Seedlings indoors

Many of you have probably considered starting your own seedlings indoors and transplanting them into the garden later. Some of you have already tried it, but with only marginal results-mainly because of the spindly transplants that resulted. Well, there is good news — you can get a jump on spring, for seedlings can be successfully grown indoors under fluorescent lamps. Let’s see how.

You probably recall from high school biology that plants carry on photosynthesis, a complicated process in which plants take chlorophyll, light, carbon dioxide from the air, and water from the soil and make glucose, the plant’s food. The rate at which plants grow depends on three things related to light: (1) the kind of light (its color or wavelength), (2) light intensity (how bright the light is), and (3) its duration (how long the light is available to the plant).

Fluorescent lights are good choices for helping us meet our seedlings’ light requirement. There are many types of fluorescent lamps available to gardeners- Daylight, Cool White, Warm White, Natural, Wide Spectrum, and Gro-Lux. Of these, the Cool White and Warm White, used together, are excellent. Cool White bulbs emit mostly blue wavelength light. Blue light encourages slow, compact plant growth. Warm white bulbs, on the other hand, give off red rays which encourage taller, faster growth. When combined in a two-light fixture, they provide a low-cost, nicely balanced, long-lasting, efficient light. Using Daylight and Natural lamps together will also work, as will using either Gro-Lux or Wide Spectrum alone, though they may be more expensive than Cool White and Warm White bulbs.

What about the intensity, or brightness, of the light? Light intensity is a function of distance from the light source. Most seedlings will flourish with the lamps hanging about 8 to 9 inches above the tops of the plants. Putting the light farther away than 12 inches from the plants is not recommended. Center the seedlings directly under the light fixture.

Once you’ve selected a lamp and set it up for the right intensity, you must provide the correct duration of light for your plants. Plants should receive between 12 and 16 hours of light per day. Fewer than 12 hours will cause new leaves to develop slowly, and the plants will not grow well. Providing more than 16 hours will likely interfere with the plants’ natural growth processes, turning them pale and maybe even killing them. An inexpensive electric timer is a good investment to help you with this.

The best medium for seed germination is a sterile commercial soilless mix containing some combination of finely ground peat moss, perlite, and/or vermiculite with a pH of between 6.0 and 6.5. These mixes also contain a very small amount of fertilizer, or starter nutrient charge, as they are called. Common trade names are Jiffy-Mix, Redi-Earth, Terra-Lite, Fafard, and others.

The best germination temperature for most flower and vegetable seedlings is 70-80 degrees. Placing your setup near a stove or furnace or providing bottom heat to the flats with a heating cable will accomplish this. The soil temperature should not be allowed to fall below 65 degrees or uneven germination or seedling diseases may become a problem.

Once the seeds have germinated, the seedlings should be given a temperature of 70-80 degrees during the day and 60-65 degrees at night. This daytime temperature allows the plants to maintain a high rate of photosynthesis for food production. During the night, however, the plants’ food production ceases and its other physiological processes speed up, and food produced during the day is consumed. Lowering the night temperature ensures steady, even plant growth which makes for strong, compact plants for the garden.

Air circulation is another vital component to good plant growth. You may consider running a room fan for this, since it makes more carbon dioxide available and decreases the incidence of disease.

Most seedlings are ready to be transplanted when they have grown their first set of true leaves. A true leaf is one which looks like a mature plant leaf. They will usually appear two to four weeks after germination, depending on the plant being grown.

Good luck with your spring seedlings. Let me know if I can help.

Tim Lewis is a Georgia Green Industry Association Certified Plant Professional, gardening writer, former Perry High School horticulture instructor, and former horticulturalist at Henderson Village and Houston Springs. He and his wife, Susan, own and operate Lewis Farms Nursery located on Hwy 26 two miles east of Elko, where he was born and raised. He can be reached at (478)954-1507, timlewis1@windstream.net, or at LewisFarmsNursery.com.

HHJ News