Tips and Tricks for Container Gardening With Conifers
Container gardening is perfect for anyone confined to a balcony or deck and is also a wonderful way to add color, dimension, and versatility to any landscape, large or small. We all know that a well-planted, well-placed container can make an outstanding garden accent or dress up patios, decks, entryways, and windowsills to perfection. There’s an art to container gardening—techniques and tricks to ensure that your container-grown plants thrive. Temporarily, you can make almost any plant work in almost any container, but for long-term success it’s important to combine the right plant with the right pot, to work with your chosen plants’ growth habit, and to abide by each plant’s exposure, soil, and watering preferences. Container gardening with conifers is no exception.
Knowing what your tree needs and being determined to provide it, you can plant any conifer in a container, but growing a full-size specimen presents a number of challenges. To begin with, you’ll need to repot it every two years into an even larger container, or you’ll have to learn how to root-prune or even bonsai it to curtail its growth. Most conifer lovers tend to give up when faced with the stress of keeping a vigorous, full-size tree happy in a pot, almost invariably planting it out in the landscape within two or three years. But there is a better way!
Opt for dwarf specimens over full-size varieties
Offering the same color, texture, sculptural form, and evergreen beauty as their full-size counterparts, slow-growing miniature and dwarf conifers allow for a more stress-free way to garden in containers. They also require a lower-maintenance approach and ensure success both for the conifer itself and for the gardener. Most dwarf conifers grow so slowly that they can thrive for many years before outgrowing their original containers. There’s currently a dazzling selection of dwarf conifers available in an array of gorgeous hues and in forms ranging from soft, rounded globes to narrow, sturdy, upright spires. I’ve narrowed the field to my top five picks below. Combine any one of them with your own favorite container, follow these simple growing tips, and you too can look forward to many years of evergreen enjoyment.
‘Golden Mop’ threadleaf cypress
‘Golden Mop’ threadleaf cypress (Chamaecyparis pisifera ‘Golden Mop’, Zones 5–7) has threadlike golden foliage that radiates outward from the center. This well-behaved, compact, low, mounding shrub is fabulous in the landscape or a large container; it adds vibrant color and soft, touchable texture anywhere it’s grown. Sited in sun to partial shade (it maintains its color better in full sun), this beauty will reach 6 to 8 feet tall and wide at maturity.
‘Cole’s Prostrate’ Canadian hemlock
‘Cole’s Prostrate’ Canadian hemlock (Tsuga canadensis ‘Cole’s Prostrate’, Zones 3–7) drapes itself over the edges of the perfect pot. A tough, slow-growing conifer with a cascading habit, it ultimately reaches 6 inches tall and 3 to 4 feet wide. Best to grow it in afternoon shade in NorCal.
Blue prostrate noble fir
Blue prostrate noble fir (Abies procera ‘Glauca Prostrata’, Zones 5–7) is slow to reach its ultimate size of 3 feet tall and 6 feet wide. With its steely, blue-green foliage carried on semi-spreading, semi-upright, extremely sturdy branches, it is a beauty. Make statement in full sun (with diligent watering), or for a more stress-free experience, grow it in afternoon shade.
‘Picola’ Japanese umbrella pine
‘Picola’ Japanese umbrella pine (Sciadopitys verticillata ‘Picola’, Zones 4–9) is stunning, with a dense, upright, conical growth habit and short branches that carry attractive whorls of long, shiny, dark green needles. Slow-growing, measuring just 4 feet tall and 3 feet wide at maturity, it can tolerate sun but does better in afternoon shade in warmer regions.
‘Jean’s Dilly’ dwarf Alberta spruce
Create a miniature forest of ‘Jean’s Dilly’ dwarf Alberta spruce (Picea glauca ‘Jean’s Dilly’, Zones 3–6) by planting multiples in one huge container. This is a lovely upright, conical conifer with impenetrably dense, fine-textured, green foliage. With such a slow growth rate (at maturity, it reaches just 3 feet tall), it may never need repotting. It does best when shaded from the hottest summer sun but looks fabulous in any exposure when dressing up winter holiday porches or entryways.
Pick the right container
When choosing a pot for your tree, consider the mature size of your conifer and both the current and future size of its root system. Pick a container proportional to the tree’s current size (twice as wide and 50% deeper is a good rule of thumb), but with adequate root space for at least three years of growth. Too large a pot ends up causing almost as much trouble as one too small. In warmer regions of Northern California, the container’s color is also important, with a lighter-colored container preferred because of its heat-reflection qualities. This helps maintain the cooler soil (and thus root) temperatures favored by dwarf conifers. Good drainage is vital, so ensure that the container has ample drainage holes.
Not just any soil will do
The soil should be loamy, humus-rich, and slightly acidic (a bark-based potting soil is ideal). It should hold adequate moisture yet drain well. I make my own potting mix for container-grown conifers and have achieved consistent success using 5 parts high-quality organic potting soil mixed well with 1 part fine fir bark. Mulching is always a good idea and will help keep the tree cooler and weed free. It will also aid in moisture retention.
Keep the water and the fertilizer light
When grown in pots, conifers (like all container-grown plants) need a regular watering schedule throughout the year, with extra diligence during the growing season, heat waves, and dry periods. During the growing season, apply a weak (quarter-strength) solution of well-balanced, water-soluble fertilizer to the soil surrounding your dwarf conifer every four to six weeks. Alternatively, a yearly application of a 2- to 3-inch layer of organic compost in spring will help keep your tree happy.
A little bit of shade will be most appreciated
Though most conifers are said to prefer full sun, I’ve found that in the warmer regions of Northern California, a container-grown conifer is less stressed if it is shaded from summer’s hottest afternoon sun. A container also offers you the option of moving it into a shadier location for the summer months. In cooler and coastal parts of NorCal, a full-sun location is fine.
For more on growing conifers in containers, go here.
—Fionuala Campion is the owner and manager of Cottage Gardens of Petaluma in Petaluma, California.