Asparagus is a perennial and is difficult to grow in northern climates with extended freeze periods. Hard freezes can damage the root system. If you decide to plant in a northern climate, you must insulate the containers with snow and straw mulch over the winter months. In southern climates this is not an issue.
Plant 3 weeks before last frost date for your area. Use a large, deep container. We use a 20 inch round by 17 inch deep container. You can use even larger ones if you wish. You can start from seed but is much easier to buy the roots and plant them. Fill the container with 7 inches of potting soil in the bottom of the container. Make 2 rows and plant 3 to 4 roots in each row. Lay the roots flat in the rows. Cover with 3 inches of soil. Once the shoots pop out of the soil, cover again with 3 inches of soil. Repeat this one more time until you are 1 inch below the rim of the container.
The asparagus will be ready to harvest modestly 2 years after planting and can be fully harvested the third year and many years thereafter. You must wait this long to allow the root system to grow. After that, harvest every year in mid to late spring. Snap the spear at ground level or cut with a sharp knife 1 inch below the surface of the soil. Harvest when spears are about 4 to 6 inches long before the scales at the top begin to open. This will insure the stalk is still tender. Harvest often for about 3 weeks and then allow the plants to grow.
You will see ferns growing in the fall. Do not cut these back until they senesce (die naturally). At that time cut them back to ground level.