I don't do the Mel's mix but from what I understand you may be defeating the intent of the mix by using the Miracle Grow Soil. It is supposed to be a soilless mix. Substituting two more types of compost for the soil mix would be appropriate to call it Mel's mix. It may do just fine but it isn't Mel's mix.

yeah, not technically Mel's Mix I guess. I just hadn't been able to find other compost varieties. Hopefully it'll still produce some good veggies.

volguy, I bet it will be just fine.

dirtguy, thanks. I'm sure it will do ok at least. Just wanted to make sure I have enough variety of nutrients.

This is my first year with an SFG also. I have 4 boxes, 3 with the 5 compost mix and one with a 2 compost mix. I'm thinking that the plants will decide. Most grow pretty well in plain old dirt, so anything better than that is an improvement. I have strawberries in the 2 compost mix box, and while it is early they are doing just fine. I plan on adding corn in that box as soon as it is warm enough (western Colorado). I'm interested to see if there is a difference in how my plants grow in the boxes and compare how the compost mixes do. I don't think you have to worry. Sunshine and water are just as important as the soil mix.