Hardening Off Schedule
Tis the season for trying our patience. And this topic is a perennial must-cover because for many new gardeners this process is confusing. And even for seasoned gardeners, it’s often rushed or even, gasp, a fleeting day before the planting itch is irresistible.
I’ve been thinking about how to make this process straightforward for everyone, and this is my best attempt. If you know me, you know that I am anything but a straightforward kind of person with writing and speaking, so bare with me. I hope this makes sense to all of you!
This is a 10-day process. It’s designed to slowly acclimate your plants to full strength sunlight. And also, by design, it will test your patience and may cause logistical headaches, the latter of which I try to workaround as much as possible. Sure, it’s possible to shortcut the 10-days, but there’s risk involved. I may use cloudy days around Day 8 as my green light to transplant, but I won’t ever risk it will full sun days and just throw them out into the wild before getting a really slow ramp up to the scorching full sun garden light.
Some highlights:
Cloudy days are my absolute favorite for hardening off. They are softer light, and thus we can be looser with the amount of time outside. If days are cloudy, I set my starts outside under some row cover all day long. It can be that easy, but we need clouds to navigate with ease.
Create a part to full shade scenario if you need to leave them out all day and can’t tend them. I know many of us can’t be home all day to pamper our seedlings. I personally prefer agribon/fabric row cover over shade cloth for this time of year as it adds frost protection and will create a bit of a hot house while also lowering the light transmitted.
Using row cover will create a light shade — the more layers you add, the more you’re cutting sunlight. I will layer them for a couple of reasons. First, because if it’s going to be cool, more layers will mean more warmth. Second, If I want to leave them out all day, on a cloudy Day 1, I will cut the light by about 40% by doing AG30+AG19. Shade cloth will also work but it’s not a frost blanket, so that’s why I use agribon (also called row cover) for this purpose.
Temperature: For cold hardy crops, I start this process when days will be above 40 for highs. For warm season crops, I prefer to begin this process when days will be close to 50F (10C) or warmer. These are minimum temperatures. I will keep brassicas and alliums out overnight down to a freeze, usually covered to keep their momentum going strong. For tomatoes and peppers and such, I will more likely bring them inside overnight if temps will drop into mid to upper 30s here. If I’m feeling crazy, I will leave them out, covered, under. the row cover as described below.
Shade is the way for the first half of my hardening off schedule. I don’t see a need for full sunlight until close to a week in. This will all but guarantee zero sunscald, which is irreversible foliar damage. Why risk it?
AG30 cuts out 30% sunlight
AG19 cuts out 15% sunlight
AG15, which is a lightweight insect protector and not a frost blanket, cuts out 10% sunlight
6 mil poly cuts between 10-12% sunlight
Day 1
Is it sunny? If yes, limit full sunshine to no more than 60 minutes. Alternatively, tuck them in shade and they can stay outside for about 2 hours.
Is it partly cloudy? Expose to no more than 2 hours of partly cloudy sunshine.
Is it cloudy or rainy? I let my plants stay out all day on cloudy days from day 1 under protection (row cover that cuts 30-40% of the light out).
****After the duration of full sun exposure, bring indoors. I don’t put mine under lights again once I start hardening off.
Evening: If temps will be warm enough, leave outside. This just makes the whole process easier on us.
Day 2
Is it sunny? If yes, limit full sunshine to no more than 90 minutes.
Is it partly cloudy? Limit to partly cloudy to no more than 3 hours.
Is it cloudy or rainy? Repeat Day 1 (stay out all day under cover).
****After the duration of full sun exposure, bring indoors. I don’t put mine under lights again once I start hardening off.
Evening: If temps will be warm enough, leave outside. This just makes the whole process easier on us.
Day 3
Is it sunny? If yes, limit full sunshine to no more than 3 hours.
Is it partly cloudy? Limit to partly cloudy to no more than 4 hours.
Is it cloudy or rainy? Repeat Day 1 (stay out all day under cover).
****After the duration of full sun exposure, bring indoors. I don’t put mine under lights again once I start hardening off.
Evening: If temps will be warm enough, leave outside. This just makes the whole process easier on us.
Day 4
Is it sunny? If yes, limit full sunshine to no more than 4 hours.
Is it partly cloudy? Limit to partly cloudy to no more than 5 hours.
Is it cloudy or rainy? Repeat Day 1 (stay out all day under cover).
****After the duration of full or part sun exposure, bring indoors. I don’t put mine under lights again once I start hardening off.
Evening: If temps will be warm enough, leave outside. This just makes the whole process easier on us.
Day 5
Is it sunny? If yes, limit full sunshine to no more than 5 hours.
Is it partly cloudy? Limit to partly cloudy to no more than 6 hours.
Is it cloudy or rainy? Repeat Day 1 (stay out all day under cover).
****After the duration of full or part sun exposure, bring indoors. I don’t put mine under lights again once I start hardening off.
Evening: If temps will be warm enough, leave outside. This just makes the whole process easier on us.
Before Day 6, I really lean on my row cover and hopeful cloud decks to make this process easy. Day 6 commences my first longer periods of direct and part sun.
Day 6
Is it sunny? If yes, limit full sunshine to no more than 6 hours.
Is it partly cloudy? Limit to partly cloudy to no more than 7 hours.
Is it cloudy or rainy? Leave outside no cover (perhaps under an eave if it’s really a downpour).
****After the duration of full or part sun exposure, bring indoors. I don’t put mine under lights again once I start hardening off.
Evening: If temps will be warm enough, leave outside. This just makes the whole process easier on us.
Day 7
Is it sunny? If yes, limit full sunshine to no more than 7 hours.
Is it partly cloudy? Limit to partly cloudy to no more than 8 hours.
Is it cloudy or rainy? Leave outside no cover (perhaps under an eave if it’s really a downpour).
****After the duration of full or part sun exposure, bring indoors or set under a picnic table or other deep shade. I don’t put mine under lights again once I start hardening off.
Evening: If temps will be warm enough, leave outside. This just makes the whole process easier on us.
Full sunshine I try to reserve for after the first week! I know this sounds crazy, but at this point I know they are almost fully hardened off, having had many days of protected sun. At this point, sunscald is almost a non-issue. Once I’m a week in, I’m more or less letting them stay outside all day and
Day 8
Is it sunny? If yes, limit full sunshine to no more than 8 hours.
Is it partly cloudy? Limit to partly cloudy to no more than 9 hours.
Is it cloudy or rainy? Leave outside no cover (perhaps under an eave if it’s really a downpour).
****After the duration of full or part sun exposure, bring indoors or set under a picnic table or other deep shade. I don’t put mine under lights again once I start hardening off.
Evening: If temps will be warm enough, leave outside. This just makes the whole process easier on us.
Day 9
Is it sunny? If yes, limit full sunshine to no more than 10 hours.
Is it partly cloudy? Leave outside no cover all day.
Is it cloudy or rainy? Leave outside no cover (perhaps under an eave if it’s really a downpour).
Evening: If temps will be warm enough, leave outside. This just makes the whole process easier on us.
Day 10
It’s transplanting day! I usually wait until the evening to do this to ease the transition. This gives them the night to acclimate to their new environs.
