CONTAINER CULTURE
A guide to growing potted masterpieces to last throughout the season
Now is the time to assemble pots and containers for the rest of the growing season. They’re not just for summer; spared an early frost, tender container plants can still look great at the end of October, so it pays to devote some time and resources to getting them right.
Lushly-planted containers bring the joy of gardening to the smallest of urban spaces. In larger landscapes, they help carry the garden through high summer, when the general show is dulled by the heat. They also have an important design role in announcing an entrance, softening corners and even screening unwanted views.
The popular formula for composing a garden in a pot is to observe the mantra of “thriller, filler, spiller.” The reference is to a single upright specimen (thriller), annuals that trail over the lip (spiller) and others that fill the remaining gaps (filler). Some of my horticultural friends have grown weary of this principle. I think any clear concepts that help people compose with plantings are useful, so I’m not quite as dismissive of the prescription.
Bear in mind, though, that plantings that prioritize leaf ornament and texture above flower show offer stronger designs while being easier to maintain. In shade gardens, this is the only way to go. Leafy tropicals and other foliage plants, including begonias, caladiums, coleus, cannas, ferns, dracaenas and philodendrons, can be used for dramatic effect in the shade container.
Whatever compositional approach you favour, there are general techniques for success.
CHOOSING PLANTS
First, look for annuals that have been branded as superior performers, especially among petunias, calibrachoas and verbenas. They are sold as trademarked series. They tend to flower more and longer and shrug off the stresses of heat.
But even these share the container plant’s overriding need for regular watering, especially when in full sun. That may mean every day in 30 C-plus weather.
If you want to move away from the thriller-filler-spiller doctrine, consider these approaches:
Blending: Ditch the thriller and the spiller, and focus on the fillers so you can create an integrated tapestry with two or three varieties to great effect. You need annuals that are compact, compatible in their growth habit and similar in texture. The Proven Winners brand demonstrates this in one such recipe, with two plants of a yellow bidens, two plants of a rose-pink calibrachoa and one deep-purple petunia planted in a 16-inch (40-centimetre) pot.
Stand-alones: Sometimes all you need is one starring plant in a pot. It should be dramatic in its growth habit, upright, and sculptural or cascading, for example. Discover its end-of-season size before picking its pot — plant and container should be similarly scaled.
There are plenty of choices for stand-alones in either sun or partial shade, including palms, papyrus, elephant ears (alocasias and colocasias), banana “trees,” angel’s trumpet, cordylines and bromeliads.
If the plant is somewhat bare at its base, it may look better with a planting around the edge of the pot, but this choice should be of a single and low-key variety that won’t compete with the main plant. Lysimachias, trailing smallleafed tradescantias, dichondra and sweet potato vines are some choices.
I asked Brian Sullivan, vicepresident for landscape and glasshouses at the New York Botanical Garden, for some of his favourites. One simple but effective example is a scented geranium in a pot edged with a beautiful but underused oregano named Kent Beauty, which has trailing bracts resembling hops. As a sculptural stand-alone, he also likes the foxtail agave (Agave attenuata), cupheas and sticks-on-fire (Euphorbia tirucalli).
Nesting: Another approach is to assemble plant combinations — but in separate pots. That is, have a cluster of containers with each holding its own plant. For best effect, limit the number of containers to three or five, mix up the sizes, and have a clear starring pot. Avoid a gaggle of small, samesize pots, which will look busy and unplanned. Pot groupings are particularly useful in hard-edged corners, at changes of elevation or at important portals in the garden.
“The nice thing about these combinations is that if one fails, you can just swap out a pot,” said Sullivan. He suggests a three-container grouping with a 24-inch (60-cm) pot, an 18-inch (45-cm) pot and a 12-inch (30-cm) pot.
Succulents: Succulents remain popular for their shapes, colours, low cost and ease of care. Tender succulents work well outdoors during the growing season and free you of the regular watering regime.
If you are transferring indoor succulents to life outdoors, don’t put them directly in full sunlight. They need some period of adjustment to the light levels to avoid scorching, and I would give the same treatment to newly bought succulents, which may have been raised in shaded greenhouses. Move them into brighter areas gradually, if at all. If you don’t have full sun, that’s OK; they will do fine in partial shade. They will sulk and stretch in full shade.
CHOOSING A CONTAINER
The pot size drives the quantity of plants in the composition, but it also has a direct bearing on how well they do. The larger the pot, the less stress is placed on the plants; soil temperatures are cooler, the soil dries out more slowly, and roots can go deeper. The downside to large pots is that they are heavy, so assemble them where they will remain for the season. They can also devour large quantities of soil mix.
Containers that are not freezeproof, such as most terracotta pots, will have to be brought indoors before winter.
Metal pots or outer containers can get too hot for plants in the summer, especially if they are dark hued.
Otherwise, the material of the pots is purely a function of your esthetics and cost.
It is essential that pots drain to avoid rotting roots. Check to see that a pot has an adequate drainage hole, and do not place an outdoor pot on a saucer.
WATERING
Pots are best irrigated with a watering can, in which you can add soluble feed, or with a wand attached to a hose. Don’t use a regular hose nozzle, which will either dislodge soil from the pot or, if used as a fine mist, be ineffectual or even harmful. To minimize fungal diseases, water at the base of the plant, and try to avoid getting leaves wet.
If you leave an inch (2.5 cm) of space between the soil line and the lip of the pot, you can irrigate the container until the water level rises to the edge before soaking through to the bottom. That way, you know that every plant in the pot is getting watered and that the soil is fully saturated.
By late summer, the root systems can clog a drainage hole.
SOIL
Correct soil is essential to success. Do not use pot soil left over from last year, which is compacted, full of fertilizer salts and possibly diseased. Do not use soil from the garden. Do not use bags of topsoil or seed-starting mix. Use freshly purchased potting soil. Potting soil typically consists of a mix of organic matter, peat moss and perlite. Many branded mixes also contain slow-release fertilizer, either synthetic or organic.
To save money on filling large and deep pots, many gardeners will fill the bottom third or half of the container with foam peanuts or other inert bulk material. Dan Benarcik, a Pennsylvania-based container-garden expert, advises against it. The fillers take away soil that the plants need and can make the container top-heavy, a problem in summer storms. Instead, he fills the bottom half of containers with compost.
Pot shards or gravel beneath the soil may help drainage but are not necessary if your growing medium is correct. Succulents need extra amendments to the potting soil for drainage. If you can find it, chicken grit is excellent; otherwise, use builder’s sand and perlite. Mulch with gravel or grit.
PLANTING
The root systems of new plants should be teased open to encourage deep rooting, but use your hands, and be gentle; many young annuals have delicate root systems. After planting and watering, the surrounding soil may have receded. Check and add new soil if necessary to prevent root exposure. Then add a shallow mulch layer to retain moisture. I like to use pea gravel.
By September and after weeks of pleasure, the effort expended in planting your containers will be but a memory.