In my experience, a spray bottle isn't a good watering device. When you water, you want to pour enough water to at least cover the surface of the soil in the pot by about (hmm -- eyeballing it here -- 1/2 inch for a small pot to 1 inch for a large pot). Ideally, keep a saucer under the pot and pour water in, wait and see if water comes out of the bottom, allow to sit for a couple of hours to see if the water is absorbed back by the soil, then empty the saucer. Catnip DOES like it on the dry side, as you seem to know.
I usually check if a pot needs to be watered by the "lifting" method -- heft the pot -- water if light, water a lot if too light, don't water if heavy. You'll get the "feel" for it after a while.
You see how, using a spray bottle, you'll be spraying that plant for a long time to achieve the amount needed. Spray bottle is good for raising humidity around humidity-loving plants. In fact, most hairy/fuzzy plants (like catnip) don't like getting their foliage wet very often. It's also good for soapy mixture (use liquid soap, NOT detergent) to spray insect pests like aphids, white flies, scales, fungus gnats, etc. (You'll want to rinse with plain water afterward so your kitty doesn't get soapy catnip!)
Now, when you say you used garden soil -- what kind of soil was it? Most of the time, unless you have a relatively sandy soil, garden soil is too dense/heavy for container plants. If you pour your water in the pot and the water just sits there on the top and doesn't soak in in the next couple of minutes, this soil is way too heavy for catnip (or any container plant for that matter unless it's a REALLY moisture loving plant). When your plant is NOT wilted, slip the soil ball out of the pot, gently pull the soil away from the roots, then mix the soil with about same amount of sand (or perlite or vermiculite). Mixing coffee grounds is fine -- probably not much more than 2 tablespoons per cup of total soil volume, or just spread a layer on the surface and gently scratch in with a fork. Catnip doesn't need nutrient-rich soil though, and I tend to think catnip would prefer soil that is
not lower pH. (For flowering plants that like acid soil or tropicals, I might add more -- as much as maybe 1/4 of soil volume) Re-pot your plant, being careful to put enough soil in the bottom and gently spreding out the roots so that the plant is at the same depth of soil as before (or a little deeper is OK - catnip will form more roots from the stem). Make sure to leave about 1 inch between top of soil to the top of the pot for watering.
Catnip likes a LOT of sun. So keep your plant in the sunniest window sill you have with no window coverings. If you don't have a sunny window, you may need to supplement with artificial light. OH! I just noticed you're from Philippines! OK maybe it doesn't need THAT much sun there, so ignore the "no window coverings" advice. You may do better with somewhat filtered light. Best way to judge -- if if the plant is stretching out for light and the stems are skinny and weak-looking, and there are long stems between leaves, it needs more light. Work on your watering first and see if that corrects the wilting problem.
Hmm. Maybe I should add that sand should be rinsed well with plain water first so it doesn't contain too much salt.
Hope that helps!
