Complete Guide to Hardening-Off Your Seedlings




A Complete Guide to Hardening-Off Your Seedlings

Beginning seedlings indoors is a great way to get a head start on growing your own vegetables early in the season. The right soil temperature is important for seed germination, so when temperatures may still be too cold to direct seed, you can get them started in a protected environment such as a greenhouse or inside your home. This will help to ensure that your crops have the best opportunity to grow and produce to their full potential.

Starting seeds indoors also prevents wildlife from harvesting your seeds for their dinner and provides more direct seedling management.

An important element to remember when starting seeds indoors is to take time to harden them off before transplanting them into your garden.

Never hardened-off seedlings before? No problem! Read on to learn more about how to do it and why it is important.

Why Should I Harden-Off Seedlings?

Think of indoor-grown seedlings as tender little baby plants that have enjoyed a posh, comfortable and nurturing lifestyle indoors or in your greenhouse, that now need to be strengthened to the elements before they take up permanent residence in the big world outside.

Gradually adjusting seedlings to the outside world so they can thrive in it full-time is called “hardening-off” and is recommended so when transplanted they eliminate transplant shock and setbacks.

Seedlings grown indoors that are planted outside without sufficient hardening-off are prone to sunburn, wind damage, inability to uptake moisture and nutrients, and succumbing to the cold. They are not able to adequately adapt to their environment like a seed that is direct sown into your garden.

It is important to keep an eye on the weather forecast to decide when to start hardening off your seedlings before they are permanently planted outside. Be sure the soil temperatures are at or close to the recommendation for that crop. Cold temperatures can cause damage to the cell walls, halt growth and kill the plant.

Do All Seedlings Need to be Hardened-Off?

The general rule of thumb is that if you are going to start your seeds indoors, you should harden them off before transplanting them outside in your garden, regardless of type.

While some heartier plants, especially the brassica family of cabbages, kales, broccoli, and also lettuces will probably survive if you plant before hardening them off or forget to bring them inside for the night, but other more tender varieties such as peppers, tomatoes, cucumbers, and squashes could die, especially if temperatures were to dip into the 30°F range. Nighttime temperatures should consistently be above the 40°F, preferably 45° to 50°F range, when you begin the hardening-off and transplanting process.

How Do I Harden-Off Seedlings?

Hardening-off seedlings is relatively easy to do. During the day, set your plants outside, preferably on a mild and partly sunny day and let them get used to being outside. Place them in a shady area so they do not get too much sun exposure, which can cause the leaves to burn and the soil in your starter pots to dry out too quickly.

Seedlings should be hardened off for approximately 7-10 days before being transplanted to your garden full-time. You can refer to the Old Farmer’s Almanac to learn more about frost dates and temperature assessments for your area. Start out by leaving them outside for 2-4 hours for the first couple of days, and then gradually lengthen the time so that they spend 8-10 hours per day outside closer to the transplant date you have chosen. Bring them back inside at the end of the day so they can spend the night in their warm and cozy home. On the last day or so you can leave them out all night in a covered area.

Tips for Transplanting Your Seedlings

Once you have successfully hardened-off your plants and are ready to transplant them into your garden, keep the following tips in mind:

  1. Try to transplant seedlings on a cloudy day so they can adapt to their new home before basking in the warm glow of the sun.

  2. Plant your seedlings in nutrient rich soil so that they have plenty of ingredients in the “pantry” that they need to grow into robust vegetable bearing warriors.

  3. Check on your seedlings at least once per day after transplanting to ensure they are thriving in their new environment. Attend to their needs as necessary.

  4. Slugs love tender new leaves so start out be using Sluggo to discourage slimy predators.

  5. Insects can also be attracted to seedlings! You can deter them with an organic insecticidal soap spray, which is safe for plants and humans.

  6. Be careful not to damage the tender roots while removing seedlings from their starter pots. Keep as much soil with the roots as possible.

  7. Sprinkle a small amount of mycorrhizae on the roots as you plant your seedlings into the garden as this beneficial fungus will help your plants grow new roots and take in nutrients that are vital to their growth.

Avoid shocking your seedlings into an untimely death – remember to harden them off before planting them into your garden. Plants that have the opportunity to get used to living in their new home ahead of time will be strong and brave enough to thrive in whatever weather elements Mother Nature throws their way.

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