How you can Harden Off Seedlings: 7 Easy Suggestions


Whether or not you decide up some seedlings out of your native nursery or begin some at house, chances are you’ll wish to plant them outdoors as quickly as potential. However transferring them from their cozy, protected house to a harsh outside surroundings causes stress. Hardening off seedlings permits them to acclimate to their new house to allow them to thrive.

Correctly acclimating your seedlings requires endurance and a few know-how, however it’s a simple course of. Merely put, it includes slowly growing their time outdoors till they’re able to transplant. Nevertheless, figuring out some useful suggestions makes the method simpler.

I’m going to share some hardening-off suggestions I’ve discovered whereas making ready hundreds of seedlings for his or her lives open air.

What Is Hardening Off?

On a metal garden table, an assortment of seedlings in pots of varying shapes and colors creates a lively display. The pots, with their distinct hues and designs, showcase a mix of plant types and growth stages.
Hardening off is steadily acclimating crops to new environments to stop shock.

If you happen to spend time at a nursery or vegetable farm, you’ll shortly grow to be acquainted with the time period “harden off.” However what does it imply?

Hardening off is plant communicate for slowly toughening crops to new environments. Gardeners usually harden off greenhouse-grown crops earlier than planting them of their new outside houses. This course of limits what gardeners name transplant shock and prevents points like dropped leaves, stunted progress, and discoloration.

Whereas engaged on vegetable farms, I shortly discovered hardening off seedlings was essential to the crops’ long-term success. You can begin with perfect-looking seedlings, however they’ll usually deteriorate after planting in case you fail to harden them off.

It is best to harden off each seedlings you begin indoors at house and people you buy from a nursery or huge field retailer. Except the seedlings develop in an unprotected outside surroundings, they most likely haven’t been hardened off.

What Occurs Throughout Hardening Off?

Rows of plant and flower seedlings nestled in rich, dark soil. These seedlings were lovingly started indoors, sprouting into young plants ready for the garden, displaying a variety of leaf shapes and shades.
Hardening off affords benefits like boosting the manufacturing of leaf wax.

We all know hardening off permits crops to acclimate to their new houses. However what’s occurring contained in the plant?

The stress of a brand new surroundings causes plant progress to sluggish. Crops additionally develop a thicker layer of wax or pure oils on their leaves, resulting in decreased water loss. You’ll additionally discover crops grow to be extra inflexible attributable to elevated lignin in cell partitions. Lastly, the quantity of water in cells decreases because the dry matter will increase.

If you add all these components collectively, you’ll discover that your crops can higher face up to environmental stressors like wind, direct mild, and drought.

Suggestions for Hardening Off Seedlings

Now that you realize what hardening off is, let’s evaluation some tricks to make the method simpler.

Wait Till the Climate Warms

A close-up of organic lettuce seedlings, displaying vibrant green leaves. Sunlight gently illuminates the tender plants, casting a soft glow on the healthy, young leaves, showcasing their lush growth.
Wait till temperatures persistently exceed 50°F earlier than beginning the hardening-off course of for seedlings.

Whilst you could also be itching to plant your seedlings in your backyard, don’t view the primary heat day as a name to maneuver your crops open air. If you happen to begin the hardening-off course of too quickly, seedlings should take care of tense chilly temperatures.

I like to attend till the daytime temperatures are persistently above 50°F (10°C) earlier than starting the hardening-off course of. I additionally hold the long-range forecast in thoughts.

For instance, I don’t place my seedlings open air if I expertise a heat spell in February. My space will nonetheless expertise below-freezing temperatures that will stress the seedlings. As an alternative, I wait till the climate is heat and inside just a few weeks of the final predicted frost date. Ready till this time means there’s a very good likelihood the climate will likely be heat sufficient to plant seedlings open air as soon as they’ve hardened off.

If you happen to’re uncertain when to start out, wait till the final predicted frost date arrives. Even when an unseasonably late frost arrives, you possibly can transfer your seedlings indoors.

2. Don’t Rush the Course of

An arrangement of numerous small black pots, each nurturing a tender seedling, with corresponding labels identifying the plant type or variety. The labeled pots present a systematic approach for tending to and tracking the growth of diverse seedlings.
Step by step improve outside publicity for seedlings over 1-2 weeks for optimum acclimatization.

Keep in mind, the entire level of hardening off seedlings is permitting them to regulate to their new surroundings. If you happen to seize a seedling tray from a greenhouse, let it sit outdoors for an evening, after which plant the seedlings in your backyard, the crops will nonetheless expertise a lot of stress.

A greater possibility is to slowly improve the time crops spend of their new house. I like to extend the seedlings’ time open air by just a few hours every day. Meaning the entire hardening-off course of takes between one and two weeks.

For instance, I’ll place my seedlings in a protected outside surroundings for one or two hours on the primary day. A chilly body is right, however you too can use a flippantly shaded, protected space. A coated porch works nicely, as does an space shielded from wind by a home or row of shrubs. After the crops are outdoors for just a few hours, I return them to their protected indoor surroundings.

On the second day, I place the crops in the identical location and allow them to keep outdoors for 3 or 4 hours. I observe this sample till the crops spend all day and night time outdoors (offered nighttime temperatures don’t dip under freezing).

At this level, I transfer the crops to a spot that mimics their finish location. That usually means an open space with full solar. After the seedlings spend just a few days on this location, they’re able to plant!

3. Pay Consideration to the Wind

In the foreground, a striking plant displays leaves in shades of purple and muted green. The background, deliberately blurred, offers a vivid contrast of lush, vibrant green foliage, creating a compelling visual juxtaposition of color and depth.
Keep away from exposing seedlings to winds over 5 mph initially, and canopy them if robust winds come up unexpectedly.

Whereas ten-mile-per-hour winds might not appear to be an enormous deal to you, they are often stunning to tender seedlings! Keep in mind, these seedlings have lived a pampered life with restricted publicity to parts like wind, chilly temperatures, or heavy rains.

Regulate the climate forecast, and keep away from setting seedlings outdoors when winds are above 5 miles per hour. Whereas seedlings can deal with wind after just a few days outdoors, avoiding wind through the first few days of the hardening-off course of is greatest.

If surprising excessive winds arrive just a few days into the method, cowl the crops with row cowl to dampen the affect.

4. Maintain Seedlings Effectively Watered

A red watering can showers water onto a single seedling, nestled among various other seedlings, all basking in the warmth of sunlight. The droplets from the can create a shimmering effect as they hit the soil around the plants.
Correct watering through the hardening-off course of minimizes stress for transitioning seedlings.

Transitioning seedlings to a brand new surroundings is tense, and also you wish to restrict stress as a lot as potential. Appropriately watering the crops eliminates stress attributable to dry or water-logged soil.

Keep in mind the variations between an indoor and outside surroundings affect the quantity of water your crops require. Subsequently, you’ll probably want to change your watering schedule after you progress your seedlings open air. Whereas you could have watered your indoor seedlings as soon as a day, outside solar and wind might require you to water them two or 3 times per day.

The tip purpose is to hold the potting soil moist however not moist. Some dry soil toughens the crops, however utterly dry soil causes an excessive amount of stress.

5. Don’t Neglect to Harden Off Summer season Seedlings

A black plastic tray rests on green grass, holding potted flower plants of various colors and sizes. In the background, the ground reveals tiny emerging seedlings, appearing blurred against the landscape.
Gradual acclimation helps summer season seedlings easily transition from a greenhouse to an out of doors backyard, decreasing stress.

Greenhouses are nice for planting seedlings. Most individuals notice a winter greenhouse’s cozy and heat surroundings differs from the windy and cooler surroundings outdoors. Nevertheless, there are additionally variations between a summer season greenhouse and an out of doors backyard.

In the summertime, greenhouses present a little bit of shade and reduce the sunshine depth. That is very true if greenhouses or propagation tunnels are coated with shade fabric. Together with variations in mild, you possibly can count on variations in wind and rainfall.

If you happen to take away summer season seedlings from the greenhouse and instantly plant them in an out of doors backyard, the crops will expertise pointless stress. They might grow to be sunburned attributable to elevated mild or wilt attributable to drying winds. Subsequently, it is best to take the time to harden off summer season seedlings like spring seedlings.

Slowly expose them to elevated mild and extra time in a sizzling and windy surroundings. Whereas it might appear pointless, hardening off will increase the possibilities summer season seedlings will thrive.

6. Contemplate Plant Sort

Two gray pots, each with a young tomato seedling, displaying green leaves and delicate stems. These young plants, thriving in their pots, manifest the promise of future robust growth and bountiful produce in a garden settin
Cool-weather crops deal with decrease temperatures nicely, whereas warm-weather ones want extra care throughout hardening off.

Whereas no seedlings ought to be uncovered to below-freezing temperatures, some are extra cold-tolerant than others. Cool-weather crops like lettuce, broccoli, spinach, and kale can tolerate chilly temperatures higher than warm-weather crops like tomatoes, cucumbers, and squash.

Meaning you need to be extra cautious with warm-weather crops than with cool-weather crops. Whereas kale seedlings can deal with a forty five°F (7°C) day just a few days into hardening off, the identical climate severely stresses a cucumber seedling.

The plant kind additionally impacts when it is best to start. I usually harden off crops like kale, lettuce, inexperienced onions, and bok choy earlier than the final frost arrives. So long as the seedlings are slowly acclimated to the outside, they’ll survive a frost with assist from row cowl. Nevertheless, frosts stress and stunt tomatoes, eggplant, and peppers, even in case you’ve correctly hardened them off. 

7. Defend Crops After Transplanting

Two small greenhouses stand side by side, sheltering neat rows of lush, leafy vegetables. The compact structures are made of transparent panels, allowing ample sunlight to filter through, nurturing the thriving green plants within.
Hardening off reduces transplant stress, however additional safety post-transplant should be needed.

Correctly hardening off seedlings decreases the stress they’ll expertise throughout transplanting. Nevertheless, that doesn’t imply it utterly eliminates transplant shock.

Even in case you harden off your seedlings, you should still want additional protecting measures after transplanting. For instance, in case you transplant bok choy or kale within the spring and an surprising freeze arrives just a few days later, it is best to defend your crops with row cowl. It will permit the crops to proceed to regulate to their new surroundings with the least stress potential.

I typically want to assist summer season crops adapt to their new sizzling houses. Since I plant fall crops like kale, broccoli, and lettuce in August, these cold-hardy crops usually must take care of excessive temperatures and intense solar. I cowl the crops with shade fabric and irrigate every day if I take care of sunny, dry situations and temperatures above 90°F (32°C). After per week within the floor, the crops can take care of these situations.

Closing Ideas

Hardening off seedlings is an important a part of rising comfortable, wholesome crops. If you happen to acclimate your crops over per week or two, they’ll be able to thrive of their outside house.

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