Did you plant seeds indoors or in a greenhouse? Are the seedlings a few inches tall, and do they have at least two to three sets of true leaves? If so, it is time to transplant the little darlings into the garden! But first, they will need to be hardened off. In this article, you will learn what hardening off is, why you need to do it, and the three easy steps to take to make the transplant successful.
What is Hardening Off?
Hardening off is the process by which seedlings grown indoors in a controlled environment are gradually acclimated to the variable growing conditions of the garden outdoors.
Why Do Plants Need to Be Hardened Off?
The hardening off process helps strengthen the seedlings by acclimating them to their new surroundings outdoors. If you do not acclimate the seedlings (a.k.a. young plants) to the harsher conditions found outdoors, they will experience stress, which weakens them and lessens their chances of survival.
How to Harden Off Seedlings or Young Plants
The hardening off process is not difficult, but it does take a little time. It is important not to rush the process if you want it to work.
Step 1
Start the process one to two weeks after the last frost date and when the outside temperature is at least 45°F (7°C). Place the seedlings outside in a shaded area that is protected from the wind for about one to two hours. Afterwards, take them back inside. Repeat this step for the first two to three days.
Note: Some crops that tolerate cooler temperatures can be planted in the ground a couple of weeks before the last frost date. (Here’s how to find the last frost date for your area.)
Step 2
For the next seven to ten days, repeat step one except leave them out for an additional hour each day. Morning sun is preferable early on, but as the week progresses, they can be exposed to warmer, afternoon sun and light breezes.
If the plants, like oxalis for example, prefer shade to part shade, place them in an area that receives dappled sunlight instead of full sun.
Be sure to keep an eye on the plants. If the soil starts to dry, they will need to be watered. Bring the plants indoors at the end of each session. If it gets too windy, relocate them to an area that offers more protection.
If the temperature drops below 45°F (7°C) or it is too windy, skip that day and try again the next. While cool season crops like lettuce, spinach, broccoli, cauliflower, and Brussels sprouts can withstand cool temperatures, that is true only if they are in the ground. To be safe, seedlings and young plants that are still in small pots or trays need to be brought indoors if temperatures drop below 45°F (7°C).
As the plants grow stronger from exposure to the sun and gentle breezes, you can slowly reduce the amount of water they receive. Just be sure to keep an eye on them because you do not want them to be stressed. If they show signs of wilting, they are not getting enough water.
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Step 3
Once the plants have completed the seven to ten day acclimation process, they are ready to graduate to living full time outdoors, that is, as long as the temperature remains above 45°F (7°C) during the day and night. If the temperature drops or it becomes windy, take the plants back inside. On the other hand, if it becomes too warm, you may need to relocate the plants to an area with less sun. Alternatively, you can try adding a shade cloth or a row cover so as to protect the plant’s leaves from scorching.
When these steps have been completed, it is time for them to be transplanted into the garden! Keep in mind that after the plants have been placed in the ground, raised beds, or grow bags, they may still experience some mild shock. This is completely normal.
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