I have miracle grow gardening soil as well as Hoffman and Espoma cactus mixes. Can I mix these two (part cactus mix part gardening mix) together for potting geraniums and lobelia? I'm out of general potting mix and am curious if mixing the two together would be an OK alternative? If not, what is the harm or reasons not to?
A few questions to consider; is that soil old, been around awhile in opened bags? Miracle grow potting soil already has fertilizer added. Need to know if any fertilizers have been added any of these soils. Too much fertilizer and too little fertilizer will kill a plant.
Old soil will probably have pathogens or insects in it now. That is a risk. Will this pot be out of doors?
Myself? I would take the risk and use those soils mixed for the potting soil. Do not use any rock or gravel at the bottom of the pot below the soil and above the drainage hole. Just add your mixed potting soils, plant plants, water the soil as you go to moisten all of the soil, not saturate. Do not water again until that soil is dryer and the pot feels lighter. Lobelia loves shade...partial shade. Geraniums love sun. Something to keep in mind. You'll have to put the pot in sun with a little partial shade late afternoon. Cut the flowers off way before the blooms get old. To keep Geraniums blooming you really have to be brutal cutting the flowers off especially at the beginning. Try the lobelia but a better filler would be Ipomea Lime Green. Potato Vine in chartreuse green that would do well with your geranium for sun and water. The Ipomea that is dark eggplant color is also good to combine with the Geranium (red?) and Lime Green Ipomea. An orange sedge or two would pull those plants together well. How big is your pot?