How to Harden Off Plants

how to harden off plants

When you buy houseplants from a nursery or a store, those plants are familiar with living inside. If you plan to keep the plants inside your home or office, these plants will be familiar with this setting. However, if you plan to move these plants to your outdoor garden or patio, you need to “harden them off” to help them transition.


So what does hardening off a plant mean, what are some steps, and why is it important? Here is the complete breakdown and more below!


What Does “Harden off Plants” Mean Exactly?

what does harden off plants mean exactly

Hardening off seedlings means a gradual transition for tender plants to acclimate outdoors. Hardening off is a slow and gradual process where on the first day, you put the plant outside for an hour with protection from wind and rain. As the days go by, you leave the plant out for a bit longer and let it experience more elements.


Some elements that you want the tender plants to experience include cloudy days, full sun, wind, and eventually cool nights. The gradual process of letting your plants experience the outdoor elements reduces transplant shock. Just like bringing a plant from a nursery to your home, you want to ease the plant into its new outdoor conditions.


What if You Don’t Harden Off Plants?

what if you don't harden off plants

If you decide to put an indoor plant outside, it will have transplant shock. The indoor plant is unfamiliar with normal outdoor conditions, so it will enter survival mode. Going into survival mode can work for some plants, but not all plants adapt to the new surroundings quickly, which causes wilting.


Your best bet is to give your plants ample time to adjust to their new outdoor surroundings. Giving the plants exposure to direct sunlight for a couple of hours is essential, especially if the plant is only familiar with grow lights for light. The same allows the plant to experience rainwater, wind, and outdoor bugs.


When to Harden off Plants

when to harden off plants

Your best bet is to give your plants between one and two weeks to go from indoor to outdoor plants. Spring usually works the best to transition because the days are warmer, and the nights aren’t too cold to cause temperature shock. If you live in an area with cold nights during the spring, you can cover the plant with a cloth or structure to limit frost protection.


Another tip for hardening off your plants is to wait for germination. Germination is how growth occurs on the plant from seeds or spores. Once the plant produces the flowers and leaves, you can start hardening off since significant growth has already happened.


Why is Hardening Off Plants Important?

why is hardening off plants important

Transplant shock is a common problem for plants. Young plants and baby plants need a gradual change in environment to adapt to their surroundings. If you take an indoor plant and move it outside the next day permanently, the plant will struggle to adjust to the new environment. Going into transplant shock can stop growth since the plant is in survival mode and ultimately wilt and die.


A Sample Schedule for Hardening Off Plants

While there is no exact hardening off schedule to follow, here is a sample process to consider. You should begin this operation in the spring when the daytime temperature is above 50 degrees, and the nighttime is above 40 degrees Fahrenheit if possible. As a note, every plant will need a different amount of time to adjust to outdoor living.


Day 1:

Move the plant outside for one hour. Ensure that the plant is in an area that won’t have direct sun or wind. A safe place to put the plant outdoors is on your backyard porch so animals can’t get to it. After an hour outside, you bring the plant back into your home or office.


Days 2 – 5:

day 2-5 hardening off plant

Put the plant back outside for an additional hour in the same spot. As each day goes by, you can increase the length of time by an hour each day. If you notice the plant is not experiencing the direct sun, you can move it to a sunny area for a bit. Remember that you don’t want to leave these plants under the full sun for too long as they are still acclimating to the outdoor conditions.


To help with acclimation to the outdoors, you can water these plants while they are outside. Watering the plants gradually as they are out in the sun can help the plant get familiar with water and sun at the same time. Also, it is ok if bugs start to come to this plant as this is a way for the plant to familiarize itself with outdoor insects.


Days 6 – 8:

days 6-8

You can keep the plants outside until it gets dark. Now that you are in a week within this schedule, you keep the plants out for several hours. The plants are familiar with sun, wind, getting water, and now experiencing climates like overcast and sunny days. The mix between environments will be critical for these plants when they eventually stay outside.


Days 9 – 14:

As long as the nights will be above 40 degrees Fahrenheit, if possible, you can leave your plants outside at night in the area you plan to keep them. Having the plants stay where you will eventually leave them or plant them can help them acclimate to an all-day outdoor lifestyle.


Can You Harden off Plants in the Rain?

can you harden off plants in the rain

Light rain works well for hardening off plants after a few days of introducing the plant to the outdoor climates. However, if you expect strong winds and heavy rain, you should protect the plant by bringing it back inside. The strong winds and or rains might cause structural issues for the plant, especially with it is starting to adjust to the outdoors, so you don’t want to damage it by keeping it in that harsh environment.


Should You Harden off Plants Entering a Cold Frame?

If you own a cold frame or unheated greenhouse for your plants, you can follow the same steps above to introduce them to this environment. Just like before, you want to start with one hour of this new environment and then gradually let them settle into this home after a week or two.


Signs that it is Not Working

An early indicator that the hardening off-plan is not working is when plants wilt and or experience burns. Wilting signals that the plant is not adjusting to the new environment, so it starts to fall over to the side.


Leaf burning is another example of the plan not working. If you put the plant outside in an area with direct sunlight for too long, it might cause leaf burn. Leaf burning is especially true if the plant is familiar with indirect light or grow lights, and you immediately give it direct sun for too long.


Conclusion: How to Harden Off Plants

In summary, hardening off plants means a gradual process of introducing indoor plants to the outdoors. By slowly giving plants full sun, wind, bugs, rain, and more, you allow the plant to familiarize itself with being outside permanently. Then when the plant is ready to enter your outdoor garden bed, mulch, or patio, it will already be familiar with outdoor living and won’t go into transplant shock.


As a note, you can use this same process with things like tomato plants and cucumbers to add to your vegetable garden. The whole point is when you move indoor plants outside, you want to do this in a gradual and slow process.


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