Arborvitae and Geraniums

Chinese arborvitae (Platycladus orientalis)

Chinese arborvitae (Platycladus orientalis)

Geranium maderense (photos by Virginia Snow)

Geranium maderense (photos by Virginia Snow)

Two weeks ago, I purchased several 3-foot tall arborvitae. I want to transplant them into 24-inch square containers. Is this a good time to do so? What soil mix and fertilizer should I use? I also have a lot of geraniums that are growing well. Is this the proper time to cut them back?
>Melanie Grey, Camarillo
Oriental arborvitae (Thuja or Platycladus orientalis), a shrubby conifer, is easily recognizable for its pyramidal shape and scaly, yellow-green foliage. Depending on the cultivar, oriental arborvitae grows 4 to 8 feet tall. It does best in half-day sun and should receive average water.
You can transplant almost any species from one container to another this time of year, just before plants begin to grow in earnest. In the manner of conifers in general, arborvitae requires excellent soil drainage.
I would make a mix consisting of one part plain washed sand, available by the bag at any builders’ supply center, and three parts potting soil. In place of sand, you could also use topsoil, available by the bag at nurseries and home centers. You can also purchase a 50/50 mix (half topsoil, half compost) by the cubic yard at Valley Sod in North Hills. This mix would also be suitable for growing most plants in containers.
The only problem with topsoil is that the water that drains through it stains the surface underneath. If you are placing your pots on a concrete, wood or tile deck, avoid using topsoil in the mix. You could use large catch basins or dishes underneath your containers to hold the water that runs through, but it is healthier for container plants to grow without dishes. Standing water in a dish underneath the pot can lead to fungus problems and encourage insect pests.
Be aware that the volume of potting soil in a container shrinks with the passage of time, especially if you have a dark, highly composted mix. Over time, organic matter breaks down and volatilizes into the air. There is also considerable settling and compacting that takes place with rich and fluffy soil mixes.
As for fertilizers, any formulation that contains 20 percent nitrogen or less is acceptable. The nitrogen percentage is the first of the three numbers, separated by dashes, on the fertilizer bag, the next two being phosphorus and potassium. More than 20 percent nitrogen is suitable as a lawn fertilizer but leads to rank growth, an invitation to insect pests, when applied to ornamental plants and vegetables.
The geraniums to which you refer actually are pelargoniums, native to South Africa and members of the geranium family, of which there are several types.
Zonal or fish geraniums (Pelargonium hortorum), with strong flower colors, an upright growth habit and softly lobed leaves, are the most commonly seen. In our area, they bloom most heavily in the cooler months, but may be seen flowering on and off throughout the year.
Martha Washington geraniums (Pelargonium domesticum) have crisply cut leaves, glowing flowers, and bloom exclusively in late winter and early spring. Scented geraniums — of which there are many species and fragrances including mint, lemon, apple and nutmeg — are grown as aromatic filler plants with variously shaped leaves whose flowers, incidentally, are usually nondescript.
Lastly, ivy geraniums (Pelargonium peltatum) are best suited for balcony planters and, secondarily, as long-blooming ground covers.
Geraniums/pelargoniums may be cut back any time of the year, but it is wisest to do so in the spring.
All pelargoniums propagate easily from stem and shoot tip cuttings.
Tip of the week
Although they do not make the loud splash of pelargoniums, true geraniums are especially savored, for foliage and flowers, by plant connoisseurs.
Chief among these is Geranium `Johnson’s Blue,’ a mounding hybrid that spreads delightfully and surreptitiously by means of rhizomes. Its flowers are 2 inches across and violet-blue, accompanied by snowflake foliage.
Geranium incanum is a ground cover with delicately cut foliage and rose-violet flowers. It is a low-growing, billowy ground cover that moves softly through the garden, self-sowing where the soil is well-drained.
Geranium maderense is the most dramatic member of this family, with deeply cut leaves growing to 8 inches. The plant may reach several feet in height, topped off by a rich bouquet of pink flowers which are its swan song, since it dies as soon as flowers fade. It, too, self-sows in the garden.

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