“Plants have a pre-programmed height that they grow to.”

This sugar maple might someday top out at fifty feet. Or seventy-five.

Not for one second. It’s surprising the number of encounters I have with gardeners who say something along the lines, “They told me at the nursery that such-and-such viburnum would grow eight feet tall, and last year it hit ten.” Ah yes. It hasn’t stopped growing yet. And won’t until it dies.

“Mature” height figures given for plants are averages, based on observation of the plants grown over their lifetimes. Will a Black Hills Spruce really stop growing once it hits forty feet? Yes—if, within five or six years of hitting forty feet, it dies, it will. If it was planted in a particularly groovy spot, it happened to love its soil, it was well cared for early in its life, and it now rolls on into its sixth or seventh decade having never caught a bad case of fungal disease, it may hit forty-five or even fifty feet. But the average maximum height will be forty.

That’s all any of these height values are based on. They are a bit more accurate and meaningful when it comes to perennials. Veronica ‘Royal Candles’ may top out at seventeen inches in Zone 4, twenty inches in Zone 6, but it’s not going to magically hit three feet if you grow it in the deep south.

But be aware, there are reasons why something like a pyramidal arborvitae (Thuja occidentalis ‘Pyramidalis’) is listed in catalogs with a height range of 12-25’. Some people will see them die in fifteen years, at somewhere around twelve feet tall. Others may enjoy the plant for decade after decade, and live to see it hit twenty-five. Depends on the gardener.

“Annuals bloom all summer long”

Raise your hand if you’ve ever read this line in a garden magazine article about planning and planting a perennial garden: “And don’t forget to include pockets of annuals, for season-long color.”

It’s a myth. Even in Minnesota, which has a gardening season of May through mid-October (if we’re lucky), I can’t think of very many annuals that will look good and deliver blooms across our entire six, six-and-a-half month growing season. A sternly pinched coleus, perhaps, or impatiens in the shade.  For those of you in places like Nebraska and Missouri, Georgia and Texas, well, come on.

You’re not a bad gardener because the annuals you planted in April or May look like hell by mid-August (or the 4th of July). You’re simply learning that the gardening industry tells the odd fib. Deadhead your annuals, learn which ones will take a good mid-season shearing, but when they stop blooming and start drooping, rip them out and plant fresh ones.

“Trees should be watered every two days after planting”

Or every day, or three times a week, or all sort of times that will, quite quickly, kill the tree.

Just when I think I’ll run out of myths—there are an awful lot of them if you click the Archives below—several times a season I’ll run into homeowners who provide fresh fodder for my cannon.

This was the myth I heard several times this summer, earnest homeowners who had heard, from someone somewhere, that a tree needs to be watered every two days for about a month after planting.

Unless you’ve planted a palm in sand, that’s way too much water. When you plant a tree, water it well at time of planting, then water it every five days. This is assuming that your soil drains to some reasonable degree. How much water? Five gallons for a small, potted tree, evergreen or deciduous, ten gallons for a mid-sized tree, and fifteen gallons for large, B&B specimens. How do you know how long it takes to deliver five, ten, or fifteen gallons to the ground around the tree?

Acquire a five-gallon pail. Fill it to the brim from your hose, and time how long this takes. Now you know how long it takes to deliver five gallons of water from your hose, at whatever rate you set by turning the handle, from a gentle trickle to full bore.