Hi, Emma. I too live in the deep south, NE Mississippi. I am also a Certified Mississippi Master Gardener, so let's see if anything I tell you is helpful. Iris's are not something I grow a lot of, but have some in my landscape. My expertise, if I have any at all
is with tropical plants, particularly orchids, plumeria, staghorn and elkhorn ferns, and fiddleleaf ficus.
Iris's need a good, organic foundation to grow and bloom well. I pretty much make my own "soils" and potting mixtures for my various plants, and for iris's I would make a mix of 1/2 garden soil (top soil will be fine), 1/4 milled sphagnum moss (peat moss will do), and 1/4 compost. If you don't have a supply of compost, use something like 'Black Kow'. You can find it at the big-box stores, such as Lowe's. That formula is not complicated and all ingredients are easy to find.
Iris's like moisture, lot's of moisture, so you want your soil to drain well but at the same time hold moisture. During the summer's heat (you have the same problem - hot) I try to water my plants every single day to keep them hydrated. Water in the early morning if possible, since the ground will not be so hot and the water will not evaporate so quickly.
In late winter, before the iris's begin to sprout, I apply a blooming fertilizer. When they sprout, I again apply this fertilizer. I don't fertilize again until they have quit blooming and then switch to a general purpose fertilizer, such as 20-20-20. I will apply that at recommended strength (generally 1 tsp/gal). I use this every-other-week for perhaps 6-8 wks. I also like Osmacote, 3 month slow release fertilizer, since I only have to apply that once. The blooming fertilizer helps with blooms and the general purpose fertilizer helps strengthen the bulb and maintain it during the fall and winter.
Some iris's will bloom just fine in part shade but some want full sun, 6-8 hrs. minimum to bloom well. It just depends on the hybrid(s) you have.
I hope this will be of some help. Ken
