Answer: I think you are probably overwatering by quite a lot. Overwatering causes root damage and that then shows as foliage symptoms. Overwatering can cause foliage loss especially from the bottom up, so that might well be the cause.
The soil should be moist like a wrung out sponge, not sopping wet or saturated. To know if you need to water, use your finger to dig into the soil under the mulch and see. If it is still damp, you do not need to water yet.
There is no set schedule for watering. In the spring you may not need to water very often since it is rainy and the ground is naturally wet. In late summer when it is hot and dry you might need to water more often, maybe as often as every four or five days. It is best to avoid daily watering in any case. When you water, water thoroughly and slowly so it can sink in and encourage deep roots. After you water, wait a few hours and then dig down to see how far the water went (or didn't go). This can be surprising.
I hope this helps. If it continues to brown, you might want to check with the store where you purchased it.
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