Before You Buy a Single Plant This Spring: Read This!
Plus: Why you need to stop filling the bottom of your pots with rocks
Some of us are still waiting to start a few seeds indoors.
Others are still waiting for the snow to melt before we can even begin to envision what this year’s garden might look like. And then there are container gardeners like me, staring at last season’s empty pots and wondering: what can I do differently this year to avoid some of those expensive disappointments?
Susan Martin, a horticulturist with nearly three decades of experience and Head Copywriter/author of many gardening articles for the Proven Winners website, has some answers.
Susan has run a container design business and she is the first to tell you that container gardening is not a cheap hobby. It is, however, one worth doing right.
1. DRAINAGE IS NON-NEGOTIABLE
Diana: Is drainage really the biggest beginner mistake?
Susan: Yes. And the reason I put it first is that once you’ve already filled a pot with soil and plants, you’d have to empty the whole thing out and start over if there’s no drainage. You need to know the pot has a hole before anything else goes in. Some have a pre-drilled hole with a plug, and sometimes people forget to remove it. Whatever you need to do, whether it’s drilling through ceramic with a diamond bit or punching a hole in a tin container with a nail, you need drainage.
Once a plant drowns, even just once, root rot settles in very easily in a contained environment. And once it starts, it doesn’t really stop. You’ve lost your entire investment.
2. WATERING IS AN ART FORM
If drainage is the rule you set up before planting, watering is the practice you commit to all season.
Diana: What does it take for a beginner to develop that instinct?
Susan: Be a close observer of your plants. A drooping plant does not always mean a dry plant. It could mean root rot. It could be a plant like Ligularia, which wilts in the sun to conserve moisture and then springs right back up in the evening even when the soil is perfectly moist. Stick your finger into the soil to the second knuckle. If it’s dry down there, it’s time to water. If not, leave it. More people kill plants from overwatering than underwatering. Watering and sun exposure are the two most important factors in container gardening, after drainage.
[Diana’s note: For Minnesota gardeners, Ligularia (Ligularia dentata), also called leopard plant, is a lovely choice for shady or partly sunny locations, zones 3-9.]
I learned this firsthand last summer on my east-facing Minneapolis patio. I came out one morning to find my salvia completely wilted, grabbed the hose, gave it some water and within a few hours the plant was back up.
Susan was not entirely convinced that was the right call.
Diana: So tipping the pot is your go-to test?
Susan: If it doesn’t feel heavy for its size, it’s probably dry. Stick your finger in the soil to confirm. If you’d watered recently and the plant doesn’t usually behave that way, pause before assuming under watering. You could make the problem worse.
3. THE FILLER-IN-THE-BOTTOM MYTH
The idea of putting rocks, pebbles, or old potting soil in the bottom of a container to improve drainage is one of the most persistent myths in container gardening.
Diana: What’s actually happening when people do that?
Susan: There’s physics involved that most people don’t know about. As long as the growing medium is consistent all the way down, water travels straight down and out the drainage hole. But the moment you introduce a different material, the water hits that layer and moves horizontally. It builds up, sits there, and the bottom of your container becomes a sopping wet sponge. The most sensitive part of a root is the tip. Now those tips are sitting in standing water. That’s how rot starts, and once it starts, it moves up. Old potting soil is the worst option. It’s broken down into much finer particles and water does not drain through it at all. You want to save a few dollars, but you’ve now lost the twenty-five dollars of plants in that container. It’s better to start fresh.
[Diana’s note: I’ve been told using a coffee filter works well instead of rocks or pebbles. Another suggestion is put a newspaper page down. Both will degrade over time and not interfere with roots or water pooling in the base of the container].
Susan: If a very large container comes with a false bottom built in, that’s fine. It usually sits about a foot down, which gives most annuals, including petunias, calibrachoa, and salvia, enough depth to thrive. But if I’m growing something with deep roots, a grass, a canna, a perennial, I fill the whole container to the bottom with fresh potting soil.
4. IF YOU DO ONE THING RIGHT, MAKE IT THE SOIL
Susan: Start with quality potting soil. You can put great plants in low-quality soil and still not get great results. Good potting soil is lightweight, well-drained, and fluffy. Here’s my rule: if the bag is hard to lift, it’s not good potting soil. That’s garden soil, and it does not belong in a container. Every time it rains or you water, soil in a pot gets compacted. If you don’t start with something fluffy and lightweight, you will suffocate the roots of your plants. Flowers have fine, delicate roots. They need air spaces to spread into, not dense clay.
5. BUILDING A CONTAINER: START WITH THE THRILLER
Diana: Where do you start when you’re shopping?
Susan: I always start with my Thriller. That’s usually the most unique plant in the container, the tall one, the one with the big leaves, the one that catches your eye. I build everything else around it. Pick three colors and stay within the shades of those colors. It makes shopping so much easier when you’re standing in a garden center surrounded by every color imaginable.
[Diana’s note: The Thriller/Filler/Spiller framework is the backbone of most successful container designs: Thriller, one tall dramatic plant to anchor the arrangement; Filler, mid-height plants to fill in the body; and Spiller, trailing plants to cascade over the edge and soften the container. It is a forgiving structure that works for beginners and experienced designers alike].
THE HONEST PART
I asked Susan whether there’s a container combination she returns to every year, something she counts on.
Susan: No. I like to do something different every year and I never repeat. There are literally tens of thousands of plants I haven’t tried yet. I could garden my entire life and do different containers every year and never even scratch the surface of what’s possible.
She paused.
“Life is too short. There are too many fun plants to grow.”
Susan Martin is a horticulturist and gardening writer with nearly three decades of experience. To see Susan’s article on container gardening,
follow this link.
That’s the dirt… now go grow something beautiful.
Diana
#bloomwithme
I love the tip about potting soil: if the bag is too heavy to lift, it's not the right soil. Better for the plants and better for my back! 🤣
Great article. Good enforcer of basic principles.