Learn from Marylee's mistake: This pistache tree needed to be replanted in less than a year, even though it was in an RPB.

One gardener’s “really big pot” is another gardener’s medium-sized pot—at best. I often chuckle when I ask someone, “What size pot do you have?” and the person responds that a “really big pot” is 18 inches in diameter.

“Really big pots”—aka RBPs—are, in my book, pots that are at least 32 inches in diameter—and we must plant in large pots, no smaller than 20 inches, in order to have successful full-sun potted gardens in our desert heat. The soil volume in these larger pots gives the roots a fighting chance to keep their cool.

Since RBPs obviously take up a lot of space, you want to think about using RBPs where they can serve a specific function in your exterior design. They might become a focal point—with or without a plant. They might break up the monotony of a large flat wall, or if they include a vine, shrub or small tree, they can hide an eyesore—and even provide screening from your nosy neighbors.

Your best bet when planting in super-sized pots is to choose plants that you will either replace each year—like annual flowers—or plants that are slow-growing. Most nursery plant tags will say what the rate of growth is for a particular plant—and pay attention! I once made the mistake of planting evergreen pistache trees in 32-inch pots. Those trees, with the love and care of regular water and food, outgrew the pots in less than a year. The trees were not overly large—but the root system could not grow large enough in the pots to support their canopy.

Here are some basic tips on how to handle RBPs.

1. Make a firm decision as to where you want the pot placed before planting in it. Have you ever tried to lift a 22-inch container garden filled with dirt and plants? I have—and it was overwhelmingly heavy. Once planted, an RBP will be virtually impossible to move. To do so will require that you empty it of all the plants and soil. Be sure!

2. If you know you are planting shallow- or medium-rooted plants in an RBP, do not fill the entire pot with soil. If you are planting small perennials or annuals, you can fill the lower two-thirds of the pot with other material. When planting a small shrub-type plant, you need more soil volume, but you can fill the bottom third with nonorganic material. (Do NOT use rocks; they just make the pot heavier!) I recommend that you cover whatever material you use with a sheet of landscape fabric. This will allow water to go through, yet will help maintain the soil above the fillers. Filler possibilities include a larger-sized terra cotta pot that you do not care about, upside-down at the bottom of the pot; upside-down black plastic nursery pots (squeezing them to fill in as much space as possible); used six-packs or nursery pots, or even packing “peanuts,” bundled inside a leaf bag; empty plastic bottles or aluminum pop cans, covered with landscape cloth; or even plastic foam, broken into manageable pieces. Whatever you do, make sure you do not seal the drainage hole shut.

3. Do not fill your pot with soil from your garden—even if your garden has the very best soil on the planet. Garden soil is heavy and “dirty” (replete with weed seeds, bugs and their eggs, bacteria—stuff that you don’t want in your pots). Instead, use a good potting soil (also called potting mix or container mix). Potting soil is well-aerated, sterile, lightweight and made of a good balance of organic material and mineral particles like peat, sand or perlite. (Potting soil is actually soilless—that is, it doesn’t contain any dirt.) When choosing a potting soil, it should smell and feel rich. It will not be sandy or smell like manure.

4. When planting a tree in an RBP, fill the pot completely full with soil. Trees also need to be planted in solidly based pots in order to reduce the tipping factor. The base of the pot should be almost as large as the top of the pot. Our desert winds have been known to blow over many pots—even super-sized ones!

5. If you put a large plant in an RBP, you do not need to change out all of the soil every few years, like you do in smaller pots. Instead, each year, remove a top layer of old soil and add new soil, along with time-release fertilizer. Mix it in with the old soil as much as you can without severely disturbing the root system. Keep the soil level at the same depth as before, so you don’t cover the root or trunk any deeper than it was originally planted.

By following these methods, you can enjoy terrific potted gardens for many, many years!

Marylee is the Desert’s Potted Garden Expert. Email her with comments and questions at potteddesert@gmail.com, and follow the Potted Desert on Facebook. Her column appears every Tuesday at CVIndependent.com.

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