Drainage: One of the most important things is to make sure water can drain freely out the bottom of the pot. Containers generally come with a drainage hole but if you are using a unique garden planter such as galvanized metal buckets, teapots, or watering cans you can drill a hole yourself with a masonry, glass or tile bit. To reduce the amount of potting soil that may drain out of the drainage hole, line the bottom of the container with broken bits of terra cotta pots, coffee filters, or permeable landscape cloth.

Size: Small pots will dry out faster than larger pots that hold more soil. This is especially true for hanging baskets. It’s ideal to use at least 12” planters and 14-16” hanging baskets.
Type: Unglazed pots will dry out more quickly than glazed pots. Terracotta pots aren’t frostproof and may crack in freezing temperatures. Plastic pots are lighter weight and easier to move. Plastic pots retain water more effectively than a ceramic pot.

Good quality potting soil is lightweight and drains freely, which is exactly what your plants need to thrive in container gardens.
Use bagged soil or a soilless media designed especially for containers. Leave about two inches of room at the top of the pot when planting so that when you water your planter the water will not run off before penetrating the plant’s roots. High quality potting soil doesn’t actually contain “soil” at all. Instead, it is a mix of things like peat moss, perlite and bark which provide nutrients, good airflow and drainage for your containerized plants.
Container mixes can decompose overtime and become anaerobic so replacing the container mix every 2-3 years is recommended.

Light: Plants in full sun will dry out quicker than plants in shade and will require more frequent watering.
Watering: Watering should be checked daily during warm or windy weather. Plants can dry out a little between waterings, as they will adapt to needing less water as less water is available to them. Plants should be watered prior to reaching the wilting stage. When the first 2-3 inches of soil in planters is dry this is a good indication that your plant needs watering.
Fertilizer: Fast-growing annuals, edibles or heavy feeders benefit from a water-soluble feed during the growing season. Perennials, shrubs and trees benefit from a slow-release fertilizer being applied in the spring.
Wind: In windy sites plastic containers, narrow upright containers, or light weight containers may blow over so ensure you choose a container that is appropriate for your site.

Temperature: Plants in containers do not have the moderating effects of the ground so they experience more extreme temperatures in both the summer and winter. A general rule of thumb is that plants in containers lose 10 degrees Celsius of hardiness so if a plant is hardy to -10 degrees Celsius it will need protection when temperatures reach freezing.
During extremely wet periods it is advisable to move plants under cover to prevent the potting media from becoming soaked.

If water is not draining out freely from your container, check the drainage holes for a blockage and assess compost structure. Container media can decompose overtime and as the organic components decay, compost can become soggy, dense and lacking in air spaces.
Root pruning: For shrubs, trees and perennials that remain in containers for long periods of time root pruning is recommended. This involves removing the plant from the container, loosening and trimming the rootball and then repotting the plant with fresh potting soil
Overwatering is the most common cause of loss of container plants; watering should aim to keep the compost moist, never soggy and avoid alternating dryness and saturation.

Proper Care: How to Care for Your Container Garden

The Best Plants for Container Gardens