Your seedlings look happy and healthy because you started with seeds sown indoors for vegetables, herbs, and/or flowers. Please, they’re not ready for that yet. The most important step in successfully growing plants indoors, often overlooked by new gardeners, is gradual acclimatization to the outdoor environment. This is a process called “hardening”. You have to pay close attention to the fairly drastic changes in conditions your seedlings are about to experience.
Let’s look at it from a plant’s perspective. Plants grow in a comfortable and consistent environment with constant temperatures, regular watering, bright (but not too intense) light, and no wind. That’s all about to change. If you want your seedlings to thrive in your garden, you’ll need to gradually acclimate them to the capricious outdoor conditions.
Seedlings must develop tougher protective cuticles and sturdy stems to adapt to natural fluctuations in temperature, light, water and air movement without damage. This takes some time and patience. Skipping this critical step can leave tender young plants in shock and irreversible.
1. Know when to harden seedlings.
The best time to start moving seedlings from indoors to outdoors varies slightly from crop to crop. Cold season vegetables such as cabbage and broccoli, as well as hardy annuals and herbs such as calendula, marigolds and pansies, can begin the curing process when nighttime temperatures reach 45°F. For warm season crops (tomatoes, peppers, cucumbers, etc.) and softer herbs and flowers, wait until nighttime temperatures are in the high 50s.
2. Gradually introduce seedlings outdoors.
When the temperature is right, take the seedlings outside for a few hours on the first day and bring them in at night. The next day he increases his outdoor time by an hour or he increases it by two hours and continues this way for two weeks. Pay attention to the appearance of your seedlings. If they appear stressed, slow down their outdoor exposure. Once they can tolerate being outdoors all day, take them out overnight.
3. Choose a protected location.
Spots of dappled shade help the seedlings acclimate to more intense light from the sun. Don’t. This can lead to charred leaves, stunted growth, and even death. Wind can also cause serious damage, so place the seedlings in an area protected from strong winds. Boxes with sides that deflect strong air currents work well. Cold frames are a great tool for hardening seedlings, as the sides protect the plants from the wind and the translucent furrow cover can be used to block direct sunlight.
4. Water the seedlings.
Check the seedlings regularly. If it’s sunny and warm, check at least twice a day. Keep them moist but not oversaturate and make sure the pots have drainage holes. And heavy rain can break fragile stems. If heavy storms are expected, it’s best to bring the plant indoors, in a garage, or on a covered porch.
5. Slowly increase the time of exposure to garden conditions.
As your young plants get used to being outdoors, they will develop tougher cuticles that provide much better protection from the elements. I like to move potted saplings into the growing garden and leave them for a few days to let them acclimate to the place before transplanting them into the ground or planters.
6. Transplant on a mild overcast day.
Transplanting when bright sunlight is softened by clouds reduces stress on young plants. . well. If the wind picks up, use a plant cover or some sort of baffle to protect them. Large inverted plastic pots also provide temporary shelter.
7. Watch the weather.
Watch for sudden drops in temperature and heavy rain during the first few weeks the plant is above ground. Plant protection caps, upside-down pots, or floating row covers can help survive late-season frost and storm damage.
The indoor-to-garden transition process can seem rather daunting, but it is very important. Failure to allow seedlings time to acclimate to the outdoor environment will lead to serious disappointment. Plants may become stunted or even die. I already spend a lot of time and energy taking care of my seedlings indoors. Gradual hardening of seedlings is just the next stage in this process. After that, you and your plants are ready to be transplanted into your garden.