Answer: Since two seem fine but the third is not doing as well, I suspect there may be a problem with that particular plant. It just might not be rooting well underground for some reason, there might be a large rock or something beneath the soil preventing it from rooting, or there might be a difference in the amount of soil moisture it is receiving, for example. Since it is a new plant, I would suggest you consult with the retailer where you purchased it to see if there is a warranty. In the meantime, all you can really do is make sure to water it thoroughly as needed to keep the soil evenly moist yet not sopping wet. Fertilizer would not be helpful to a plant that is already stressed. If it ends up needing to be replaced, it is better to do it now than to wait. The reason here is that earlier in the spring is a better time of year for new plants to become established; by early summer the weather begins to turn hot and that is very stressful on new plants. I hope this helps.
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