The lowest winter temperature you can expect in USDA climate zone 9 is 25 degrees F, and it doesn't often drop that low in cities such as Houston, Texas and St. Augustine, Florida. Zone 9 also includes desert regions of the Southwest, including Las Vegas and Phoenix. The hot, dry conditions and porous, sandy soil in zone 9 are conducive to many medicinal herbs, such as lavender, echinacea, vitex, wild yam, saw palmetto and many others. On the other hand, some medicinal herbs require cool winters: you won't have success growing herbs such as ginseng in zone 9.
Prepare a planting area in a sunny spot. Spread a 2-inch layer of organic compost over the area and then turn it under, mixing it with the topsoil to a depth of about 8 inches.
Dig planting holes with your trowel that are slightly larger than the rootball of potted medicinal herb plants. If you are planting seeds, make furrows in your prepared area with a hoe and then sow seeds the correct depth and distance apart, following seed packet instructions.
Water the area well by running a sprinkler for 20 to 30 minutes. If you know that snails or slugs are a problem in your garden, scatter diatomaceous earth or iron phosphate granules over the area after you water.
Fertilize your medicinal herbs about one month after you plant them with a balanced plant food with an N-P-K ratio of 10-10-10. Use compost or worm castings as fertilizer if you want your medicinal herbs to be strictly organic.
Protect any potentially frost-tender medicinal herbs if the forecast for nighttime temperatures is into the 30s. Cover your plants with floating row cover or simply prop a blanket or tarp over them. Remove it in the morning after the temperature rises.