Calculating When to Plant Seeds


IT HAS PROBABLY BEEN a year since you last figured out when to start sowing your vegetable seeds and now you can’t quite remember exactly when to start. You might be thinking: do I start tomatoes, eggplant or scallions at the end of February, or is it too soon? One thing’s for sure, you had to re-pot the tomato plants three times last year because you started too soon. If you’re like me, you have quite a few varieties to consider, and it can get confusing.

The good news is there’s no need to strain your brain trying to calculate planting dates. There are many online calculators that will do the work for you. These handy Websites let you enter the average last frost date in the spring and spit out dates for planting outdoors or starting seeds indoors for each of your plants.

Some sites even figure out the last frost date from your zip code. If you’re in Canada, you may want to check out number 11 on the list. It accepts Canadian postal codes.

So check out these 11 calculators to see which one you like best.

  1. Organic Science’s Vegetable and Herb Planting Planner –This may be the easiest calculator to use. It uses information from PlantMaps to help you determine your expected last frost date and provides planting dates for both spring and fall.
  2. Burpee Growing Calculator – This is probably the most well known calculator on the list. Burpee provides a number of other online tools for the backyard gardener including hardiness zone information and a gardener question and answer database.
  3. When to Plant Seeds

    Planting date calculators take the effort out of
    calculating when to plant seeds.

  4. Skippy’s Vegetable Garden Planting Calendar – Skippy’s master introduced me to planting calendars, and I wrote about it in this article. For those of you who might be wondering, Skippy is a dog and his master writes the blog called Skippy’s Vegetable Garden (from Skippy’s point of view).
  5. KGI Garden Planning – Much more than a planting date calculator, this handy tool is a complete garden planning system. It’s the only site on the list that is NOT free, and it’s actually provided by GrowVeg.com. I wrote about an earlier version of this software in this article.
  6. Johnny’s Seeds Calculator – An easy to use calculator that focuses on when to start seeds indoors and when to transplant seedlings.
  7. Weekend Gardener Seed Starting Planner – The nice thing about this calculator is it lets you see the results as either a table or a list. Keep in mind, however, that the Weekend Gardener only shows you what needs to be done this week and not the entire plan. You have to keep coming back week after week to make sure you know what to do.
  8. GeeWhyOh Calculator – Apparently, GeeWhyOh stands for “grow your own.” The name is colorful and, as you might expect, this calculator provides dates for succession planting in a colorful, table format. Plus, I just like saying the name!

  9. GrowOrganic Fall Calculator – This free calculator is brought to you by Peaceful Valley, a farm and garden supply company. What’s unique about it is you can buy your seeds right from the calculator’s list of plants. It also lets you include row covers in your calculation, which is kind of nice.
  10. Old Farmer’s Almanac Calculator – This one is unique because it gives you the moon-favorable dates in addition to the typical dates provided by other calculators. So I guess this is the one you want if you’re into bio-dynamic agriculture.
  11. Baker Creek Garden Planting Calendar – This calculator is brought to you by Jere Gettle’s company. Gettle is an heirloom seed expert and was one of the first to encourage Americans to grow unusual varieties in their backyard. I wrote about his book in this article.
  12. All Things Plants Calculator – If you’re in Canada, this might be the one for you because you can enter cities outside of the U.S. or even Canadian postal codes and it will still work.

All of these sites can take a guess at the best time to plant your vegetables, but for planting outside, the best possible way to judge is with a soil thermometer. This article will provide more info on soil temperature, thermometers and planting seedlings.

Have you used any of these planting date calculators? Which one do you like best? Is there another one out there that you like better? Let us know by commenting below.

Related posts you might enjoy:

1. Soil Blocks Versus Paper Pots
2. Five Tips for Starting Vegetable Seedlings Indoors More Cheaply
3. Top Five Vegetable Gardening Books

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One Response to “Calculating When to Plant Seeds”

  1. Rosemary
    March 15, 2013 at 4:36 pm #

    Hi Bill,

    Enjoy your blog as always. I was pleased to read your blog about what to do when you run out of room under the grow lights that gives several ideas, one of which I was already considering. I plan to put down clear plastic sheeting to warm the soil 3 weeks ahead of time. Then build a hoop house tunnel as in your blog, and also set them out in Wall O Waters. I live in zone 5, and read somewhere, maybe on your blogs, that by using all of that you can change your growing zone by 2 zones.

    Now for the subject of this post. I want tomatoes early, so I planned to start them early, thinking they will be closer to their generative stage at planting. How early? My last frost date is May 15th. But I want them in the ground a whole month sooner, April 15th. I also wanted them to be large, stocky plants close to being ready to start producing. So, I started my seeds on January 26th. That date was chosen for getting plants at least 8 weeks old, but I also wanted to try planting by the moon, so I had to back it up a couple more weeks.

    My seedlings this year are the best I’ve ever seen. Wish I could show you pics. Most were slow to sprout though, over 3 weeks total. But man, as soon as they started to get first true leaves, they stayed nice and short and grew big leaves with 3 to 5 leaflets. They are now 7 weeks old, with as many as 7 leaflets, and 6 to 10 inches tall. The leaf canopies measure 14 to 19 inches across on the bigger plants. They look like plants that have already been in the garden a month. How did I achieve this, I’m still asking myself. I wanted short stocky plants like the greenhouses sell. So I searched the net for more facts on how to accomplish that.

    I’ve made a lot of changes in my seedling care and environment. A lot of the info I gleaned from a very informative webpage at: http://urbangardenmagazine.com/2010/08/plant-stress/.
    It’s all information plant on needs, and steering them the way you want by applying minor stresses to the plants. I now incorporate tightly controlled temp, humidity, lighting and watering. Also, I have started to air prune the roots by making my own air pruning pots with wire baskets and burlap lining. This is their second potting up into the air pots, and after only 5 days, roots are emerging from the burlap.

    I’m hoping to get them into the garage in 2 weeks to start hardening off. But that too will be a tightly controlled temp, light, water and humidity setup. Employing the the hoop houses, WOW’s, and plastic to warm the soil, I now need to make the right determination for planting them out in warm enough soil temps. I have doubles of each variety for backups, in case the first planting doesn’t make it. LOL

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