1. Contact your local Master Gardeners or do an online search for a planting calendar specific to your area. Container plantings should be made according to the planting calendar, at the same time that you would plant them in a regular garden. Consult http://cals.arizona.edu/pubs/garden/az1005.pdf for an excellent Arizona veggie calendar.
2. Before filling your pot with soil, ensure that it has enough drainage holes. Add more, if necessary. Cover the holes with permeable screening to deter insects from making a home in your pots, and to prevent soil depletion. Old window screens or coffee filters work well.
3. Fill the container to within 1 inch of the top. If transplanting, make a hole for the plant that is slightly wider and as deep as the root ball (don't plant too deep! Exception: tomatoes.) Do not place fertilizer in the hole.
4. Gently turn the plant upside down and ease the root ball out of the nursery pot, being very careful not to damage the stem. Tease roots apart or "butterfly" any circling roots and place the plant in the hole (see photo.) Make sure that the root ball makes very good contact with the potting soil, leaving no air gaps or pockets.
5. Return displaced dirt to the hole to fill in empty areas. Do not press or force the dirt into the hole.
6. Label with the name of the plant, date of planting, and days to harvest (if applicable.)
7. Gently water, being careful not to displace soil or seeds. The soil may settle, revealing low spots, or the plant may tilt to the side. Add a little bit more soil, as necessary, and water in again. Cover with mulch.
8. Thin seedlings when they have 2 leaves, spacing them according to the seed packet instructions.
9. If cages or other supports are needed, provide them when the plant is small.
Watering: Pots tend to dry out quickly, particularly small pots and clay pots. Water your plants until liquid runs out of the bottom of the pot to prevent salt build-up in your soil. To facilitate draining, place the pot on small legs or in a shallow dish filled with gravel. Allow the soil to dry before watering again (but not so much that the plant can't recover!) Roots need air, so a water-logged plant will die just as quickly as a dehydrated plant. Too much water also encourages the growth of mildews and molds.
In the summer, you will have to water often. In order to help your plants survive the summer, elevate them off of a hot patio and cluster them so that they can shade each other with their foliage. Mulch the top of the soil with wood chips or pebbles to decrease evaporation and keep the soil cooler. Clay pots placed in full sun can get very HOT and bake your plants' roots. Wrap the exterior with burlap, or "double pot" them to create airflow between the two pots.
Fertilizing: Commercial potting soils generally have enough nutrients to last a couple of months. Following this initial period, add water soluble fertilizer according to the package instructions (I prefer to fertilize twice as often at half the recommended strength.) Do not over fertilize as plants can be "burned" by too much nitrogen. For optimum performance, refresh your pots annually with fresh compost or other organic material. Note that fertilizers list the big three nutrients (nitrogen, phosphorous and potassium) in the order N-P-K on their packaging (such as 15-11-8.) Flowering plants need phosphorous to bloom, so choose a fertilizer with a high 2nd number. Use a balanced blend for green plants and shrubs , such as 20-20-20. Acid loving plants will appreciate the addition of soil sulphur (coffee grounds are acidic, too.) Cactus and succulents only need to be fertilized once or twice each year, while they are growing.
Light: Choose the right plant for the amount of sunlight that your pot will receive. Some plants grow well in shady areas. Others, such as vegetables, require 6-8 hours daily of direct sunlight. Plants that require full sunlight in temperate areas may appreciate some afternoon shade in the summer. If your plant is too shaded, it may yellow or become "leggy" as it stretches to reach the sun. Sunburned plants turn yellow or brown. Move them, as necessary.
Salt damage: Phoenix water is high in salts, and container plants are particularly vulnerable to salt damage. Water deeply to prevent salt build-up in your pots. If you notice leaves with brown edges or tips, this is a sign of salt damage. Flush the pot well to wash salts away from the roots and out of the pot.
Care: Keep an eye out for insects, particularly on vegetables. Remove them manually or chemically, if necessary. A solution of 3 tsp of Ivory dish soap to 1 gallon of water will deter many pests. Trim off dead or diseased plant material. "Dead head" flowers to encourage more blooms. Prune growing plants or move them to a bigger pot, if necessary. Refresh your pots annually with new soil and mulch, washing them with a 5% bleach solution between plantings.
Container gardens can dry out very quickly, especially in the intense heat of the Phoenix summers. An automatic watering system will allow you to leave your plants for a vacation and prevent an "oops" if you are unable (or forget) to water. Consider automatic watering as a life-support system for your plants that will require some monitoring to ensure that it is working properly and watering at the correct rate. Occasional, deep hand watering may still be necessary for optimal plant health.
It is easy to add a drip system on a timer to your patio faucet. Kits are available at garden centers and big box stores, as well as irrigation stores. Some even provide clear plastic tubing that "fades" into the background. When you install your system, add an inexpensive timer that will turn the system on automatically at intervals that you set and are able to change as the seasons demand
Just about any container that can hold soil and water can become a flower pot, from buckets and boots to bags and wine barrels. If it is impossible to add drainage holes to your container, place a slightly small pot inside the container, propped up on bricks for pebbles to allow for drainage.
Note that metal containers are not recommended for plants that will be outside in the sun in Arizona. They tend to get too hot for tender container plants
For further information on container gardening or gardening in arid, desert climates, I recommend reading the following resources. If I were to chose ONE book as a reference, I would choose "Desert Gardening for Beginners," which was required reading when I was studying for my Master Gardener certification. I regularly buy this book to give as gifts to my gardener friends.