Starting seedlings indoors

If you are considering starting your own flower or vegetable seedlings indoors and transplanting them into the garden later, this article is for you. Some of you may have already tried it, but with poor results, mainly because of the spindly transplants that resulted.

Well, there is good news – sturdy, compact seedlings can be successfully grown indoors under artificial lamps. It’s a relatively inexpensive way to grow a wide variety of plants. Read on to see how. 

The natural light from a window is seldom enough for good, strong seedling growth. They will usually stretch and lean towards the light and will not produce sturdy plants.  Incandescent bulbs give off more heat and less light than fluorescent tubes and will not, by themselves, produce good transplants.

Grow your seedlings under fluorescent or LED lights. Some brands of lights are sold as “grow lights,” designed to provide light in specific ranges required by plants. Standard fixtures with two “cool white” fluorescent tubes per fixture also give plants adequate light and are inexpensive. A combination of cool white and natural daylight tubes provides good ideal light for plants.

Hang lights from chains to ease raising them as the plants grow. Keep lights no more than three inches above the tops of your seedlings: two inches is ideal. Remember-lack of light is the major cause of elongated, skinny stems. 

How many light fixtures should you use? The coverage of light you provide is critical. Make sure the entire surface area of the seedling tray is covered by intense light. A single fixture with one or two bulbs is not sufficient for a tray of seedlings which extends beyond the area directly below the bulbs. 

Those of you who have produced somewhat spindly seedlings indoors can most likely trace your frustration to a lack of light coverage. The more light the better!

Plants need 12 to 16 hours of light daily. Don’t leave the lights on continuously, as plants need a dark period each night to develop properly. A simple timer can be part of the set-up so lights are turned off and on automatically.

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 smaller your seeds, the finer the mix will need to be. 

The best germination temperature for most flower and vegetable seedlings is 70-80 degrees. Bottom heat can be very beneficial for this. Bottom heat can help to prevent damping-off, the death of tiny seedlings due to fungus pathogens at the surface of the potting mix. 

Electric propagation mats specifically for seed starting are available from many garden centers and online suppliers. Keep in mind, too, that the temperatures in the potting mix of indoor containers can be as much as five degrees lower than indoor air temperatures. I recommend that the soil temperature not be allowed to fall below 70 degrees or uneven germination or damping-off may become a problem.  

Keep the potting mix moist while the seeds are germinating. Water the surface gently with a spray bottle or mist nozzle from a water hose so you don’t wash the potting mix out of the containers or disturb the seeds. Be careful not to let the potting mix dry out from a lack of water. 

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.

Seedlings draw energy for germination from nutrients stored in the seed. They don’t need fertilizer until they have several sets of true leaves. Seedlings of this age will benefit from a weak general-purpose water-soluble fertilizer mixed at 1/4 strength. Fertilize once per week. Water as needed for the rest of the week with plain water.

Good luck with your spring seedlings!

Tim Lewis is a Georgia Green Industry Association Certified Plant Professional, gardening writer, and former Perry High School horticulture instructor. He can be reached at (478) 954-1507 or timlewis1@windstream.net.