EACH YEAR vegetable gardeners in the northern half of North America need to calculate when to:
- Start their seedlings indoors
- Transplant their seedlings outside
- Direct sow plants they won’t be starting indoors.
To help with this process, SHF has built a new planting dates calculator that does the math for you.
Why a planting dates calculator?
Calculating when to plant is one of the key decisions gardeners make each year, along with:
- Deciding what to plant
- How much to plant
- Where to plant (think crop rotation)
It can get pretty complex depending on how many plant varieties you start indoors.
The key factor in calculating when to plant is the last frost date, which is the latest date in the spring when killing frost is likely to occur. Seed providers – as part of their planting instructions — usually suggest that you plant seeds a certain number of days before or after the last frost date.
Most gardeners calculate the dates for each plant before the first year and make it a tradition thereafter. For example, you may start your tomatoes indoors on the fourth Sunday in April and transplant them on Memorial Day.
The SHF Planting Dates Calculator
automatically calculates when to start your plants.
If you’re anything like me, you want to start your garden as early as possible after a long winter.
One factor to consider is the impact of global warming. A traditional planting date calculated years ago may mean that you are planting later than needed. You might want to recalculate.
The SHF Planting Dates Calculator makes it easy to try a new last frost date and recalculate your planting dates whenever you would like. No more math. It’s fast and easy.
How it works
You start by selecting a last frost date (or you can let the SHF Last Frost Date Calculator do it for you). Then select your plants.
The result is a table with your plants and dates for planting seedlings indoors, transplanting seedlings outside or direct sowing. It also provides a link for information on seed options (from Amazon) for each plant you select.
If you use the Last Frost Date Calculator before using the Planting Dates Calculator, the app will automatically enter the last frost date.
Of course, date calculation is only a guide. The weather may turn out to be unusually cold, or the soil temperature may be too cold for transplanting or direct sowing. You may want to invest in a soil thermometer to test the soil temperature before you transplant. You can learn more about transplanting at the proper soil temperature in this article.
Adjusting the calculations
The Planting Dates Calculator uses the typical calculation for each plant. So, for example, it subtracts 10 days from the last frost date for direct sowing arugula (which is pretty hardy and can take cold weather). If you are really exacting and believe that your variety of arugula requires something different, you can manually adjust the dates.
So that you can make adjustments, here are the calculations used for each plant:
| Plant | Seedling Start | Transplant | Direct Sow |
|---|---|---|---|
| Artichoke | Direct Sow | Direct Sow | 21 Days After |
| Arugula | Direct Sow | Direct Sow | 10 Days Before |
| Asian Greens | Direct Sow | Direct Sow | 10 Days Before |
| Beet | Direct Sow | Direct Sow | Last Frost Date |
| Beans (Bush or Pole) | Direct Sow | Direct Sow | Last Frost Date |
| Broccoli | 56 Days Before | 14 Days Before | 7 Days Before |
| Broccoli Raab | Direct Sow | Direct Sow | 7 Days Before |
| Brussel Sprout | Direct Sow | Direct Sow | 7 Days Before |
| Broccoli | 42 Days Before | 7 Days Before | 7 Days Before |
| Carrot | Direct Sow | Direct Sow | 7 Days Before |
| Cauliflower | 56 Days Before | Last Frost Date | Last Frost Date |
| Collard Greens | Direct Sow | Direct Sow | 7 Days Before |
| Corn | Direct Sow | Direct Sow | 28 Days After |
| Corn Salad | Direct Sow | Direct Sow | 7 Days Before |
| Cucumber | 7 Days Before | 7 Days After | 7 Days After |
| Eggplant | 28 Days Before | 14 Days After | Start Inside |
| Endive | Direct Sow | Direct Sow | 7 Days Before |
| Gourd | Direct Sow | Direct Sow | 24 Days After |
| Kale | Direct Sow | Direct Sow | 7 Days Before |
| Kohlrabi | Direct Sow | Direct Sow | 7 Days Before |
| Leek | Direct Sow | Direct Sow | 7 Days Before |
| Lettuce | Direct Sow | Direct Sow | Last Frost Date |
| Melon | 14 Days Before | 14 Days After | 14 Days After |
| Mesclun | Direct Sow | Direct Sow | 7 Days Before |
| Microgreens | Direct Sow | Direct Sow | 7 Days Before |
| Mustard | Direct Sow | Direct Sow | 7 Days Before |
| Okra | Direct Sow | Direct Sow | 24 Days After |
| Onion | Direct Sow | Direct Sow | 7 Days Before |
| Parsnip | Direct Sow | Direct Sow | Last Frost Day |
| Pea | Direct Sow | Direct Sow | 7 Days Before |
| Pepper | 28 Days Before | 14 Days After | 21 Days After |
| Potato | Direct Sow | Direct Sow | Last Frost Date |
| Pumpkin | 14 Days Before | 14 Days After | Start Inside |
| Radicchio | Direct Sow | Direct Sow | 7 Days Before |
| Radish | Direct Sow | Direct Sow | 7 Days Before |
| Rhubarb | Direct Sow | Direct Sow | 7 Days Before |
| Salad Greens | Direct Sow | Direct Sow | 7 Days Before |
| Spinach | Direct Sow | Direct Sow | 7 Days Before |
| Squash | 14 Days Before | 14 Days After | Start Inside |
| Swiss Chard | Direct Sow | Direct Sow | Last Frost Date |
| Tomato | 28 Days Before | 14 Days After | Start Inside |
| Turnips | Direct Sow | Direct Sow | 7 Days Before |
| Watermelon | 14 Days Before | 14 Days After | 14 Days After |
| Watermelon | 14 Days Before | 14 Days After | 14 Days After |
| Zucchini | 14 Days Before | 14 Days After | Start Inside |
If you have questions or comments about the SHF Planting Dates Calculator, please feel free to use the comment section below. In the meantime, happy calculating!
Articles you may enjoy:
