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News from the Edible Demo Garden

October 2021: Seedling Transplanting Tips

Zoe Schaeffer, Unsplash
Zoe Schaeffer, Unsplash
At the Edible Demonstration Garden this month, we have been following best practices for seeding our winter garden plants in the greenhouse. These practices were outlined in last month’s article.  This month, we will begin moving some of these seedlings into the garden.  Right now they are in the greenhouse with temperature controls and fans that keep the air moving.  Home gardeners do not usually have the benefit of a greenhouse. Even so, if seedlings are started in your home, it is still a much kinder environment than exists outside.   So what is the best procedure for moving delicate seedlings into your garden?

When is a seedling ready to move?

The most common problem with transplanting is timing.  Many gardeners, including our team, make the mistake of waiting too long. A good rule of thumb is that the seedling should have at least three to four true leaves in addition to the seed leaves that appear first. The height of the seedling is not as important as the number of leaves it has.  An ideal seedling would be as wide as it is tall.  So how do we toughen up that soft, succulent type of growth into a firmer, harder type?  This process is called ‘hardening off’.

Take the Time for Hardening Off

Your seedlings need a transition time to the harsher outside conditions.  If you do not provide this, a severe, long-term check in growth can occur.  The hardening process will take at the very least seven days or up to two weeks, so this requires patience.  Remember that you’re looking for the plant to lose those soft stems and harden up.  So observe your plants closely. 

Hardening Off Process

As you transition your seedlings to the outside, keep in mind the two elements that will have the most impact on them:  wind and sun.  A hot, windy day would not be the day to start the move.  For the first excursion, pick a temperate day with no wind and even then, put your plants in a protected area in the shade.  You might leave them out for only a few hours.  After that, increase the exposure time each day, moving eventually to dappled morning sunlight, and then gradually to full morning sunlight.  Placing plants in full afternoon sun will be done toward the end of this process, as well as leaving them out overnight, but only when temperatures do not fall below 50°F.  Reducing water frequency to slow growth during hardening is advised.     


Transplanting Seedlings into the Garden

Like ‘hardening off’, choose your day and time carefully.  An ideal time would be the late afternoon or evening of an overcast day with little or no wind.  The worst day would be during a lengthy heat spell with lots of wind. 

Water your seedlings well before transplanting.  Then, dig a hole with the same depth at which the seedling is growing and a bit wider.  (Tomatoes, broccoli, cabbage, and cauliflower should be set deeper than they are growing.)  Mix in compost or a starter fertilizer at the bottom of the hole.  When removing the seedling from its container, treat the roots gently, trying not to tear them.  Also, if possible, handle the plant by its leaves rather than the stem.  After firming the soil around the plants, water gently including the leaves.  If there is concern about the effect of intense afternoon sun, you can choose to shade your seedlings by placing a board or piece of cardboard on the southwest side of the plants for a couple of days. 

Finally, the plants will likely experience little or no growth for up to several weeks, but do not get discouraged.  After that, the seedlings will have made themselves at home with roots that can support growth and your plants will begin to thrive. 

Congratulate yourself on the careful fostering of your little seedlings, and celebrate when they give back to you the abundance of their fruiting.