When to Plant Seeds? A New Planting Dates Calculator


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.

Planting Dates Calculator

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:

Days from Last Frost Date
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:

  1. Transplanting Seedlings Outdoors
  2. When to Start Seedlings Indoors
  3. Starting Seedlings Indoors in Summer
Summary
Article Name
When to Plant Seeds? A New Planting Dates Calculator
Description
Learn about the SHF Planting Dates Calculator. It makes it fast and easy to calculate when to start seedlings indoors, transplant seedlings and direct sow.
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