus on maturity days between 50-60 days.  The University of Wyoming Extension recommends Glacier (55 days) or Early Girl (60 days) and also suggested are the Sun Gold variety (57 days to maturity).

Don’t Be Afraid to Experiment

The 2024 growing season reinforced to me that gardening is all about experimentation, and it’s possible to successfully grow a wide range of seed varieties here.  I may try Brandywine Tomatoes again, making a few adjustments.  I might grow the plant in my unheated greenhouse which tends to stay 5-10 degrees warmer than the outside.  I might be more vigilant about covering my tomato plants on those <55˚F nights.  I might also look for a Brandywine equivalent that has a smaller number of Days to Maturity.  If you’re eager to try a new variety, GO FOR IT!  Just keep realistic expectations in mind. 

Don’t be afraid to experiment!  To help you get started, check out our joint project with the Laramie County Library to provide free seeds to our community.  The Seed Library of Laramie County opens at 10:00 am on March 15, 2025, in the Cottonwood Room at the Laramie County Library.   This year, we are also pleased to extend seed offerings to the Burns Branch Library and Pine Bluffs Branch Library.  Seeds are free and no library card is needed.  For more information, please visit our website (https://www.lcmg.org).

And once you have seeds in-hand, we invite you to our “Let’s Get Growing!” Workshop on March 22, 2025, from 1:00 pm to 3:00 pm, at the Laramie County Community College, Pathfinder Building, Room 305.  (Attendance at Part 1 of this workshop series is not required). Our Master Gardeners will discuss and demonstrate planting instructions, rules-of-thumb, up-potting, growing on, hardening off and transplanting into your garden.  To attend, please register at the event link on our website (https://www.lcmg.org).

Seed packets are handy tools in a gardener’s toolbox.  Understanding the terminology and underlying definitions better equips you to tackle Laramie County’s growing conditions.  We'll be back in a couple of weeks with another seed starting article focusing on growing conditions and their impact on your plants. We can’t wait to see you grow!

Written by Suzanne Sauls, Laramie County Advanced Master Gardener

References:

[1] University of Wyoming Extension Publication B-1340, "Wyoming Vegetable & Fruit Guide," page 24, published November 2021, available for download from https://www.wyoextension.org/agpubs/pubs/B-1340.pdf.

[2] “2025 Frost Dates for Cheyenne, WY,” Farmer’s Almanac, available for viewing online at https://www.almanac.com/gardening/frostdates/WY/Cheyenne