Answer: Premixed potting materials vary widely in their ingredients. You might want to use a soilless potting mix developed for container planting (these hold both air and water well without compacting) and also use one of the water holding polymer additives to help make sure the pot does not dry out too fast in mid summer when it is so hot. Even if you use a soil based mix, you will still need to fertilize often to compensate for the leaching that occurs in container planting. You could use a water soluble fertilizer according to the label instructions and/or top dressings of compost no matter which soil you start with.
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