If you grow from seed, you may be aware of their gentle nature. As a result many of us start our plants in indoor or controlled environments. While this procedure can help spark the life of these beautiful beings we are caring for, care must also but taken when transitioning them into outdoor, natural environments. This process is often referred to as harding off.

Today I wanted to share with everyone a little experiment I have done with my tomatoes, and hope to illustrate to importance of taking careful measures when transplanting.

The first photo is of a few seedlings I started inside, a windless environment. The plants sat in a windowsill facing south, getting moderates amount of indirect sunlight. The second photo is of tomato seedlings started on my roof. The plants have been shielded by the sides of the container, about 6 inches between the top of the soil and the top of the container; but as we understand the properties of aerodynamics this shielding occurred only to an extent. The container being directly on the roof also underwent constant sunlight. Again, minus the shade time when the sun is at lower angles.

Indoor Grown Seedlings

Outdoor Grown Seedlings

Both of these plants where grown from the same seeds and started at the same time. Notice the characteristics of the stems and leaves. The indoor grown is much more fragile, even upon sight.

What has occurred is that the outdoor grown plant has developed a thicker cuticle. The cuticle is a layer of waxy materials deposited by the outer, epidermal, cells that cover every bit of a plant. ₁ It’s purpose is for protection and to help the plant from drying out. As wind blows by a plant, moisture is lost at a faster rate. This outer layer acts to limit this.

The indoor grown plant also has wider, greener leaves. This is a reaction the plant has taken to comply with the amount of light received. The plan’s exposure to sunlight was limited, being faced beside a south facing wall. As a result of this limited sunlight more emphases was put into leaf production in order to make the most out of what sunlight was bleeding through the pane of glass.

In conclusion of this little experiment, we see that the differences in environment inhibit different plant characteristics. Knowing this we must also understand that a plant has the ability to adapt to changing environmental conditions, but time is required to do so. To compensate for this time we must limit the degree of conditions that will harm a yet to adapt plant while introducing the plant to these conditions in order to encourage the adaptation.

Hardening Off

Things you can do to ensure a healthy transition from indoor to outdoor environments:

1. Harden off gradually over a week+ day period.
2. Water less frequently progressively, prior to transplanting but do not allow seedlings to wilt. Avoid fertilizing.
3. In a mild sun, start introducing 2-3 hours of direct sun a day, Increasing exposure a few additional hours at a time.
4. Protect seedlings from strong sun, wind, hard rain once transplanted.
5. Keep an eye on the weather and listen to the low temperature prediction, and know the relative hardiness of your various plants.
6. Gradually increase exposure varying temperates than started in.
7. Root-prune plants in flats a week before setting out. Use a sharp knife and cut down to the bottom of the flat between the plants. Water thoroughly.
8. Use a weak fertilizer solution after transplanting to encourage growth and to help avoid transplant shock. ₂

Notes

 1. Watson. Thomas T. “Bracing Up: Hardening Off Transplants.” University of Arizona College of

              Agriculture.

2.  Kennell Holly S.”Hardening off Transplants.” Washington State University, WSU Extension Agent, King County.