Answer: Browning can be a sign of over or under watering. It can be a sign of transplant stress, or planting too deeply, or poor rooting. It can also be a sign of pest or disease, or even accidental herbicide or chemical exposure; it can be a sign of overfertilizing having "burned" the roots. (Fertilizing generally will not help an ailing plant, it stresses it further.) I would suggest you begin by checking the soil moisture. Dig into the soil with your finger, checking both the potting soil and the surrounding soil. It should be evenly moist or damp like a wrung out sponge. It should not be saturated or sopping wet.
Junipers and pines both need a well drained soil, meaning one that holds both air and water so it is not sopping wet or saturated. New plants however root best into soil that is evenly moist. So you need to water carefully in that you do not want to over water. You would not want to plant them in heavy clay or in a low spot for the same reason. While adding sand can improve the drainage to some extent, it will not work in the long run when the roots extend out beyond the planting hole. And, in clay soil, you can end up with a sump collecting water at the bottom of the drainage hole.
Check the soil with your finger. If it is still damp, don't water. Your goal in watering is to supplement rain, if needed. When you water, apply it slowly at the root area so it soaks down deep to encourage deep rooting. After you water, wait a few hours and then dig down to see how far your water went; sometimes this is surprising. It is better to water deeply less often than to sprinkle lightly every day.
You should also be using an organic mulch in a flat layer over the root area, it should be several inches thick and should not touch the trunk or stems. This will help keep the soil evenly moist, hold down weeds and also feed the soil as it breaks down slowly over time.
Since these are new plants, I would also suggest you consult with your retailer as to why they are browning. Good luck with your plants!
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