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The passionate Gardner for April 5, 2012

Once germinated, your flower seedlings no longer need high temperatures and humidity and do best at 60° to 65°F. If you have plastic over your seedlings, remove it as soon as green shoots emerge. High humidity and heat can encourage damping-off, a fungal disease that can kill the seedlings overnight.
Careful watering is crucial at this time. Too much water applied too fast can drown the seedlings. At this stage I use a spray bottle with a fine mist or the finest setting on a hose sprayer. If my seedling tray has dried out so that misting does not do the job, I place my tray of cell-packs into a basin of water to let the moisture soak up from the bottom soil.
Seedlings need 12 to 16 hours of light each day, which may seem excessive, but low rays of the winter sun and artificial lights are not as intense as summer sun. Lamp timers will help in this chore of keeping the seedlings basking in a regular light schedule. Do not place seedlings in direct sun because this will burn them.
The first set of two leaves that emerged are the cotyledons, which store food for the emerging seedling. When the true leaves appear, the cotyledons drop off. Now the true leaves begin photosynthesis and it is time for you to do your part to ensure robust plants by thinning and fertilizing.
Although some gardeners plant their seeds in one large flat and then transplant them into larger pots, I plant my seeds, at a rate of two to three seeds, into cell packs, so that after thinning, each plant will have its own “territory.” When your seedlings have four true leaves, thinning is essential because if a seedling cannot have room to spread out, it will be spindly and useless in the garden. Sometimes you can pluck out seedlings and transplant them, but the drawback is that you might disturb the roots of the seedlings. If the roots from two or more seedlings have grown together, cut the unwanted plants off at soil level.
The major macro-nutrients in plant fertilizers are nitrogen, phosphorus, and potassium, the letters N-P-K you see on fertilizer bags. Additionally, plants need micro-nutrients such as calcium, sulfur, magnesium, boron, and others.
I recommend a balanced but slightly elevated phosphorus fertilizer, such as a 6-12-6, and that the fertilizer package also state that it contains all essential trace elements. Ideally, look for an organic blend that might include fish, feather, and alfalfa meal, mined potassium sulfate, phosphate, seaweed extract, and beneficial soil microbes. Because specific organic fertilizers are difficult to find locally, you might have to search the Internet for what you want.
Dilute application of the fertilizer is critical. Most fertilizers are dry and mixed with water at a rate of 1 tablespoon per one gallon of warm water. Read the fertilizer package carefully and err on the side of a weak mix instead of a stronger mix, which could burn and kill the tender seedlings. Make sure the fertilizer is totally dissolved or use a liquid, diluted fertilizer. Never apply dry granules to seedlings. You can apply diluted fertilizer weekly. Be very careful not to over-water and over-fertilize your plants. Strong, healthy plants need some stress to be compact and ready for the garden.