How to Prepare Seedlings for Spring Planting

The weather’s warming up and spring is officially here. That means it’s time to prepare our seedlings for spring planting. But what exactly does this entail? New gardener’s might think that seedlings can be transferred straight to their outdoor gardens, but this isn’t exactly the case. In fact, there are two crucial steps that come before planting: thinning and hardening-off. Here, we’re going to walk you through how to thin seedlings and how to harden-off seedlings. 

Thinning Seedlings

What does it mean to thin a seedling?

Basically, to thin your seedlings means to weed out the weak. It’s almost like combing your hair; the dead strands, the weakest strands, are the ones that become tangled in the brush, leaving a healthy head of hair.

With your seedlings, you’ll want to remove the weakest ones and keep the healthiest ones. This is to prevent plant and seedling diseases, as overcrowding obstructs air circulation and encourages bacterial growth. In addition, plant-to-plant contact encourages the spread of disease (think social distancing!). 

So here’s how to do it. 

How to Thin Seedlings Correctly  

After you’ve planted your seeds and they’ve begun to sprout and have two sets of true leaves, it’s time to thin them. Thinning varies for different plants, so be sure to do some research about the specific plant you’re growing. 

If you’re growing something with delicate roots, such as beans, melons, or squash, thin them as soon as possible. 

Before thinning your seedlings, make sure the soil is damp first. This will help ease them out of the soil. 

You can thin your seedlings in one of a few different ways:

  • One way is to take a pair of scissors and snip the seedlings at the soil line. This is a good way to ensure you don’t damage any of the surrounding seedlings.
  • Another more laborious way is to weed them out with your fingers. This also ensures you don’t damage surrounding seedlings, but it is time-consuming.
  • A third way is to take a small gardener’s rake and rake out any of the unwanted seedlings. We don’t encourage this method, as it can damage the surrounding plants. 

After thinning the seedlings, you should water and fertilize them to promote growth. Once you have a healthy batch of seedlings, it’s time to begin the next step before planting: hardening-off. 

Hardening-off Seedlings

Knowing how to harden-off seedlings is essential because it prepares seedlings for planting. Your seedlings spent the beginning of their lives coddled under a warm and caring hand. They began in a temperature-controlled environment to ensure optimal growth, but they’re about to be planted in a harsh and unpredictable environment. Thus, you must prepare them. 

First-time gardeners often wonder why their seedlings didn’t make it when they did everything right. But the fact of the matter is that without the hardening-off process, many seedlings won’t make it. The sun and wind are too harsh for their fragile leaves and stems. Rain and hail (and anything else–since 2020 has seen an unpredictable hodgepodge of weather patterns so far) can crush your seedlings as well. 

So how and when do we harden our seedlings? 

How to Harden-off Seedlings 

Now is the time. 

Gardeners should begin the hardening-off process once temperatures reach 50 degrees and consistently stay there. The process will take seven to ten days, so begin about a week before you plan to plant your garden. 

Begin the process indoors. Take the plastic cover off the seed tray to introduce seedlings to an unprotected environment. You’ll want to introduce the seedlings to outdoor conditions, such as wind, in a controlled environment. Get an oscillating fan and run it at intervals so your seedlings can strengthen their stems. 

Once this is complete, take them outside and follow these steps to harden-off seedlings: 

  • Keep seedlings in their containers and place them in a shaded area where animals won’t bother them. A porch is the best place to put them because you don’t want to expose them to sun, wind, or rain just yet. If you see a storm in the weather forecast, take them back inside.
  • You’ll only want to leave them outside for a few hours every day. Leave them out for a few hours and then bring them back inside and place them under their grow lights again.
  • After three days, you can introduce your seedlings to sunlight. Place them in a non-shaded place during sunrise or sunset–never during the day when the sun is at its brightest and hottest.
  • Once you reach the middle of the ten-day process, you can begin to extend the amount of time your seedlings are outside. Keep them out an hour or two longer and expose them to the elements. Light rain showers or gentle breezes are fine, but if you decide to expose them to rain, remove the bottom tray first so they don’t drown.
  • Near the end of the process, leave them out at night–but only if the weather is above 50 degrees. Ensure they are in a safe and sheltered place, such as the porch.
  • The last step is to leave them out for a full 24 hours. Do this two or three times.

Once your seedlings have been hardened-off, you can plant them in your garden and they’ll have a much better chance of survival. 

Thinning and hardening-off your seedlings can be a laborious process, but dedicated gardeners know it is the best way to ensure a bountiful harvest. And remember: if you want your plants to grow healthy and have a vibrant hue, invest in a good nitrate fertilizer. xVital, our 100% eco-friendly fertilizer, is the best option for invested gardeners. Our fertilizer contains no salts or chemicals, which means it’s better for your plants and soil.  And because any leftover nitrate evaporates after plants have had their fill, it does not contribute to runoff or nitrous oxide pollution. Learn more here.


How to Harden Off Seedlings Before Transplanting