The seed packet says fresh basil; the garden center sells a large container to hold it in: a big pot, maybe a ceramic one. You start a little plug of seedling inside it, water it, and wait. Days go by. So does the water. The soil doesn’t dry out. So what’s wrong? Why isn’t the basil growing bigger?
It’s a trap. Bigger isn’t necessarily better. In fact, too-large containers can be trouble because there’s a mismatch here: between volume and root mass. That’s not the problem with your soil, or even how much you’re watering. It eliminates the who-knows-what-diameter-each-pot-is confusion common with gallons-only lists.
Think Small and Grow Step by Step
Four inches are perfect for a tiny succulent or herb whose root system fits inside it. Roots rot if they sits in sodden soil in a big pot that has too much moisture for its little roots. Bigger things get bigger; they require more room as time passes, but a palace isn’t what they want. Six-inchers work well for chard, for instance, and lettuce. Their shallow root systems prefers the width, not the height. You’re paying for wasted empty space when you place a six-inch-wide clump of lettuce in a twelve-inch pot filled with excess water.
Then there’s the matter of fruits. Dense-rooted, aggressive feeders like tomatoes, eggplants, and peppers want wide, deep spaces to yield heavily. A dozen inches is ideal for indeterminate eggplants and tomatoes; that’s roughly the diameter of a five-gallon container. It offer the water buffer they want on a hot day. Otherwise, they’re quick to shrivel, stressing them to drop blossoms or produce ugly-looking fruit. Dwarf varieties of citrus and blueberries requires even bigger spaces, such as a 14-inch pot or larger. This allows their long root systems to stretch out and helps protect them from wild temperature fluctuations.
The most important thing is the lesson of transitions. We jump the gun, as gardeners do, and take a plant right out of its nursery cell and put it into a big pot, leaving a wasteland of unused soil all around the little rootball. If environment isn’t hospitable, there’s no reason for roots to stretch out into nothingness. Too much moisture in the empty soil will cook the roots you already have.
Up-pot gradually, instead. Move from a four-inch pot to a six, and then up to an eight. Each increase challenge the roots to fill more territory. When they wrap around the base, go up again. The result: a full, compact root system.
Wide is not everything. For shallow-rooted plants like herbs, a pot that is wide but shallow (like the one below) will be a waste of space. Its base will stay soggy, which roots do not go into or dry out. Too small for something with deeper roots, like tomatoes, a shallow container dries too fast. Fit the shape to root system. And remember: If you can’t get water OUT, what’s the point? Good diameter won’t help if there’s no drainage. Pots must have open drainage holes. Plan on leaving about an inch of empty space above the surface, so they won’t overflow when watering settles.
Restraint is the key to successful container gardening: Think small. Upsize gradually. Give them time to fill out what they’re in and then give them more space for their roots to grow. You should of given them time. Stronger plant equals stronger growth equals higher yield. Instead of a pot full of mistakes from over-watering, you have a productive garden on your patio. Actually, it’s better than just having any plant. A luxurios garden is the goal.