Identifying a good shrub for your containers will depend on your weather conditions and how sheltered your porch is from sun, precipitation and wind. Because your shrubs are in pots rather than in the ground, they will experience greater temperature extremes. To increase the odds of your shrubs doing well during harsh winters, choose a shrub that is two U.S. Department of Agriculture zone hardier than your climate. Hardy evergreen shrubs for a porch container include Mugo pine (Pinus mugo) hardy to zone 3. Shrub dogwoods with colorful twigs (Cornus sericea) are hardy to zone 3 and Weigela florida "Minuet" is a flowering deciduous shrub hardy to zone 4.
Containers left out all year must resist cracking if you live where there is freezing weather; such planters may be costly, so choose slower-growing shrubs to prolong the time they can remain in the same planter without repotting. Some classic slow-growing evergreen choices are boxwoods (Buxus spp.), dwarf conifers (various genera and species) and junipers (Juniperus spp.). Some especially desirable cultivars are "Green Mountain" boxwood and "Blue Star" juniper, notes Muffin Evander writing for "Fine Gardening." Deciduous flowering shrubs that you can grow in containers include dwarf hydrangeas (Hydrangea macrophylla cultivars, such as the Citiline series) and roses.
Shrubs with low water and fertilizer needs are also ideal for porch containers. Water leaking onto the porch is always an issue, no matter how carefully you place your plants. Dishes under the plants may keep the roots too wet or fill up with rainwater during storms, so a shrub that requires minimal watering is ideal. Similarly, container plantings are at the mercy of gardeners to provide necessary nutrients, so less fertilizing means less work. Shrubs that can tolerate dry conditions and poor soils include evergreen yuccas (Yucca spp.) and deciduous dwarf crape myrtles (Laegerstroemia spp.). Note, however, that you must provide a sunny porch location for these containers.
To give hardy shrub plantings added interest, switch out seasonal plants such as spring bulbs, or summer or winter annuals. Carefully chosen perennials can be long-term companions for your porch shrub containers. Consider using your shrubs as a base for porch displays; for example, group pumpkins around an evergreen shrub, or string holiday lights on a deciduous shrub's branches.