Marin Master Gardeners
University of California
Marin Master Gardeners

Marin IJ Articles

Growing shrubs and small trees in containers

February 19, 2011
Julie Monson

THE DIFFERENT HOUSES we've lived in over the years have had either a front porch, entryway, patio or deck, or sometimes all of these, on which I stashed large pots of evergreen shrubs or small trees. More than decorative, they added elegance to something plain, and a welcome to our entry or patio.

In the beginning, I learned that I preferred two or three large containers filled with healthy shrubs to a succession of little pots brimming with blooming annuals. I gave up flowers for a bolder architectural statement made with large containers and handsome evergreen shrubs and small trees. A few bloomed — gardenias in Southern California and Meyer lemons — but the effect was subtle. For flowers, I rely on the rest of the garden.

This kind of gardening can be very satisfying and, once it is in place, easy to care for. One key to success is finding the right containers; the really gorgeous ones tend to be expensive, and the cheaper ones rather clumpy. Over the years I've collected a few and treat them gently. My first choice for up to 21-inch pots is glazed ceramic. We also had two 21-inch wooden boxes made for the Japanese maples on our deck. Large containers need to fit the architecture and style of their setting, so I avoid bright colors or patterns, though these might fit in someone else's house. Be sure each pot has at least one hole drilled in the bottom for drainage.

A large, deciduous mulberry tree grew at the edge of a large patio in the back garden of our Southern California house. It provided copious shade in summer for my collection of container plants (bamboo, gardenias, camellias, Japanese maples); in winter, they received the right amount of weak sun. The lesson is selecting plants that thrive in the mini-climate where you plan to put them.

In West Marin, where we now live, I have one sunny, warm place on our patio for two Meyer lemons that are thriving nicely. Gardenias, to my sorrow, didn't make it. Six pots of bamboo are doing well, as is a large Fatsia japonica, in the same pot it has lived in for at least 18 years.

Planting: A good soil mix is critical and over the years I've developed one that mixes a shovelful of native soil with a good planter mix, sometimes adding peat moss to keep it light. Drainage is key. It's easy for container plants to become compacted. The native soil is for the minerals in the soil (which planter mixes don't always have). Because the soil level will reduce over time, you can fill the container to within about an inch of the top. In a year or two it will have declined considerably. You should mulch with additional compost or an enriched planter mix as needed to maintain
the soil level near the top.

To ensure good drainage, place large pots (more than 15 inches) over two 1-inch boards cut to fit beneath the pots. This allows water to drain easily from the drainage hole. If the pot seems soggy, turn it on its side and slide a pointed tool (like a screw driver) into the drainage hole to make sure it is not clogged.

Maintenance: Have handy a garden hose or watering can — container plants need frequent watering, especially in our dry summers. Mulch is important, especially in warm weather, to keep the roots from drying out, and to provide additional nutrients. One of the best lessons I learned for container plants is to feed them "weakly, weekly." My favorite fertilizer is fish emulsion, mixed in a bucket with a spoonful of iron chelates (Meyer lemons need extra iron). In addition I sprinkle several spoonfuls of a general-purpose granular fertilizer in each pot about twice a year.

Pests: Healthy plants attract few pests. For the occasional infestation, I spray with water once or twice and that works. Slugs and snails I gather by hand.

Pruning: Shaping is best managed by judicious pruning, especially during the growing season, but also throughout the year. Some shrubs, like pittosporum, can be cut back fairly hard to create a rounded shape. They grow back quickly and look scraggly for a short while. Other, more open shrubs, like Meyer lemons, need more gentle clipping of excess interior
branches and growth beyond the general shape of the bush. I prune my potted Japanese maples in February, removing a few main branches and lots of the upper, bushy small twigs, keeping in mind the overall shape, and the space available for the tree to grow into. Maples are the exception to my rule for using only evergreens. A small tree with an interesting branch structure, they don't appear awkwardly bare in winter.

Cleanup: Even container plants require some weeding and I regularly clean out fallen leaves and other debris, often followed by an application of mulch, which is functional and looks nice. Every so often one has to wash off the outsides of the ceramic pots, especially after heavy rains.

Container gardening encourages experimentation with different plants and combinations near your home, on entry or deck.

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