06/08/2026
HARDENING OFF SEEDLINGS/PLANTS
Hardening off seedling and plants is a necessary part of gardening to ensure that plants will be able to adapt to life outside and thrive. Hardening off reduces the risk of transplant shock (which may result in slow or stunted growth), strengthens stems, promotes healthy root growth, increases sun tolerance, and decreases risk of disease.
LOCATION AND LIGHTING:
Choose a location that allows the seedling to get at least 4 to 6 hours of direct sunlight, but not the intense midday sun. Dappled shade during peak sun hours is best. Too much sunlight can cause scorching and discoloration of leaves, while insufficient light can result in weak stems and poor growth.
TEMPERATURE:
Areas that are prone to extreme temperature fluctuations should not be selected. A relatively stable temperature between 60°F and 75°F is ideal. Temperature fluctuations can be detrimental. If the temperature difference between indoors and outdoors is too drastic, it can shock the seedling. A 10-15°F difference per day is considered safe.
PROTECTION FROM WIND, RAIN, AND PESTS:
Wind protection is also crucial, so find a location that provides a bit of a windbreak such as a patio or somewhere surrounded by walls. Exposure to strong winds can cause stems to bend or even break and may cause the seedling to dry out. Water borne diseases or root rot may be caused from heavy rainfall. Seedlings can be susceptible to pests like aphids, whiteflies, and spider mites that can quickly infest the seedlings and cause severe damage. Consider using row covers or fine mesh screens to shield them from wind and debris. For pests, introduce beneficial insects, such as ladybugs or lacewings.
WATERING:
Continue to provide the seedling with the right amount of water. Be mindful that they may dry out more quickly during this process, so do not overwater or underwater. As a general rule water when the top 1-2 inches of soil feels dry. An estimate of how often to water your seedlings during the hardening-off process: is every 2-3 days for small seeds (e.g., lettuce, herbs) and every 4-5 days for larger seeds (e.g., tomatoes, peppers). It is still prudent to check for moisture by inserting your finger into the soil. If the soil feels moist, you may be able to wait to water.
NUTRIENTS:
Consider using a balanced fertilizer (e.g. 20-20-20-NPK) as this will provide essential nutrients without promoting vegetative growth. Be mindful not to overdo it.
References: Hardening Off Seedlings: A Step-by-Step Guide to Transplant Success - Plant Grower World and Bing Co-Pilot search results. Picture: susansinthegarden.com
