Time to Harden Off the Tomato Plants
The tomato seedlings at the 2nd Street Chicken Ranch have enjoyed all the comforts of home and have been growing nicely in a constant 67 degree room filled with filtered sunlight. Pampered for sure. However it’s time to take off the (garden) gloves and stop the babying. Sometimes you have to be tough…and your tomato plants have to be even tougher to survive being transplanted into the ground. That’s where hardening off pays off. If the tomato seedlings aren’t property hardened off, come planting time they would parish almost immediately from the sun, the wind and the rain.
It’s time to harden off when three to five sets of true leaves appear.
When your tomato seedlings have three to five sets of true leaves, it’s time to get them ready to face the world outside the house (or greenhouse).
The Right Conditions to Harden Off Plants
The process of hardening off gives plants a chance to slowly adapt to the outdoor environment in which they will grow, and it promotes stronger plants. Tomatoes are warm-weather plants and are very fragile at this stage of growth. Hardening off should be done on clear or overcast days (no rain), when daytime temperatures are at a minimum of mid-50 degrees, with little to no wind. Granted, those conditions can sometimes be difficult to come by in April!
The process should be conducted slowly over a week to ten days. The rule of thumb for hardening off tomato plants is one hour outside on day one, two hours outside on day two, and so on until the plants are outside for the entire day. Given weather conditions, this process can often take a week or more to complete.
Keep young plants out of direct sunlight to avoid sunburn.
On the first day place plants close to the house (a shady east or north facing side is best) or in an area protected from wind. The plants are extremely susceptible to sunburn, so keep them out of direct sunlight for the first three to five days. As they adapt you can place them in filtered sunlight.
Check your plants daily for sunburn (leaves will turn white), windburn and water needs. The plants will dry out much quicker outside than indoors, so adjust your watering accordingly.
Your plants may start to look a bit ragged; even a gentle breeze can take its toll, but your plants will recover and begin to get stronger. Note the word “breeze” — if it is a windy day, it’s probably best to keep the plants inside or move them to an unheated garage. For leggy plants, a bamboo stick or chopstick support may be needed to keep them upright.
After a week or so, you will notice the plants “greening-up” (turning a darker green), and that their stems are becoming much stockier. When your plants are spending their days outside and overnight temperatures are consistently above 50 degrees, they will be ready to plant in the garden or pots. If it is still too early to plant (before the last average day of frost or still too cold at night), move your plants into a garage or covered bed at night.
Do not leave your plants outside overnight until the night time temperatures are above 50 degrees.
If you purchase tomato plants from a commercial grower, it’s a good idea to ask if the plants have been hardened off. If that information is not available, assume that the plants have not been hardened and follow the steps above.
Looking for locally grown (and hardened off) Heirloom Tomato Plants? We have 25 different varieties for sale. Plants will be ready around May 1st from our CdA garden or at the Wednesday Kootenai County Farmers Market in downtown Coeur d’Alene.
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