Answer: If you have been growing a geranium indoors you could replant it in the garden, yes. You could also take tip cuttings and root those for planting in the garden while saving your houseplant geranium indoors.
Allow the plant to become conditioned or acclimated to outdoor conditions before you plant it, the process takes a week or ten days. Do this by setting it in a sheltered and shady location outdoors for a day or two, then expose it to a bit of early morning sun. Increase the amount of sun each day until you have it in direct sun all morning. Then you can plant it. Be sure all danger of frost is over with before you set it outside.
The little gnats are probably fungus gnats. These breed in damp soil such as houseplants have. To stop them, use a soil drench such as Gnatrol (read and follow the label directions) or cover the soil surface with a layer of sand or gravel. The fungus gnats breed in damp soil, but the sand or gravel dries out very quickly and prevents them access to the damp soil beneath. This stops their breeding cycle. It takes a week or so for the adults to die off. Also be sure you are not overwatering your house plants.
I hope this helps.
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