I use the following: https://www.amazon.com/dp/B01LZDOLRI/?coliid=I3OH4MV3I6PEG5&colid=3EQL5K6UCL9FP&psc=1&ref_=l

It's much higher quality than Miracle-Gro you get in the big box stores. As I usually sift out the smaller particles, it ends up costing me about the same. However if your not as particular than it can be pricey (It's like 6x the cost of the above per quart).