Harden-off transplants before placing in the garden

Published 12:00 am Saturday, March 24, 2012

All transplants will need to be hardened-off before planting in the garden. Many people plant transplants directly in the garden immediately after purchasing them, putting them directly in the sun and wind. They then wonder why the transplants dry up and die. If the transplants are not adjusted to the sun and wind, they will dry out and die.

Young transplants that were grown either indoors or in a greenhouse will need a period to adjust to the outdoor conditions before being planted in the garden. When purchased, most transplants are not ready to be put in the full sun and wind.  After all of the tender care given to the plants by the growers and sellers, the plants will need time to adjust to the harsh outdoor conditions. The process of slowly adjusting the plant to the outside conditions is called the hardening- off process. The hardening-off process gradually exposes the tender plants to the wind, sun and rain. This process toughens up the plants by thickening the cuticle on the leaves so the leaves lose less water. It also hardens the stem of the plant making it stronger and tougher. The process of hardening-off the transplants may take several days or even several weeks depending on the weather and the type of the plant. Some plants may be placed outside earlier than 1-2 weeks, but you must check the plant to make sure that it can handle the outside conditions. Possibly, shade barriers may need to be put up to protect the plants from the full sun.

Wind, sun and rain can wreak havoc on delicate seedlings, so you need to toughen them up and harden them off. The idea is to expose the plants to the elements gradually. This means to expose the transplants to the outside conditions slowly, over the course of six to 14 days, depending on time, temperature and the strength and toughness of the transplants.

Below is a schedule that may be followed to properly harden-off transplants. Remember the type of transplant, the amount of sun it receives and the outside weather conditions will affect the amount of time that it takes to harden-off the transplants.  

On day one make sure the transplants have been watered. Place the transplants outside in a protected area out of direct sun and wind for about 3-4 hours. Expose them to the sun for only 2-3 hours, but check them to make sure that they do not wilt too much.

From day two through day five, increase the time the transplants

are exposed to the sun, while keeping the plants protected from the cold and wind. Place the transplants in the morning sun for only about

 3-4 hours each day. Plants may also be placed in the afternoon sun for several hours if they can stand

the heat. Do not place plants in

the direct sun during midday. At

the same time, gradually reduce

the amount of water given to the transplants. Do not allow the transplants to wilt and dry out, but only water them lightly if they are

wilting. If they are wilting badly when placed in the direct sunlight, remove them from the direct sunlight, and place them in a shaded area, and give the transplants a little water. Do not fertilize the transplants until they are completely hardened off.   

During days six to 10, lengthen the time your plants are outside in the sun, until they can stay out all day, even during the midday hours. The plants may wilt a little during the day, but they will pop up during the night. You may still need to protect your plants even after they are

hardened-off in the event of high winds, sudden downpours or cold temperatures. Spring vegetable transplants started early will need to be protected in the event of a frost. A frost can damage the plants when the temperatures reach around 40 degrees Fahrenheit or lower and there is little or no wind. Use sheets, blankets, buckets, plastic jugs or plastic to protect the transplants from a frost. Be sure to remove the protection materials in the morning when the sun rises or the sun will heat up the covered plants and smother them.

After noticing that the plants can stay out in the sun all day, plant them in the garden or plant them in a container. A five-gallon bucket with holes in the bottom for drainage will do if you cannot plant the plants in the ground. If you

want to plant the plants in a bucket, you can purchase some potting

soil and mix it with some regular soil and sand, equal parts. Make sure you put the soil all the way to the top of the container. Make sure to water the plants thoroughly after planting. You can start adding

some fertilizer to their water after they are hardened-off and planted in the ground or in a large container. You may want to purchase a slow release fertilizer if you plan to

grow the plants in containers and if you are not using a liquid fertilizer. For plants in the ground garden follow the recommended fertilizer rates in the Vegetable Planting Guide.  

Plants should be watered in the early morning hours every day or two, depending on how well they can stand up to the sun. As the plants get older they may need to be watered every 3-4 days if they do not receive rain. The plants can also be watered in the evening, but allow enough time for the ground to dry before dark.  

Remember, newly purchased transplants will have to be hardened-off before they are placed in the garden. If not hardened off properly, plants will wilt and dry up. For more information on growing plants, the Vegetable Planting Guide is available from the Parish LSU Ag Center Office.  Information may also be found at the LSU Ag Center’s website at lsuagcenter.com.

If you have any questions, please contact your local LSU Ag Center County Agent. You can contact David Pichon, County Agent-St. John Parish at 985-497-3261 or by email at dpichon@agctr.lsu.edu.