It is that time of the year when the soil is warming up and people are starting to put in their garden starter plugs that they grew indoors. Starting plants indoors is a great way to get a “head start” on things and be safe from some late frosts that occur in April and May. When you are transplanting some of these plants, be sure to check the frost tolerance and make sure you put them out during the proper times.
Besides the frost, plants have to acclimate or “harden” from indoor conditions to outdoor conditions. When a plant grows indoors the light conditions can be as much as 40 times less intense than the full sun, and exposure time can be less than half of what it will be outside. Plants will generally grow thicker leaves and produce more chlorophyll to make better usage of the light energy provided to the plant when they are grown in low light conditions (indoors). This is actually one reason why lettuce is grown in partial shade.
(Plant Physiology 3rd ed.)
Taking this idea a bit deeper (down to the roots); it is important to remember that the water and nutrient uptake is essentially all done through very fine and tender root hairs. When a plant is moved many of these hairs are damaged and water uptake can become insufficient for the plant’s needs.
So let’s combine the problems now: A plant is moved to 12 times the sun, with increased chlorophyll and 2 times the light exposure that it is used to. On top of that the plant cannot get the water to support the increased photosynthesis demand in that direct sunlight. That could set the plant back, and all the sudden that “head start” might not be so advantages anymore.
Some tips from OSU Extension:
- Slowly transition the plant from indoors to outdoors by bringing it out for a few hours at a time without damaging the root hairs during the move (keep it in the original container).
- Don’t put out frost sensitive plants too early.
- Wait for the soil temperatures to warm up nicely (60 degrees or greater).
- When transplanting the starter plant, don’t let it get too big and don’t shake off too much soil from the root mass (root hair damage).
- Be sure to actively water the plant during the first week especially. This will compensate for the decreased water uptake ability of the plant.
- If you are utilizing weed control, make sure the pesticide doesn’t have a long residual period (refer to the label).
These tips will work for both gardening and landscaping; so when you buy a plant from a nursery, ask about the growing conditions. Things like: “Has the plant been growing indoors or outside?” And “How long has it been out and how much sun is it getting here?”