How to Know When Seedlings Are Ready to Go Into the Ground

As the weather gets warmer and the days get longer, we get anxious to start gardening. When to plant our seedlings is an excellent question, and one that depends on a few factors: type of plant, last frost date (or weather), size of seedlings, and proper hardening-off of seedlings.


One important thing to consider before planting is to understand what type of plant you want to grow. Some plants are cold hardy and will tolerate colder weather. Potatoes, lettuce, onions, kale, broccoli, radishes, will all take a bit of cold and are usually planted first, before the last frost date has passed.


Tomatoes, cucumbers, peppers, eggplant, squash on the other hand, are warm weather plants. They will not tolerate cold weather and they need warmer nighttime temperatures to thrive in your garden. It’s usually a good idea to wait until after your last frost date to plant warm weather seedlings.

The next vitally important step is to know the average last frost date for your area. If you don’t know, go to Dave’s Garden and put in your zip code. The average last frost date for my area in Eastern Iowa is between the end of April and the middle of May. However, it seems like we get a killing frost every year around or after May 15.


Now that you have a range of when you could plant seedlings, to start watching the long term forecast a couple weeks before your last frost date. The soil temperature needs to be warming, and the long-range forecast of overnight lows should be in at least in the 40s for warm weather seedlings. I have killed a lot of warm weather seedlings by planting them too early, so be very careful when deciding to plant!


Now that you know to carefully watch the weather before putting seedlings in the ground, let’s think about your seedlings. Most seedlings are ready to go in the ground after they have three or four sets of true leaves. If you’re starting seedlings at home, you want to make sure they have real leaves and not just the first leaves that emerge after they germinate.


Your seedlings also need to go through a process called hardening-off. During this process, you slowly acclimate tender seedlings to be able to accept the wind and sun they will experience when you put them outside. If you don’t harden them off properly, they won’t make it. Learn how to harden off seedlings here.


Once it’s warm enough, and your seedlings have been hardened-off properly, you can go ahead and plant them in the garden but continue to watch the weather just in case! You never know when a blast of cold air is coming unless you pay attention, especially at the beginning of the growing season.


If you’re looking for tips on growing specific vegetables, I have a lot of helpful garden posts on Simplify, Live, Love!

Published by Michelle Marine

I'm a semi-crunchy Eastern Iowa mom of 4 crazy kids on a quest to stay sane and healthy. We try to live a sustainable lifestyle on 5 acres with chickens, dogs, rabbits & more! Grab some coffee or wine and hang out for a bit!