Harden Off Plants: What It Means and Why It’s Important!
We’ve been hardening off plants for the past two weeks in preparation for spring planting. Normally this process only takes a week or so but the weather isn’t cooperating. Generally, I like to have my tomatoes and peppers planted by mid-March. This isn’t unreasonable for our part of east Texas. But Mother Nature is having a moment right now. Correction…she’s having a total conniption!
In case you’re not familiar with the term, “hardening off” is the process of getting young, in-door plants accustomed to the outdoors. It’s a simple process that only requires a little of your time to complete. So grab a cup of coffee and sit a spell while I share how to transition young plants to the garden safely and why hardening off is an important step that shouldn’t be skipped.
What does “harden off” mean?
Hardening off is the process of gradually acclimating indoor plants to outdoor conditions. It is an essential step that will help young plants grow bigger and stronger once they’re planted in the garden. Hardening off is a gradual process that exposes tender, young plants to local outdoor growing conditions. This gradual process also helps in preventing transplant shock.
Hardening off shouldn’t be confused with “damping off”, which can be fatal to young seedlings. Hardening off is a positive thing and should be viewed much like sending a child off to school for the first time. You’ve done your best to prepare these plants for the big, wide world and now it’s time to set them free…in the garden!
What is the process for hardening off?
You should start the hardening off process on a still, cloudy day when temperatures are steady and mild. Water plants early in the day before they go outside. Once outside, place them in a sheltered spot, out of direct sunlight, for just 2 hours and then bring them back inside. On the second day, leave them out for three hours with one of those hours spent in dappled sunlight before bringing them back inside.
By the third day, increase the length of outdoor time to four hours with two of those hours spent in dappled sunlight. On the fourth day, move the plants to a location where they can get morning sun and afternoon shade. Now they are ready to be left outside all day.
Potted plants dry out quickly so continue to water them as needed and bring them in each night. Continue this process for at least seven days. If there’s no danger of frost and temps stay above 50 degrees at night, plants are safe enough to be left outside all night.
Plants that benefit from hardening off:
Some cold-hardy plants, like cabbage, don’t need to be hardened off and can go directly in the ground. Others, like my heat-loving peppers, do better with a gradual transition. Ideally, the majority of young plants that have been grown in sheltered conditions should be hardened off. That includes purchased plants. Most all plants from a garden store likely had their start in a greenhouse so this process would be adviseable.
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When should hardening off begin?
For most plants, it’s best to start hardening off a week to ten days before you intend to plant outside. That should be about a week before the final frost date. But don’t use that as your only indicator. Weather patterns can change overnight and frost can come a day early or a week late. So plan accordingly.
Hardening off tips and tricks:
The best place to harden off plants is in a shady, sheltered spot safe from strong winds. If a desirable location isn’t available, use boxes, buckets, hay bales or whatever you have handy as a wind break. If possible, avoid placing plants directly on the ground. They can become easy targets for children and pets. It’s also a protection against slugs and other curious critters (like chickens)!
It may be a hassle to move plants in and out everyday but your plants will thank you for it. Using a tray, cardboard box, rolling cart or a child’s wagon makes things so much easier. I love these large tubs! They’re so versatile that I bought several of them. Aside from moving plants, I use them for holding the seedlings while they’re under grow lights. This makes watering a gazillion small plants at one time so much easier! And since they’re already in the tubs, I don’t have to waste time when it comes to moving the plants outdoors.
These tubs are also good for mixing soil when filling pots. It keeps the soil contained and cuts down on scattered, wasted soil. They double as a planter for short season, shallow crops like radishes; for toting garden weeds to the burn pile; watering the critters and as a dust bath or miniature swimming pool for the chickens on a hot day! I’m sure you could probably come up with a few uses yourself!
More tips for hardening off:
Stay alert for unexpected cold snaps once plants are in the ground. You’ll need to cover tender plants if necessary. Young plants are susceptible to sudden weather changes. That’s why smart gardeners grow more plants than they need…in case the worst should happen.
You can use row covers, plastic sheeting, buckets, cardboard boxes, old milk jugs with the bottoms cut off…whatever fits over the plants easily. Just make sure you keep them close to hand. You’ll want to grab them quickly in case of frost or an unexpected drop in temperature.
Potted plants tend to dry out faster so ensure young plants get the water they need during the hardening off process. When possible, water from below. That means to water the soil and not the leaves so as to avoid mold and mildew growth.
Are your plants ready to go outside but the weather isn’t cooperating? Use an oscillating fan set on low to mimic a gentle breeze. This helps the plants to develop a stronger stem so they’re better able to handle breezy, outdoor conditions.
If your plants are sitting on a grow mat or some sort of heat source, start turning it off for a short time each day, gradually increasing the “off” time until they’re ready to head outdoors for the hardening off process. If a sunny window isn’t available, continue to provide a light source for at least 16 hours a day and turning it off at night.
Using a cold frame to harden off:
Cold frames are great for hardening off. Just make sure temps inside the cold frame don’t go above 80 degrees during the day or below 50 degrees at night. The good thing about a cold frame is that it solves the hassle of moving plants back and forth every day. It also means you don’t have to wait until just before last frost to start the process. You can start according to your schedule!
The process for using a cold frame is pretty much the same. Open the frame for one hour on the first day, gradually increasing exposure each day until the weather is mild enough to leave the cold frame open at night. Don’t forget to provide shade for the first few days. Close the cold frame if nightly temps fall below 50 degrees.
Is hardening off really necessary?
Plants that are not hardened off can suffer from transplant shock. Transplant shock is known for delaying growth, stunting or killing young plants. Putting young plants into soil that hasn’t warmed up sufficiently can be similar to jumping into a frozen lake after leaving a sauna. Too much direct sun exposure in a short amount of time can scorch young, tender leaves. This is much like a human who gets sunburn.
Think of it this way: failing to harden off young plants is similar to you moving from a sunny beachside to the frozen tundra…without a parka! If you need time to adjust to changing conditions, you can bet your plants do too!
In Summary….
Hardening off young plants should be done gradually over several days. Unless you’ve been using a fan to provide a gentle breeze, avoid hardening off on really windy days. It’s also a good idea to avoid hardening off when night time temps are below 50 degrees.
Hardening off that is done correctly can prepare plants for the garden within 7-10 days. When you’re ready to put your plants in their permanent location, do it on an overcast day and water thoroughly afterwards. Until young plants develop strong roots and become established, make sure to keep an eye on the weather and keep your plant protectors handy.
You wouldn’t send a child off into the world without preparing it in some way. So give your plants the same love. After all, you’ve already spent valuable time and effort in preparing the soil, planting the seeds and nurturing the sprouts. A few extra days shouldn’t be a burden. Eventually, your plants will repay you for all your hard work!
If you found this information helpful or if it left you with more questions, I’d love to hear from you. Just drop a comment below!
Until next time,
lisa
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