Hardening Off Plants

When we have the benefit of full greenhouse grown plants, we need to make sure that they don’t get too stressed when planted in a different environment. Many times in the spring, this process is much quicker when the temps are cooler. The hardening off process is super simple and easy to do!

Hardening off of plants is the process of strengthening tender seedling and plants grown inside, in greenhouses, or under shade cloth, like our perennials. Hardening off thickens the cuticle of their leaves to avoid access moisture loss. If you are planting potatoes, onions, asparagus, strawberry bare roots, or anything completely under the soil you do not need to take these steps.

Slowly acclimating plants to lower temps, less humidity, and strong winds will reduce stress to your plant. Even if it shows small signs of stress, it’ll be fine!

How to harden off plants grown inside or in greenhouses:

Hardening off takes 1 to 3 weeks depending on the weather and your available time. When there is a very windy day, or quick rise in temps on clear sunny day avoid direct exposure when you are going through the hardening off process.

Each day after bringing seedlings outside, bring back inside and place in a warm spot.

*Best to do this when temps are 50F or above. Cold-tolerant plants can handle ~40F temps when starting this process.

1st day: Put your plants outside in a shady spot for 1-2 hours.
2nd day: Place in dappled sun or early morning sun for 1-2 hours.
3rd day: Place in dappled sun or full sun for 2-3 hours.
4th to 7th day: Increase full sun an hour or two each day. If overnight temps are warm enough (~50F) between the 4th-7th day, it’s usually safe to leave them outside in their containers.

Acclimate slower if you see signs of stress which can be quickly wilting in the sun, scorched leaves, and drooping. Movement from the wind is beneficial, but not in excess to cause complete drooping over for long periods.

Make sure you check soil moisture frequently. Water when the soil is partially dry so your plants starts developing roots that reach further down to a water source.

How to harden off perennials grown under sun protection:

When you buy plants grown under shade cloth that have already been exposed to wind and fluctuating temperatures, hardening off is focused on increasing sun exposure. Perennials grown under shade cloth (protection from direct sun), have already been exposed to fluctuating temperatures and wind.

If you see a plant grown under shade protection, you should acclimate them to their preferred sun exposure over a few days especially if the days are sunny and hot. Follow the first 3 steps above but keep the plant outside during the process. During cool spring weather or when the forecast calls for consecutive cloudy days it’s fine to plant in it’s permanent spot.


Transplanting can be a little stressful to plants. When you move plants to their permanent spot choose a cloudy day. Don’t forget to mulch around your plants to help with water retention as the top couple inches can dry out within a day if it’s windy and sunny.

Water your plants at 1″ – 1.5″ a week which is around 10 cups of water per square foot. If there is rain, you can reduce manual watering.