When Do I Plant?
Remember back in elementary and high school when most of us complained to our teachers or parents “I’ll never use math in real life! ”Well, that day has come. Technically, when you were figuring out how many plants you needed for your space, you were using an algebraic equation – be sure to tell your younger self that! Or, for those of us with kids, tell our kids :)
When you calculate the date that your plants need to go into the ground in order to give you a harvest by a specific date you’re using simple math: take the desired harvest date and work backwards using the number of days to maturity to give you the transplanting date.
Here’s what that simple equation looks like:
Harvest date – DTM = transplant/field date
DTM. You'll often see "DTM" or "GDD" listed on seed packets and sometimes on plant starts. DTM stands for Days to Maturity. GDD stands for Growing Degree Days. Both of these abbreviations/terms give you an indication of how long your crop needs to be in the ground before it is ready to harvest. Of course, these numbers are set under ideal conditions! Here in the Pacific Northwest I have learned that some crops (ahem, carrots and beets) take a lot longer than what the seed packets state.
Let’s revisit our 5 bedft of snapdragons. Snapdragons don't mind frost. I usually start my seeds in late January or early February and transplant them into the garden in March or April, depending on how quickly I can get my soil ready! All of that is to say that I don't have to worry about frost when I determine when I want my snapdragons to bloom.
So, let's choose July 5th for my target bloom date for my 5' of snapdragons. When should I transplant the starts into my bed?
I have a working or blank excel sheet open (you can use the one below) and plug in my target date of 7/5/2021. Then in the next cell, I enter the DTM for my snapdragons - which is a range of 110-120 days for this variety. I'll make it a multiple of 7 (so that my date falls on a Monday) and round up at the end of my DTM range (120) just to be sure that my crop is ready on time. That gives me 126 days. Subtract 126 days from 7/5 and I need to transplant my snapdragons on March 1st (3/1) to have them ready to bloom on July 5th.
If you’re buying starts, then you need to make sure that you have them available to you on March 1st. If you’re starting your own seeds, how do you know when to start them to have them big enough to transplant on March 1st?
Just like each crop has a specific DTM, each crop also has a range of time (usually stated in weeks or days) to germinate and grow before it is big enough to set out in the garden or field. Some crops are direct seeded meaning that you plant the seed directly into the ground. Others grow best from transplants. Sometimes this is also a function of where you live – whether your last frost is too late in the season for crops to adequately grow and produce before your first frost comes if you plant the seeds directly in the ground. And sometimes you have a garden like mine where the slugs and critters (along with cats, squirrels and birds) defeat just about all of your direct seeded attempts! In these instances, growing your seeds in a protected environment and planting them into the ground as transplants/starts gives you the best advantage.
Snapdragons fall into that category, mainly because their seeds are so, so, so tiny! Continuing our example from above and using information on the seed packet or from Harris Seeds handy chart (https://cdn.shopify.com/s/files/1/1537/5553/files/CutFlowerQuickfactsGrowingGuide.pdf). I know that snapdragons take 6 weeks to grow to transplanting size. Let’s plug that information into a formula so we know when to sow our seeds inside!
Field date – greenhouse time = seeding date
3/1/2021 – (6 weeks or 42 days)= seeding date
1/18/2021 is my seeding date.
I repeat this process for each garden bed and use a spreadsheet to keep all the information in one place. Feel free to use the excel sheet below, which is my starting sheet for flowers :)
I used the above sheet to plan a u-pick flower farm and also a similar one to plan an entire 16-acre farm one season. Hopefully it's a little helpful for you in your situation!
A note about field dates...
In the working example above I used July 5th as my target date. In western Washington that is a "safe" date to be assured that there will be blooms. You'll want to know your average last frost date and average first frost date for your area before you pick any harvest dates for your crops. Sometimes it works best to start with your transplant date instead of your harvest date, especially with tender annuals like tomatoes, squash, nasturtiums and marigolds. You can then subtract your greenhouse dates to find your seeding date and add DTM days to find your harvest date.
If you're planning on succession planting (planting multiple crops through out the season so you have a continuous supply of said item) then picking harvest dates a few weeks to a month apart works well, keeping your frost parameters in mind.
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