Frost Dates & Hardiness Zones

Lets talk frost dates and what they tell you in relation to the garden. First and last frost dates help when it comes to planning when frost sensitive plants can go into the garden. On the other end of the season, they tell us when our frost tender plants should be done for the season. This shows us the latest time we should have transplants or seeds in the garden for the plant to reach maturity before the first frost. They can also help you determine when frost hardy/cold hardy plants can go outside. There are many plants that you can direct sow or transplant before your last frost date and there are many plants that need to wait until all danger of frost is gone. Knowing plant families and each plants needs will help determine which plants fall into which category. (With a few exceptions most plants in a plant family will have similar needs.) Notice how gardening zone doesn’t come up here? Gardening zone is good to know when it comes to perennials, not annuals, which is what makes up most kitchen gardens. When I see someone state their gardening zone, it just tells me they either have a colder or warmer winter than me, nothing about when they should be planting transplants or sowing seeds. (Gardening zone tells you the average coldest temperature for an area.) They can give a slight indication that the persons growing season is shorter or longer, but that isn’t always the truth. When helping a coaching client I ask about frost dates to determine the frost free growing season, not about hardiness zones, unless they are needing help with perennial plants.

When it comes to seed starting, you can start seeds in relation to frost days and soil temperature as well as the Arc of Seasons. Starting most seeds either 6-8+ weeks before your last frost or longer for things like onions or peppers that need a longer time. (Medicinal herbs are a completely different story, I’m talking about kitchen garden annuals.) When direct sowing, seed packets will likely tell you how many weeks before your last frost to sow seeds. With a bit of research you can create a document that roughly tells you when to start each plant variety. You can also add dates for when each plant should be transplanted into the garden. Warm weather plants that are frost tender are most often transplanted into the garden 1-2 weeks after last frost dates to help ensure their success. (Always have a frost plan in place, you never know when a late frost will strike.) For anything that is frost hardy, look at air temperatures and soil temperatures then direct sow based on those numbers instead of frost dates. 

Something else that you need to know when planning your garden is your heat days, days where your average daily temperatures are above 85°F+ because this is when things start to suffer in the heat. Tomatoes can drop their blossoms as well as beans, etc. things like okra or sweet potatoes can tolerate this kind of heat more. High temperatures essentially throw your plants into dormancy until the temperatures drop back down. This is crucial to know so that you sow seeds in time so that your plants reach maturity before your heat days arrive. It also helps you know when to avoid planting out fall crops that will go straight to seed with high temperatures. Knowing your first frost date tells you when you need to have your warm weather plants harvested and done by. You will work backwards from your first frost date to make sure whatever frost tender plants you are planting will have reached full maturity before that date. It also helps with planning your fall garden because you will want to have your fall crops well established before frost hits, even for frost hardy plants.

Knowing you frost dates helps with planning your garden. Knowing your average temperatures of both soil and air also play a big part in planning. Paying attention to days where your temperature is too high for production plays a key role as well. Hardiness zone comes into play only when you are dealing with perennial plants. It tells you whether something can make it through your coldest temperatures and come back again. I hope this help you with your garden planning.

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