What is happening to my Seedlings?
Hey there! So I've recently gotten into gardening because it caught my interest. I bought a small greenhouse to work with at home and have a grow light LED attached to the top of it. I've been feeding my Seedlings once a week ever since they started to grow a good pair of true leaves to me. For this I diluted the liquid plant food to 1/4th of the recommended ratio to start building slowly towards the end ratio. With a measurement tool I measure the soil every day to check if it's moist enough. Unfortunately I noticed some yellow/brown -ish spots occur on my tallest seedlings (tomatoes). I have no idea what it could exactly be. Also some parts of the leaves took on a faded color, almost like it was bleaching I hope anyone would be able to help me out! Thanks a lot in advance -Ray
Certified GKH Gardening Expert
It appears to be a combination of nutrient burn and possibly the wrong spectrum of light/lacking certain spectra.
Many LED's will only contain red/blue diodes, with a few cheaper panels putting a few Whites in there on occasion. For a plant to be happy, these LED's will need to be, at least, a 9 band spectrum. 12 band spectrum will include infrared and ultraviolet which will help keep away bacteria and fungal infections.
Turning to a Ceramic Metal Halide fixture can grant you 4 feet by 4 feet of seedling space, while running at 315 watts. Alternatively, if you still wish to use LED, then I recommend going to a supermarket and picking up several 100 watt equivalents (they run 15 or so watts each) They are very even lighting with a balanced spectrum, and as much as I hate to say it, far superior to off brand LED panels.
Should you want to continue using LED to grow plants for producing fruit you will need a high powered fixture, that includes all 12 bands of plant spectrum.
As far as nutrients go... Once you change the soil or plant it outside, which it will need soon and given that you are using a soil with good compost, it should not need a feeding. A good soil will feed for a few months.
Here is a comprehensive tomato guide. This will help you to grow tomatoes to their best: https://www.gardeningknowhow.com/edible/vegetables/tomato/growing-tomatoes-guide.htm