Year-Round Container Gardening: Part One

By Aylce Goldman and Cathrine St.Clair

In this series of articles, we plan to discuss various aspects of container gardening – with an emphasis on using your containers for year-round interest. Part one covers the benefits of year-round container planting, what to consider when selecting a container type, year-round container soils, and some general planting maintenance and design considerations. Future articles will address more specific planting suggestions.

Growing plants in containers can increase your growing space, increase the range of plants you can grow or make veggies and herbs more accessible.  Keeping plants above ground level may make it harder for deer, rabbits, and squirrels to chow down on them.  Year-round plantings in durable containers also provide added interest throughout the long winter season. Containers can also offer a protected spot for smaller plants, trees, and bushes to mature until they are ready to be planted out in the landscape.  Containers can address challenges such as dry shade, poor soils, too much pavement, difficult areas to plant in, or just the need to add more interest to your landscape. 

Container selection

Containers can be made from many materials and some are more suitable for year-round exposure than others. Many types of ceramic (including terracotta) are often damaged by freeze thaw cycles and many plastics become brittle with sun and weather exposure. For year round durability, consider double-walled plastic or heavy glazed planters (Vietnamese glazed pottery ones are especially durable). These are often marked as frost tolerant or resistant. Wood and metal can also be used, although metal containers are less insulating – transferring more heat in summer and more cold in winter.

With containers, larger is usually better. A larger, taller container can accommodate a small tree or shrub with the addition of perennials and annuals – providing multi-season interest.  A larger diameter will help keep moisture and temperature more even during the growing season, insulate the roots of any perennials, trees or shrubs better during the freeze- thaw of winter months, and add stability for wind.  Grouping several larger containers together creates a statement and is much less maintenance than many small containers.

Spring is the best time to look for planters to add to your landscape.  When shopping keep in mind the future location, quantity you would like, and color as well as size.  Most often a grouping of planters in graduated sizes looks best and therefore you may want to buy multiples of a certain color in various sizes.  It is best to buy when you see them so there will be no disappointment if you decide to add more.  Plastic planter colors can be changed with plastic spray paint so if you find the right shape and size, you can alter color to match your collection.

Consider elevating your planters if they are on hot pavement or in an area that has bad drainage or where water can freeze around the base. Pots containing plants that require extremely good drainage are often best elevated. Elevating pots can also protect decking from water damage. There are pot feet commercially available but bricks, stones, slate or even wood can be used. Just be sure not to block pot drainage holes.

Container soil

Purchasing large, durable, all-season containers means that you will probably not move or empty them regularly.  Since the plants will be growing year round in this planter, you want the soil to retain water and feed your plants, yet still drain well to prevent root rot. 

Garden soil will not have enough drainage and aeration in a pot. You will need to use a specific potting soil. Straight standard potting soil is often too sterile for good year-round plant survival and too light-weight for good root anchoring of woody plants. Consider adding some natural materials such as compost, partially broken down leaves, re-hydrated coir, composted bark, or bagged mushroom compost to give the soil a bit more bulk. You may also want to add some sharp sand or chicken grit to improve drainage.

Be mindful of any special needs of the plants you choose. Some may require more drainage than others and some might be sensitive to soil pH. You may need to alter your soil mix or purchase a special soil mix to accommodate them.

Container Maintenance

Once your planters are completely planted, plan to water well, and apply a slow-release fertilizer. Mulching the top of the soil will help retain moisture and prevent weeds.  When planting, leave about an inch between the top of the mulch (or soil if mulch is not used) and rim of the pot. This provides room to water the pot so water soaks in and does not run over the side.

Containers will need more frequent watering than plants in the ground so position containers where they can be checked and watered easily. Even a large container may need daily watering if it is in a hot, sunny spot. It is better to water deeply to encourage roots to spread out in the pot and prevent the build-up of salts in the soil. Water until you see water running out of the base of the pot. If pots dry out completely, the soil can shrink and pull away from the sides of the pot. Then when you water, the water runs down the sides instead of sinking into the soil. You can fix this by placing the pot in a pan of water until the soil is saturated or by adding smaller amounts of water over a couple hours until the soil re-hydrates.

If a container is positioned near a wall or under eaves, it may not get adequate water from rain and will need more manual watering. This is often the case with window boxes.

In a large enough pot and with proper care – trees, shrubs and perennials can happily live for years in a container. Plan to refresh any mulch and slow release fertilizer each spring. And check to make sure the pot is draining properly.

However, you may decide to replace or change plants as the season progresses; swapping out plants that are under performing or ones that are overtaking their neighbors.  If you remove perennials from a pot planting they can be added to your landscape.  Once fall comes around, clearance sales may provide some plants with winter interest to take you through to next season. You can also add spring bulbs to your pots.

General Container Design

When planning your container plantings, consider the containers as part of the overall design.  Look at the shapes, height, and colors of the containers you have chosen.  Keeping things in scale will make your plants look connected to the planter.  Combining a small shrub and a few small annuals will look out of proportion in a larger planter. Using the pattern of high, medium, and low will create an interesting well-balanced look. The lower plants can include both a low annual and a low trailing vine to spill over the side.  Variation of leaf textures, mixes of complimentary colors and plant care requirements should be considered as well. 

Planters are a fun way to try out various plants in a more controlled environment combined with the ability to appreciate them closer at hand.  They are a good way to mix ornamentals with herbs, vegetables or bulbs. House plants can also summer outside tucked among annuals and perennials. If their pots are small, you can nudge them in pot and all.    The possibilities are vast when working with larger, year-round planters to give your garden extra growing space and interest.

We’ll have some more specific planting suggestions in future articles.