If they have been in the pots just a year they will probably be OK. I don't repot every year with new soil, but, if your plants don't perk up when you take them outside in the spring time or they look lethargic, it may be time to repot with new soil. I usually repot about half my plants each year, move them up a size in pot, or root prune and then add new soil.

What kind of plants are they? The soil should be good for up to several years - I don't repot every year either. If you are referring to the fertilizer mixed into the soil, check the bag - I have seen different formulations but generally it's only a 30 to 90 day supply of timed-release fertilizer, so after that you'll need to supplement.

By the way, in the last year or so, MiracleGro seems to have changed their formula for the moisture retentive soil, so that it is now almost TOO moisture retentive for many plants. I switched to ProMix and I like it much better, nice and fluffy.

Most soil mixes contain lots of peat, which after about 2 yrs becomes a hazardous (to plants) muck, so repotting is definitely in order after about 2 growth seasons.

they should be good unless you thing they've over grown the pots and need to be transplated into a bigger one, or if it seems like the soil isnt helping that plants grow well. but other than that you should be good