Wednesday, October 31, 2007

Alternative to Dwarf Alberta Spruce in Containers

I recently ran into a friend who had a good question about evergreen plants for containers. Outside of where she works in Brooklyn, a small retail shop, they have two large pots that are about 16" or 18" inches in diameter. She described the small trees planted in them at present and I was able to assess that they were dwarf Alberta spruce, Picea glauca 'Conica'. Dwarf Alberta spruce are slow-growing, short-needles evergreens that grow in a very conical habit and are quite popular for use in containers. If you see one in passing you might say it looks like a perfectly miniature Christmas tree. Liz was concerned because they were developing many brown patches and beginning to look pretty rough. She was wondering how she might fix the situation and if the trees will bounce back. I asked about sunlight to the area where the pots are situated and Liz said that there is partial sun and definitely some shade. Spruces of different shapes and sizes are attractive evergreens because of their sturdy needles, dense growth habit, and slow rate of growth. The photo below is a small containerized spruce (not a dwarf Alberta) that I saw in the Flower District on 28th Street.
The catch with spruce is that they need to be grown in a full sun application to do best. By this I mean they need at least 4-6 hours, if not more, of direct sun daily. If they are in too much shade, they begin to thin themselves out from the bottom up so that they can have the most efficient amount of needles working for the relative sunlight they receive. Unfortunately most coniferous trees, such as spruce, do not rejuvenate and put out new growth from their lower branches like herbaceous or broadleaf evergreens might. Therefore I recommended to Liz that the trees be pulled out of the containers and planted somewhere where they will get more direct sunlight. She had an idea as to where they could go and said she would move them. I recommended that she prune out the dead branches, that they would most likely not produce needles again, and hope that over time as the remaining branches grow and spread that they might fill in the holes that are presently there. However, Liz then had one last question. What can I plant in the containers that will do better?

A reliable option, and a selection of plants typically easy to find in the city, various hollies (Ilex) are excellent plants to use in containers with part shade. This is a containerized Japanese holly (Ilex crenata) I found while down on 28th Street that I think might be a good option.

It will grow a few inches a year and will keep that overall shape that is rather conical. Eventually it will want to be replanted to a garden, but for a few years it would hold up in an adequate sized pot with ample drainage. If you wanted an even slower grower, you might also consider boxwood (Buxus sp.).
Boxwood and Japanese holly may look alike, but there is one way of telling the two apart. Take a close look at the small rounded leaves produced by each broadleaf evergreen shrub. If you touch the margin, or edge, of the Japanese holly leaf you will feel a very slight serration, while the margin of the boxwood leaf is always completely smooth. Boxwood are slower growers compared to most hollies but it will do just as well in a container in part sun or shade. In either case you could plant these shrubs in the pots out front of your work for some instant structure and then plant annuals or vines around the edge for an extra added shot of color.

There are other options as well and we can discuss those further. There are larger leafed hollies that hold up well in containers in the city, but eventually they will get large and need to be planted in the ground.
Variegated plants, with two-tone leaves, are attractive because they provide different color and texture within one plant, but it is helpful to know that variegated plants often require more sun. If you think about it, the white, or light parts of the leaves do not have as much chlorophyll in them as an all-green leaf might, so they often need more sun to efficiently photosynthesize and grow. Grasses can be great too, especially for their potential fall color, and again, I am more than happy to discuss some of those options as well. Best of Luck.

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