Question
We are trying to grow impatiens from seed.
We find instructions such as:

fed from the time when the cotyledons are fully expanded to time of transplant at a rate of 50 to 75ppm nitrogen with a fertilizer such as 15-16-17 or 20-10-20.

I understand fertilizer's N-P-K ratios, but what does 50-75 ppm mean ? If you buy a regular 15-15-15 houseplant fertilizer (in fluid form) how many ppm would be applied and how can you adjust the ppm .. more importantly how can you check/control the ppm ?

Thanks.
Kenneth

Answer
it's parts per million. don't worry about it. on the label it will tell you how many teaspoons, tablespoons, ounces per gallon of water you should mix. most mixes 15-15-15, 20-20-20, etc. will tell you to mix 1/4 teaspoon of fertilizer to 1 gallon of water for indoor plants. don't mix it too strong. that can really hurt the plants. normally you don't have to fertilize annuals from seed until 2-3 weeks after plants emerge. try to keep the fert. off the foliage.