How do I know when to start garden seeds indoors and outside? Find out what to plant when, specific to your area with these following tips. Figuring out when to start garden seeds is an important piece of garden planning.
If you plant too early, plants may not survive. If you plant too late, plants may not grow as well without the ideal growing conditions.
I’ve found a few resources over the years that are helpful to figure out when to start garden seeds so thought I’d share since I hear this question asked a lot!
Figure Out Your Growing Zone
The first step is to figure out your growing zone. I’ve always used the handy Plant Hardiness Zone calculator on the USDA website. This is a great interactive tool that shows a colored growing zone map. Enter your town and state to zero in on the specific growing zone for your home.
This is important because there are zone variations even within the same town. For example, our homestead is in a 5b zone but people in our same community at a higher elevation are in a 5a zone.
This map will also provide average temperature ranges for your growing zone which is important because some species will not survive colder temperatures and some require hotter temperatures to thrive.
Figure Out Your First and Last Frost Date
Once you know your plant hardiness growing zone, the next step is to figure out the average first and last frost date for your area. This is the the average date of the last light frost in Spring and the first light frost in the fall.
If you’re in a colder state like Montana, that first light frost often arrives the end of summer well before fall arrives!
When I first moved to Montana 24 years ago, people told me their rule of thumb was to always plant warm season plants after Memorial Day.
I still hear some folks give that advice to new gardeners but it’s actually not totally accurate for all areas of Montana. It’s a rough estimate to keep in mind but narrowing down data specific to your area is key.
The Old Farmer’s Almanac has a handy Frost Dates calculator on their website. Simply type in your zip code and the calculator will provide the first and last frost dates data for your area. This is an estimate to give you insights into your area but it is not perfect.
Some years we have had snow in June and several unexpected early frosts in August! Us gardeners always have to keep an eye on current weather conditions and forecasts to be prepared.
Determine When to Plant Seeds and Seedlings
Now that you know your growing zone and average first/last frost dates, the next step is to determine the best time to plant your seeds.
Seed packets should have growing information on the back of each packet providing growing information and days to germination.
My favorite resource for determining what seeds to plant when in Montana is a free guide from the Montana State Extension Office website.
I’ve been using this reference guide for years, long before I took the Montana Montana Master Gardener Certification Course a couple years ago. What a helpful tool and it’s free!
What I love about this guide is that the chart provides recommendations for planting dates for seeds or seedlings, frost tolerance, sun requirements and days to maturity.
This is especially helpful when saving our own heirloom seeds since we don’t have the handy information written on the back of our seed envelopes.
A few years ago I printed out this chart and keep a copy in my seed organizing notebook. It is definitely a well loved chart showing it’s age!
Keep a Garden Journal
A few years ago someone suggested I keep a garden journal like these to keep track of what I planted when, document successes and failures so I could learn from my experiences each year. This was such great advice!
I find myself referencing my garden journal when doing my annual garden planning. It also helps me remember what we planted when and where so we can ensure crop rotation in our gardens.
A garden journal is a great place to note when you started seeds for specific plants so you can reference this the following year and make adjustments as needed.
Schneider Peeps also has a really great comprehensive printable Gardening Notebook with over 120 pages to help you with your garden planning.