Project Summary
- Hours of Operation: 4 to 8 hours
- Overall Duration: 1 to 2 weeks
- Skill Level: Suitable for Children
- Projected Expense: $0
Gradually acclimating plant seedlings to outdoor conditions involves exposing them to wind, sunlight, and rain, which strengthens them and reduces water loss when faced with these elements. This process is essential in avoiding transplant shock, a phenomenon where seedlings struggle, grow poorly, or perish due to abrupt shifts in temperature and sunlight. Continue reading to discover the steps for hardening off seedlings.
Contents
The appropriate time to acclimate seedlings to outdoor conditions.
Start the hardening-off procedure one to two weeks prior to the day you intend to transplant your seedlings outside. Generally, in the spring, seedlings are usually moved outdoors following the final frost date. Nevertheless, cold-tolerant plants can be set outside two to four weeks in advance of the last frost date.
The duration needed for seedlings to acclimate to outdoor conditions varies based on the plant species and the prevailing temperatures. Therefore, it’s important to remain adaptable during the hardening-off process and be ready to bring the seedlings inside or provide protection if there is a chance of a late spring frost or snowfall.
Here are two popular techniques for acclimating seedlings to outdoor conditions:
Requirements You’ll Need
Gear / Instruments
- Optional wheelbarrow
- Optional cold frame
Materials
- Plants cultivated indoors from seeds
Instructions
Acclimate seedlings by slowly introducing them to outdoor environments.
Initiate Exposure to Outdoor Environments
On a warm day with temperatures exceeding 45 degrees Fahrenheit, position seedlings in a sheltered outdoor spot, away from direct sunlight and wind, for one hour on the initial day.
Reintroduce the Plants Indoors
Bring the seedlings inside once they have reached their maximum outdoor exposure for the day, and position them in a warm location, such as a heated garage or basement.
Tip
Remember to safeguard young seedlings from pests like animals, snails, and slugs. Position them on a table or in a location that is out of reach of animals.
Enhance Visibility
Enhance the daily outdoor exposure for the seedlings by one hour to help them slowly adjust to the rising levels of filtered sunlight and breeze. The essential factor for success is to introduce them to the outdoor environment gradually. Avoid placing delicate seedlings outside on windy days or when the temperature drops below 45 degrees Fahrenheit.
Enhance the Quantity of Sunlight
Following a couple of days in a partially shaded area, you can move the seedlings to spots that get morning sunlight, gradually increasing their exposure to direct sunlight over time. Introducing very young seedlings to direct sunlight too early can damage their leaves. With each passing day, the seedlings will become more resilient to outdoor conditions.
Tip
If you choose to slowly adjust your plants to extended outdoor exposure, utilizing a wagon or wheelbarrow can simplify the process of transporting them back and forth between indoors and outside.
Keep Plants Outdoors Overnight
If the temperatures stay mild during the day and night (minimum of 50 degrees Fahrenheit), the young plants should adapt to more sunlight and can be left outside overnight. Ensure the soil remains moist in case the temperatures unexpectedly rise.
Transplant
Once your plants have spent seven to fourteen days adjusting to outdoor conditions, they can be moved to the garden or into containers. If you can, opt for a cloudy day for the transplanting. Be sure to water them thoroughly after planting.
Acclimate Seedlings in a Cold Frame
Relocate Your Seedlings
Transfer your seedlings to an outdoor cold frame approximately one to two weeks prior to your scheduled transplanting.
What exactly is a cold frame?
A cold frame is essentially a bottomless wooden structure topped with a transparent lid, typically hinged for easy access. It functions similarly to a greenhouse, with the key distinction being that the lid can be opened or closed to shield plants and gradually acclimate them to outdoor conditions.
Keep an eye on the temperature and humidity levels.
Ensure that the temperature inside the cold frame remains between 50 and 80 degrees Fahrenheit. While the seedlings are in this protected and warm setting, it’s important to keep an eye on the moisture levels in the soilavoid allowing the plants to become too dry.
Initiate Exposure Process
Disable the heating cables and/or keep the cold frame cover open for extended durations daily. Begin with three to four hours and progressively extend the exposure time by one to two hours each day.
Safeguard Vegetation During Nighttime
Shut the cover of the cold frame and turn the heating back on at night if the temperature falls below 40 degrees Fahrenheit.
Transplant
Seedlings will be prepared for transplanting within a week to two weeks. If you can, choose a cloudy day for the process. Be sure to water them thoroughly after planting.
What are the potential consequences of not acclimating seedlings?
Failing to acclimate your seedlings to outdoor conditions can significantly hinder their growth, potentially delaying your harvest by several weeks. In the worst-case scenario, the seedlings may perish, resulting in a loss of the time and resources you invested in germinating the seeds and nurturing the plants.
Which types of seedlings can skip the hardening off process?
Cold-hardy seedlings, like various lettuces and greens, tend to withstand transplant shock better. Nonetheless, it’s advisable to acclimate them gradually if possible. On the other hand, warm-season crops like tomatoes and peppers, which cannot tolerate frost, should always undergo the hardening-off process.
What are some effective methods for rapidly acclimating seedlings?
There are no true shortcuts when it comes to acclimating seedlings to outdoor conditions. Skipping or shortening the hardening-off process increases the likelihood of transplant shock. While you might experience favorable weather conditions, such as warmth and calm winds, taking the risk of a rushed hardening-off period could jeopardize the well-being of your seedlings.
Should you acclimate seedlings or plants purchased from a store?
The necessity of hardening off store-bought plants is contingent upon their previous environment within the store. Plants that were kept indoors or in a sheltered greenhouse require a hardening off process. Conversely, if the plants were exposed to the outdoors or situated in an open garden center, they are likely already adapted to the external conditions and do not require hardening off.
