Transplanting Seedlings Outside: How-To Guide - From Soil to Soul

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Transplanting Seedlings Outside: How-To Guide

by on May 5, 2021
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Your seedlings are ready to move out of your cozy home to the great outdoors. It’s one of the most exciting parts of gardening. After all your hard work, you want to make sure your plants succeed and don’t experience transplant shock or, arguably worse, get damaged by pests.

Below is our how-to guide for ensuring your seedlings succeed in their new home.

In this post, we cover:

When to Transplant for Your Grow Zone

Before you transplant your seedlings into your garden or raised bed, you need to know;

1. Your grow zone. This is key to not only transplanting, but having a successful garden all around.  The Canadian Plant Hardiness Zone Systems are based on many factors, including first and last frost dates and average amount of annual rainfall. In Canada, zones range from Zone 0 (North West Territories) all the way up to Zone 9 (Southern Gulf of British Columbia). The warmer the climate, the higher the zone. For my Zone 3b climate, I usually start transplanting in the greenhouse as early as March but wait until May to transplant seedlings directly into the garden. 

2. Your plant’s hardinessNot all seedlings should be transplanted at the same time. Some plants can tolerate light frost and cold temperatures, such as brassicas, spinach, Asian greens. Whereas other plants, like tomatoes and peppers, are tender annuals that must be planted after your last frost date. Enter your Canadian or American postal/zip code on The Farmer’s Almanac zone finder to find your projected last frost date for your exact location.

So, plan to transplant your seedlings when it’s appropriate for both your grow zone and for the type of plant you want to get in the ground.

Prior to transplanting, check your short and long-term weather forecast. It’s best to transplant when day time temperatures aren’t too hot that they’ll scorch plants, and when nighttime temperatures aren’t dipping too low that plants could freeze. Better yet, transplant the day before or day of a rainfall. Your seedlings will thrive after a good rain. Just be sure the forecast doesn’t have a big storm in the near future, which could wash away your seedlings.

Hardening Off Seedlings

Hardening off is somewhat of an art form. It requires patience and planning. It’s not necessarily a “fun” garden task (trust me), but it’s so key to success. Hardening off is the process where you gradually introduce your seedlings to the outdoors over a few weeks. Slow and steady are the golden rules here and will help your plants get stronger and more resiliant to disease and other damage throughout the season.

Why Harden Off Seedlings?

  • Exposes your plants gradually to outdoor temperatures, sunlight and wind.
  • Avoids transplant shock
  • Strengthens your plants and makes them more sturdy
  • Gives you “insurance” on your plants surviving
  • Gives your plants a head start on maturing, ideally providing you an earlier harvest

So, how do you start the hardening off process?

Well, you can gently start hardening off your seedlings as early as two weeks after they germinate. With this first initial introduction to hardening off, you will continue to keep your seedlings indoors but place a small fan near them to create a light wind. We use smally, plug-in fans that clip onto our shelves. We move the fans throughout the day so our seedlings get wind blown from different directions. This is your seedlings first introduction to what living outside will be like.

Then, we start hardening off seedlings outdoors at least two weeks before they are transplanted in the garden. To know exactly when to start hardening off seedlings outside, download our Free Planting Guide and begin two weeks before the transplant date for your zone.

2-Week Hardening Off Schedule:

Day 1-3: Keep seedlings outside for a few hours daily, but not in direct sunlight. I create a little shade cover with patio chairs, blankets, etc…Typically, I place my seedlings outside first thing in the morning and bring them in by early afternoon. This way they are not exposed to the sun and heat at the warmest time in the day. If day time temps are cooler than 10°C, I don’t bring seedlings outside.

Day 4-7:  Begin to gradually increase the daily hours your plants are outside for by one to two hours daily. By the end of the week, day seven, your seedlings should be outside for at least eight hours/day. 

Day 8-10: Begin monitoring your overnight lows. Wait until night time temps are 10°C or warmer and then leave your seedlings outside overnight. For hardy plants, like brassicas and greens, cooler overnight temps will not affect them. You can keep them outdoors even if temperatures dip as low as freezing. 

Day 11-14: Seedlings should be spending 24 hours outside at this point. You can transplant them at any point between day 11-14.

Preparing Your Soil

You’ve prepared your seedlings for transplanting, now it’s time to prepare your soil. Healthy soil is living soil, meaning you need to feed your soil continuously. Ensuring your soil is filled with nutrients will help your seedlings set down their roots.

Soil becomes depleated of nutrients after growing food all summer and then being covered in snow for the winter. You want to amend your soil both before transplanting as well as throughout the growing season.

In our organic Zone 3b garden, we amend our soil in three ways:

1. Cover soil with organic mulch, like straw and leaves. We mulch around the base of our plants during the summer to help retain water and surpress weeds. Then, we do another heavy mulch, covering the entire soil surface in the fall. Our mulch not only protects the soil from winter’s harsh elements, but it also breaks down in the Spring, adding organic matter to our soil.

2. Top dress plants with compost. Top dressing is the process of adding a thin layer of compost around the roots of your plants. This approach provides slow-release nutrients to your plants.

3. Water with a liquid, organic fertilizer. Add a liquid fertilizer, like Sea Magic, into your watering schedule every few weeks. The benefits of supplementing your plants with a liquid fertilizer are endless! It will help build resistance against disease, set deeper roots and increase blooms and fruit production on edible plants. 

To prepare soil for transplanting day, add organic compost to your garden beds or containers a few days to one week before you plant to transplant. I like to water the area where I’ll be transplanting a few times before hand too. This helps mix the compost into the top soil and begins slow releasing nutrients.

If your busy life gets away on you, you can also add compost the day you plant. One of the wonderful aspects of organic fertilizer is that it won’t burn or harm your plants like a synthetic fertilizer would. So, amending your soil the day of transplanting works great too!

Other ways to prepare your soil:

  • Pull out any weeds or plant remains from the season before. 
  • Use a garden rake to gently mix in mulch, compost and top soil.
  • Level out soil to ensure water is absorbed evenly throughout your garden bed.

Transplanting Tips

It’s time! You’re ready to put your seedlings in the ground.

Here are our top three tips for transplanting. These tips can be applied to any flowers, herbs or edible seedlings you plant.

Tip 1: Dig a hole about twice the depth and diameter of your seedling. There’s no “one size fits all” when it comes to digging a hole for transplanting. It is dependant on the size of your seedling. For example, smaller plants between three to six inches should be planted in a hole only a few inches larger than the root ball. If your plants have become leggy and stretched out, you can plant them a bit deeper by burying a portion of the stem.

Tip 2: Water heavy and gently break the roots. Deeply water your seedlings before transplanting so the roots are well hydrated. In years when it is hot and dry, I also flood my hole with water before putting in the transplant. This makes the soil quite mucky but will ensure your roots absorb water. Remove your seedling from its container and gently break apart the roots with your hands. This does not harm your plant. This is called teasing the roots, and it helps the roots spread deeper and in all directions.

Tip 3: Provide lots of space at first, then fill in after if needed. Overcrowding transplants (planting them too close together) is a recipe for disaster. It causes your plants to be more susceptible to disease and to compete for root space. When transplanting, I make sure I give my seedlings lots of extra space. Once they’ve caught and started to spread out, I fill in any empty spaces with short season crops, such as beets, turnips, radishes, lettuces. Remember, you can always add more after!

Here’s a quick look at spacing recommendations for various plants: 

  • Root Crops = a few inches apart, then thin more as the crop matures. Examples: Radishes, beets, carrots.
  • Small Plants = 10-15 inches apart, depending on the exact variety. Examples: Peppers, eggplant, kale.
  • Bushy Plants = 18-24 inches apart. Examples: Bush beans, cauliflower, broccoli, summer squash.
  • Vining Plants = 20-30 inches apart, plus add a support for the vines to climb up. Examples: Tomatoes, pole beans, cucumbers, winter squash.

Covering Seedlings to Protect Against Pests and Harsh Weather

Now that your seedlings are in the ground, you may want to consider providing them some additional protection. Here’s a few reasons why:

  • Creates more productive plants
  • Helps you harvest more long term, possibly even year-round
  • Reduces pest problems
  • Controls the environment your seedling is in, creating a micro-climate
  • Retains soil moisture

There’s many ways you can do this. You can decide whether your solution needs to be permenant, lasting all season long. Or, whether a quick DIY solution is sufficient. Covering plants is completely dependant on where your garden is located and what type of pressure your seedlings experience.

Some examples of pressures and solutions.

Pressure A: Your garden gets full sun all day and plants tend to wilt or burn.

Solution A: Cover for a few hours during the hottest part of the day with a mini hoop tunel with row cover.

Pressure B: Your garden gets eaten by deer.

Solution B: Cover your garden beds with a chicken wire or fine mesh netting.

Pressure C: You have a short growing season.

Solution C: Cover a raised bed with greenhouse poly to create a cold frame.

Pressure D: You see a frost in the forecast and have tender plants in the ground.

Solution D: Cover with a cloche or plastic container to create a mini greenhouse effect.

Start Planting

Happy planting! I hope these tips on transplanting success help your seedlings thrive this season. Leave a comment below if you enjoyed this post or have more questions.

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