What is Hardening Off

Hardening off is the gradual process of taking your seedlings from the indoor environment under the grow lights to slowly exposing them to the outdoor environment before planting out in the garden.

Here’s an example of me hardening off my seedlings here.

Why Hardening Off Matters

The importance of hardening off seedlings is that it helps strengthen seedlings. You risk killing your plants if you take them directly from indoor grow lights to out in the garden. This is because the light intensity of the sun and the outdoor wind is too intense. The outdoors also has large temperature swings from day to knight in comparison to an indoor environment that stays a consistent temperature.

When to Start Hardening Off

The optimal timing in relation to seedlings age and weather conditions. Start the hardening off process approximately 2 weeks before the last frost date. This time period will allow your plants time to acclimated to the outside elements.

Choosing the Right Gradual Temperature

It’s important to take out seedlings out gradually. You’ll want to take them out once day time temperatures start reaching above 50 degrees. Take your plants outside for short periods at first, one-two hours at first gradually increasing the time outside over a matter of days. It’s so important not to skip this step so you don’t risk killing your seedlings.

Protecting Seedlings During Hardening Off

You will want to protect your plants wile outside from intense sun and wind. I like to place mine under our patio table, chairs or umbrella at first, then gradually bring them out into the full sun on the patio table. If it’s a particularly windy or rainy day you many just choose to skip taking them out that day.

Monitoring and Adjusting

It’s important to keep observing your plant’s response to the gradual exposure to the outdoors and adjust as necessary. For example, if your tomato plant looks droopy after being outside, be sure to water it and get under the grow light.

Common Mistakes to Avoid

The most common mistake people make in this hardening off process is too much outside time at once. Remember to make this a gradual process and check on your plant’s response often.

Transplanting after Hardening Off

Once your danger of frost has passed and you’ve acclimated your plants to several weeks of hardening off, they are ready to be planted out in the garden. Most people say they like to plant out on a cloudy day or later in the evening to prevent frying their plants.

Ensuring Healthy and Resilient Plants

Ensuring healthy and resilient plants begins with the right transplanting techniques. Follow these key steps—timing, gradual exposure, protection, and monitoring—to avoid common pitfalls and set your seedlings up for success.

Ready to get started?

Review the essential transplanting tips, gather your supplies, and take the next step toward a thriving garden today! process of transplanting your hardened off seedlings is not hard (pun intended) if you follow the measures of timing, gradual exposure, proper protection, monitor and adjust as needed, avoid the common pitfalls and transplanting in the garden at the right time.

Happy Seed Starting! Michelle

About the Author

Michelle is a self-taught kitchen gardener whose goal is to help everyone find resources, guidance, and inspiration to rediscover or discover for the first time how fun and rewarding gardening can be.

Through her blog and social media, Michelle’s Garden Grows, she offers practical tips, educational content, and inspiration to support and encourage others on their gardening journeys.

With an RN, BSN degree, Michelle blends her faith and nursing background with gardening, showing how the garden can be a place of healing, growth, and renewal. You can learn more about Michelle’s Garden Grows here.

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