If you live in the Pacific Northwest, you’ve probably had the experience more than once of buying a plant that the nursery tag said would grow to the perfect size for your garden – but within a few years, it was pushing against its neighbors and becoming unruly. Why aren’t the plant tags accurate?
Well, they are mostly accurate for herbaceous perennials. That’s because most herbaceous perennials die back each year, and only have the juice to grow so big in one season. They will spread wider in time, but that’s when you divide them and enjoy a few free plants to give away to your friends.
But for shrubs, the tags are actually a five- to ten-year estimate. You see, woody shrubs don’t hit a certain size and suddenly decide not to grow any more – they continue growing. They may slow down in time, when their woody stems get old enough that they don’t let the sap flow as well as it used to – but they don’t stop.
Add to that the fact that many growers are in hotter, harsher climates which can stunt plant growth, and you’ll understand why our mild climate produces growth so far beyond what those growers estimate.
So what can you do to avoid the endless cycle of pruning and moving shrubs as they outgrow their spaces?
First, add at least 25% to whatever size the plant tag says. Imagine that your four-footer is going to be 5’ or more in 5-10 years.
Second, give your plants some room to breathe. Don’t be in a rush for a full garden – the fuller it looks when you plant it, the more you will need to prune to keep plants from sprawling on each other. If you think a plant will get to 5’ in 5-10 years, then measure out the 5’ round space where it will be (I usually draw a circle in the soil with a stick), and then give it an extra 6” to 1’ all the way around so when it is mature, there is still airflow and room to squeeze past while you are pruning and caring for your garden.
If things look bare in the beginning, you can always tuck in some short-lived plants like Columbines, Foxgloves, Canterbury Bells, Nigella/ Love-in-a-mist, Mullein/ Verbascum, Cineraria, or Forget-me-nots. They’ll either re-seed after bloom, or you can purchase small six-pack starts to plant each year in fall to fill in. That way you get the look of a full garden right away, and as your shrub grows, you can pull out seedlings that are too close to it.
Another tactic for an immediately full look is to tuck a low perennial groundcover between your shrubs, like Campanula or Dwarf Mondo Grass. Choose something that won’t get taller than 8” or so, so that when your shrub fills in, your groundcover can still hang out and add some color around its feet. Do keep a 1’ radius around each shrub’s base totally clear of anything but mulch, though – plants don’t like a lot of root competition!
Lastly, if your shrub has tiny leaves, you can probably shear it each year to keep its habit full rather than leggy. Just use your hedging shears and trim off every stem’s tip. You can even bring it in a few inches, as long as you don’t prune to bare wood – make sure there’s plenty of fleshy green growth left when you are done. This works great with Heathers, Lavenders, Hebes, Cistus/ Rock Rose, and many others. Fall is a great time to do this.
For plants with larger leaves or a woodier habit, just pinch off the growing tips each spring back to a side bud or leaf to get the same effect. Remember that plants will grow at the tips, where it is easiest for them, so if you only pinch a few stems back, the plant will keep growing from its other stems and not fill in. That means in order to do a successful job of pinching your plant to encourage a more compact habit, you’ll want to pinch off every growth tip. Just take each stem back to the closest leaf or side bud, and you’ll soon notice the buds lower down in the plant bursting forth with fresh new stems.
If you take these tips to heart, you’ll avoid much of the major pruning that makes plants look bare and out-of-proportion to their neighbors, and your garden will become easier to care for and more beautiful.