If horticulture has a fine art, growing plants in containers would be it. Plants in containers are completely dependent on us. The health of a container-grown plant is an indication of the care lavished upon it and the knowledge of its human helper.
A plant may be kept in a container for hundreds of years. This is evidenced in the Japanese art of bonsai, and in the potted orange trees at the Palace of Versailles near Paris, some of which were planted in the 18th century.
Succulent plants, especially, lend themselves to container growing. Their roots are shallow so they take a long time to fill the container in which they grow; their leaves hold moisture tightly so they can survive without water for long stretches of time.
You can grow virtually any species of plant in a 15-gallon container for years as long as you remove it periodically and prune its roots. You can tell a plant is ready to be root pruned when its leafy growth begins to decline. That’s generally a sign that roots are circling the inside of the container. In the worst case, when water is applied, it does not seep into the soil but, due to the congestion of the roots, migrates to the edges of the rootball (block of soil in which roots grow). Until you get around to root pruning, use ice cubes to water instead of a hose; water from the melting cubes will go directly into the soil below.
Root pruning involves cutting away one-third of a plant’s rootball. Cut equal portions off rootball sides and bottom. Put fresh soil back into the container, place the pared-down root ball in its center, and then fill in more soil on the sides. Such root pruning is advised for fast-growing Ficus trees, for example, whose leaves turn yellow and begin to fall when roots start to circle and cluster inside the container. This state of affairs is known as a root-bound or pot-bound condition.
Enter the grow bag, which is defined as you might think it would be: a bag where you grow plants. Consider a plastic bag full of potting soil, available at any nursery, to be the most basic example of this. Lay your bag of potting soil or soil mix on its side in your yard or garden and cut out a large window, just a little bit inside the perimeter of the bag. Take a screwdriver and punch holes in the bottom of the elongated bag for drainage. Then plant your seeds or plants procured in six-packs, three-inch or four-inch containers directly into the soil in the bag. This is the ideal setting for first-time gardeners since plants inserted into such a rich soil mix will undoubtedly grow well.
More sophisticated grow bags would be repurposed grocery shopping bags made of jute or other fabric. The advantage of fabric bags is that they prevent development of a root-bound condition. The case for such grow bags is made in a new book entitled “Grow Bag Gardening” (Quarto Publishing, 2021) by Kevin Espiritu.
“If plants could talk and you asked them how they felt about being grown in containers, there’s a good chance you’d hear them whine and grumble about it. They’re used to growing in the ground, where they evolved and adapted to grow for millions of years,” Espiritu writes.
“When a plant’s root system reaches the edge of a common plastic or terra cotta pot, it . . . continues to grow – but there’s nowhere for it to go. Instead of growing out farther, it starts to circle around the pot, eventually forming a pot-shaped rootball. . . By slicing off circling roots . . . a plant can be given another shot at a productive life,” but “you also run the risk of damaging the plant beyond its ability to recover.
“Due to the porosity of the material used to make grow bags,” the author continues, “plants grown in them don’t suffer the same fate as traditional container plants. When a plant’s roots reach the end of a grow bag, those roots encounter an air-rich environment that is low in water and nutrients. This causes the tips of the roots to die, signaling the plant to produce new roots elsewhere in the root system.”
As far as grow bag options are concerned, you can always purchase them ready-made from Internet vendors, but burlap sacks are also suitable for this purpose. You can also sew your own from landscape fabric, that perforated material laid down on bare ground prior to planting in order to prevent weeds.
Regardless of whether you use conventional containers or grow bags, leaving them unattended during one hot Los Angeles weekend could result in severe plant stress or even death. You could, of course, install a drip system so that no water deprivation of your containerized specimens would occur. Where that is not practical, place each container inside a larger one and fill the gap between them with wet peat moss. The rootball in each container will be insulated from the heat by the moist and cool peat moss in the container outside it.
Container plants need a constant supply of fertilizer, especially those growing in full sun, where watering is frequent. Throughout the growing season, a weekly dose of any complete liquid fertilizer (with nitrogen, phosphorus, and potassium) is suitable for evergreen flowering plants such as bougainvillea and hibiscus. In addition, a slow-release fertilizer such as Osmocote should also be used topically throughout the year. When the slow-release pellets disappear, just add more.
During spring and summer, container plants must be kept constantly growing. Any stagnation in growth may result in loss of leaf color, decline in flower production, disease and insect problems. This does not mean growth must be rapid, just kept steady.
Often, container plants are placed where they do not get sun equally on all four sides. To prevent plants from leaning in one direction, rotate them 90 degrees (a quarter turn) on a weekly basis.
There is nothing more exhilarating than the sight of a glorious plant suddenly popping up where you didn’t plant it. Years ago, I installed a trailing lantana variety with lemon-colored flowers in my parkway. Lantana blooms virtually non-stop and does not need water once it is established. Suddenly last spring I noticed a few freeway daisy (Osteospermum fruticosum) flowers poking up through the lantana. This year, the freeway daisy has gained in strength. Its blindingly white flowers perfectly complement the lantana’s golden blooms and lush foliage. Freeway daisy is known to self-sow and I can only surmise that its seeds must have laid dormant in this spot for years but only now found that the conditions were right to germinate. Although freeway daisy is classified as a perennial, it typically lives for only a few years before succumbing to root rot. But for those few years, what joy!
Tip of the Week: Daisies are the harbingers of spring. Shasta daisies are long-stemmed classics that grow in clumps in full to partial sun and will inhabit your garden for years, serving admirably in cut flower arrangements. Marguerite daisies (Chrysanthemum frutescens) bloom in three-foot mounds of pink, sulfur yellow and white, while ‘Ruby Slippers’ shows off carmine-red blooms. If flowers are regularly removed as soon as they fade, you will see several waves of bloom throughout the year.
And once you’ve seen it, the Santa Barbara daisy (Erigeron karvinskianus) is hard to live without. Picture a proliferating mound that spreads or spills or drapes down and around and is covered with probably a thousand miniature pinkish-white daisies. The Santa Barbara daisy, native to Mexico and Central America, is meant not only for sunny garden, block wall, or walkway border planting, but tolerates a fair dose of shade as well as poor soil and drought. It is eminently suitable for patio and balcony planters and hanging baskets as well.