Acclimating Your Seedlings to the Outdoors

Did you accidentally come home from the market with a tray of dainty seedlings? We know…they’re hard to resist. These tiny buds have spent their youth in a leisurely, climate-controlled and sterile environment. In this nursery or store setting, there is no sudden gust of wind or swing in temperature. Before these sproutlings can be planted outside, they’ll need a bit of a buffer. If you plant tomatoes early, they’ll be stunted their whole lives. You are the mediator, the advocate, the Head of Acclimation. This is your moment.

Without “hardening off” or acclimating a plant, it can get transplant shock from wind, sun, cold and/or frost. Wind can break its cell walls, while sun and frost are too intense for the plant to bear. How are we to know the best time to take the leap and put our plant friends outside? One way is to note the first and last frost dates for the year, and transfer the tender plants outside when it’s least likely to be frosting again. Another option is to base your gardening moves off of what the moon is doing. Regardless of which scheduling option you choose, it is essential to monitor the temperature of your soil. But first: frost dates or moon phases?

To utilize frost dates, check the growing zone for your area and count backwards from any estimated last frost dates (here is the Farmer’s Almanac frost calculator; just put your zip code in and press “search”). Bear in mind, these dates are calculated based on climate normals between the years 1981-2010, so it’s not 100% accurate. 

Alternatively, if the moon is pulling you toward it, just allow it. Here’s how gardening by the moon works: just as the moon’s gravitational pull makes tides rise and fall, it also affects the moisture of soil. During the full moon and new moon, seeds absorb more water because there is more moisture pulled to the soil’s surface. Filled with lunar enchantment, the seeds will germinate faster, and become more well-established in their roots. Here is a moon phase calendar for you to start calculating. In our opinion, this method is a bit safer to follow than the former, because it is tied to earth’s natural pulls. However, it doesn’t take your climate into account. We marry the two options; here’s our routine:

If the frost calculator says that May 6th is the last spring frost for your area, cross reference that with the moon calendar (let’s say the full moon is on May 11th). Around that time, check the ten day forecast, and then plan which day to begin hardening off. 

Lastly, the temperature of the soil! Is it primed to welcome and nourish your seedlings? All plants need a baseline soil temperature to ensure their survival. Using a soil thermometer, stick the thermometer as deep as it’s recommended for your plants to be placed. If the ground is hard, make a pilot hole with a screwdriver so that your thermometer doesn’t break. To double check the temp, take a reading both in the morning and in the late afternoon. Here is a resource for soil temperature monitoring.

A calm, cloudy day is the best setting to begin their journey to the outdoors. This is it; the start of plant acclimation. 

Days 1 + 2

Place your seedlings in a protected area of your property. We recommend leaving them in the pots they came in. Choose a space that is north facing, that isn’t in direct sunlight, and is shielded from wind. Leave your buds outside for 1-2 hours, for the first two days. 

Days 3 + 4 

During these two days, give them about 3-4 hours outside. If it starts to rain, it’s ok! Let them drink it up. As you gradually increase their time outside, move them to the south facing side of your house where the sun is a bit more intense. 

Days 5 + 6 + 7

Continue to help them gain strength in their new environment, adding an hour or two every other day. Carrying out this process could take up to ten days, depending on time of year and which plants are at hand. Seedlings that came in a non-compostable container can be transferred to the ground toward the end of the hardening off process, while seedlings in a compostable container can be put directly into the ground.

To make this process of hauling seedlings inside and outside easier, consider assembling them on a big tray, or putting them in a wagon to wheel in and out more efficiently. Also, as you’re going through this process, sprinkle eggshells into the soil that will be receiving the plants. Eggshells are rich in calcium and are any plant’s best friend, providing an enormous boost of nourishment year-round.

Watering Routine

During this chapter, water your plants once per day. Monitor moisture levels by sticking your finger about an inch into the soil. Cool and damp to the touch is perfect, while dry and crumbly means more water is needed. If you are observing yellowing leaves, you’re either over-watering or under-watering. 

If you want to challenge yourself by experimenting with the  micro-climates on your own property (for example, affecting temperature by composting, covering seedlings with a dome made out of a plastic milk jug with the top cut off, or planting your garden in a bale of hay), keep us posted on your successes. 

New growth brings hope. Cheers to that!

Until next thyme, 
My Thyme Gardens

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