Almost every planter sold online is listed by one number, and it is the wrong one. The width you are reading is measured across the widest part of the body. The number that decides whether your plant goes in is the opening, and on a jar those two can be eighteen inches apart.
The same piece measures nearly forty inches across the body and about half that at the mouth. Restaged from the maker's photograph.
The first number is not the opening
Pottery is measured across its widest point, which on a straight-sided pot is roughly the same as the mouth and on a jar is nothing like it. The shoulders draw in above the belly, so a piece that reads as enormous in the listing can have an opening little more than half its stated width.
This is not a trick anyone is playing. It is simply the convention the trade measures by, and it catches people out constantly because the second measurement usually is not published at all. Across the thirty-nine planters we carry, the maker states a true inside diameter for four of them. For the rest we would rather say so than print a number we cannot stand behind.
The example above is real and it is the most extreme in the range. The same planter is listed at 39.5 inches wide, and the mouth is 21. A mature boxwood on a 24-inch root ball does not go into it, and no amount of reading the listing carefully would have told you that.
Start from the root ball, not the plant
If the piece is a living plant, the root ball is the constraint, and it is a fixed object. The commonest size on our mature live boxwood is a 24-inch ball; smaller pieces come on 18, and the largest specimens on 36. It is listed on the pieces where we publish it, and we will tell you for any piece where we do not.
The ball has to pass through the opening with room around it for planting mix, so the working rule is straightforward:
Opening ≥ root ball + 4 inches. A 24-inch ball wants a 28-inch opening or better. At exactly the ball’s diameter you cannot get mix around the sides, and the plant sits in a collar of air that dries out and kills roots at the edge.
Artificial and preserved pieces are easier, because there is no root ball at all: they arrive on a spike, a base or a small starter pot, and the only question is whether the base is hidden and the piece is held steady. That job is a different one, and it is covered in planting artificial topiary in pots.
Proportion: how tall a plant suits which planter
Once it fits, the question is whether it looks right. The rule we use, and it holds up remarkably well, is that a planted piece looks settled when the plant stands about one and a half times the height of the container.
Much shorter than that and the pot takes over. Much taller and the whole thing reads as top-heavy, which is a real problem in an exposed position and not only a visual one.
| Planter height | Plant that suits it | Finished object |
|---|---|---|
| 18 in | about 27 in | 3 ft 9 in |
| 24 in | about 36 in | 5 ft |
| 30 in | about 45 in | 6 ft 3 in |
| 39 in | about 58 in | 8 ft 1 in |
Add the two together before you decide, and measure the doorway or the soffit it has to live under. Topiary height itself is quoted from the soil line, not from the bottom of the container, which is explained in how we measure a topiary.
Some planters are better standing empty
Several of the tallest pieces we carry are 44 to 49 inches high. By the rule above, filling one properly needs a plant of five and a half to six feet, and the finished object is over eight feet. In most gardens that is not what the position wants.
A tall jar holds a corner perfectly well on its own, and treating it as sculpture rather than as a container is often the better answer. If you do plant one, plant it low and wide rather than tall: a single ball at the mouth reads far better than a standard that pushes the whole thing over eight feet.
Weight, wind and the ground underneath
Size decides two practical things besides fit. A large glazed planter with wet mix and a mature plant in it is a several-hundred-pound object once planted, so it is sited before it is filled, never after. And a tall narrow piece with a heavy head on top is the arrangement most likely to go over in a gale, which is another argument for the wide, low containers when the position is exposed.
Fibreglass is the exception on weight and is considerably lighter than it looks, which is what makes it the practical choice on a roof terrace or a balcony. What each material does to the plant, and to your back, is covered in planter materials for live plants.
If you want us to check
Tell us the piece you intend to plant and the planter you are looking at, and we will measure the opening before you order rather than estimate it. That offer is the honest version of a specification we cannot publish for all thirty-nine, and it costs you nothing.
The range is on the planters pages, and the plants that go in them are on live boxwood topiary.
