Text and photos ©Nancy J. Ondra
One of the biggest challenges of creating a new garden on a relatively flat, featureless field has been figuring out how to break up the view a bit. Partly, I wanted to create some privacy from the roads that border two sides of my lot. I also wanted to add some screening within the garden, so the whole thing wasn’t visible from one spot, and to create some sheltered sitting areas as well. I needed to find a way to screen the area under the raised porch, too, so the junk-storage space underneath wasn’t visible.
My previous garden was very small, so it wasn’t a big deal to invest in some special trellises and screens, or to have Mom build them. This place is so much larger, though, that even buying enough lumber for Mom-made structures really isn’t an option. Sizeable shrubs and trees are pretty much out of the budget too. So I’ve turned to another option: perennials that are eye-high or taller.
It’s fairly easy to find tall perennials simply by skimming catalog descriptions or checking plant tags. Over time, though, I’ve come to realize that there are specific qualities that make some perennials much better for screening than others of the same height.
Quick Growth. Tall perennials as a group require some patience for screening purposes. It often takes three to four years after planting – and sometimes even a few years longer – for them to reach their mature size: a little faster, maybe, than many shrubs, but still a fair wait unless you start with sizeable divisions and not small potted plants.
Unlike most shrubs, perennials also have a seasonal down-time. Even if you wait until early spring to do your garden cleanup, you lose all perennial screening from the time you cut the stems down until summer, at least. I don’t consider the lack of spring screening a big problem, because I’m so busy planting and weeding that I mostly can ignore cars and people going by.
Around the end of June, though, I start spending more time puttering, strolling, or sitting, so I appreciate a bit more privacy. That’s rather early to expect good screening from most tall perennials, but there are a few that I’ve found reach a respectable height (about 4 feet, or taller) by mid-June. The Joe-Pye weeds (Eupatoriadelphus [Eupatorium]) are typically pretty quick to fill in, especially the giant, dark-stemmed ‘Carin’ (above), which is easily 4 feet by early summer and 6 feet by midsummer.
Above is giant fleeceflower (Persicaria polymorpha) with its new plumes poking into the 4-foot range by the middle of June. It generally reaches its full height of about 6 feet for me in early to mid-July.
Below is one of my most favorite all-around perennials: feather reed grass (Calamagrostis x acutiflora ‘Stricta’). This picture is from August, but it’s essentially the same full height of about 5 feet at flowering time in mid- to late June: a little low for privacy but lovely for lightly screening sitting areas.
Dense Habit. The density of a perennial from bottom to top also affects how useful it is as a screen. As you can see in the above photo, feather reed grass isn’t all that dense, but I like the relatively uniform look. This strip is only about 1 foot wide; a wider swath gives more screening.
In this same area, I have several other perennials that haven’t worked out at all for screening, even though they get taller than the grass. One is white-flowered Japanese burnet (Sanguisorba tenuifolia ‘Alba’), shown below in mid-August. Though it easily reaches 6 feet or more, the foliage stays close to the ground, and the tops are totally see-through. I adore this plant in both foliage and flower; it’s just not a good choice for screening, in my opinion.
Another tall perennial that’s a beauty for foliage and flowers but a dud in the screening department is giant coneflower (Rudbeckia maxima). The bottom foot or two are pretty dense, but above that, it’s see-through in bloom and in seed, as shown below in mid-August.
Now, look behind the coneflower, and you’ll see a perennial that’s fantastic for screening: ‘Morning Light’ maiden grass (Miscanthus). Even with a spring root-pruning, these three clumps, roughly 18 inches apart on center, have formed a dense visual barrier to about 6 feet tall by mid-August.
Right across the path from that combo is another great screening perennial: frost grass (Spodiopogon sibiricus). It holds its leaf blades at a wide angle from the stem, so they’re more horizontal than vertical, creating a solid mass of foliage up to about 4 feet, and the relatively airy but numerous flower plumes add another foot or so by mid-August. This beauty holds up well through the fall, too.
|Spodiopogon sibiricus in late August||Spodiopogon sibiricus in mid-October|
White snakeroot (Ageratina aromatica [Eupatorium aromaticum]) has also proven to be a good option for dense screening from crown to tip. It’s shown below in full bloom at about 6 feet tall in mid-September of 2005. (On the down side, this plant is also a prolific self-sower.)
Sturdiness. Ah, now we come to one of the big challenges of growing tall perennials: keeping them upright. It’s no good having a perennial that grows quickly and makes a nice, dense summer screen if it’s going to flop everywhere by the end of the season. That snakeroot above, for instance, is one that can readily split or sprawl if it’s in a windy spot.
My property is wide open to winds, and there isn’t much I can do about that, but the fact that I rarely fertilize or water does help to encourage stronger (though somewhat shorter) stems. As far as I’m concerned, staking isn’t an option: If you’re going to have to stake perennials to keep them upright for a screen, you may as well put up a permanent screen or trellis and be done with the job once. Pruning (by cutting the plants back by half or so in early summer) isn’t very practical, either: the resulting plants will be denser, for sure, but they’ll also be shorter, and maybe too short to be a good screen.
The Joe-Pye weeds are usually quite dependable for staying upright without help here. Shown below are a few hybrids that seeded themselves along this fence. (I started out with selections of Eupatoriadelphus purpureus, E. maculatus, and E. dubius, but they’ve crossed so many times now I have no idea what these might be.)
I have the same situation with the various ironweeds (Vernonia) I started out with: no clue what the seedlings might be, but they’re all delightfully tall (anywhere from 5 to 8 feet for most) and reliably upright.
Most grasses, too, are good about staying upright for me, but one is truly exceptional: ‘Northwind’ switch grass (Panicum virgatum). I used to think ‘Heavy Metal’ was the best for this habit, but it’s shorter (usually 4 to 5 feet), and after a few years, it formed a wider clump that wasn’t so obviously narrowly upright. ‘Northwind’ has produced bolt-upright, 6- to 7-foot-tall shocks for going on six years now without division, and the clumps stay that way even through winter snow and ice until I cut them to the ground in March. It’s shown below in mid-July.
Durability. Even if a tall perennial has sturdy stems, it’s not much good if it starts to decline soon after flowering, if it’s prone to pest problems, or if it has to be cut back after bloom to keep it from seeding all over the place.
I love Culver’s roots (Veronicastum) for their summer height and spiky blooms, for instance, but mine tend to start dropping their leaves in late summer and are pretty much leafless by fall: nice for form but useless for screening. If the summer has been dry (pretty common around here), my Joe-Pye weeds tend to do the same thing starting a few weeks later, so their stems are pretty much bare by mid- to late September.
Here again, the warm-season grasses shine, because they just keep getting better through the late-summer through fall season. Indian grass (Sorghastrum nutans) is one that’s not a great summer screen, because its foliage mostly stays in the 3- to 4-foot range. But in August, it produces its upright flowering stems, and they make a pretty light screen. (As with the feather reed grass, planting the clumps in a wider row would produce a thicker screen.) Shown below is the selection ‘Sioux Blue’ in mid-August.
Dog fennel (Eupatorium capillifolium) is another incredibly sturdy “perennial” that performed admirably as a screening plant. I put perennial in quotes because dog fennel tends to perform like an annual for me, even though it’s apparently supposed to be hardy much farther north than Pennsylvania.
Maybe I should consider myself lucky: I’ve read that it can be both aggressive and invasive in mild climates. But oh, those strongly upright shoots and feathery, bright green leaves sure were pretty. I ended up trimming out their tips when they reached the front-porch railing (about 7 feet tall), so they bushed out some more than they usually would, and they looked neat well into winter. One clump is shown below in late November, behind an edging of ‘Oehme’ palm sedge (Carex muskingumensis).
The Best of the Best. If I had to choose just one genus of perennials for screening, it would have to be the switch grasses (Panicum). I’ve already mentioned a few selections of P. virgatum – ‘Heavy Metal’ and ‘Northwind’ – but there are lots of others I like. One particular favorite is ‘Cloud Nine’, with its V-shaped habit and 7-foot height. The airy tops catch the slightest breeze, so they are almost constantly swaying and rustling. You can just see the pinkish tops of it at the end of the path shown below.
Below is ‘Cloud Nine’ about a month later (in October), towering above ‘Cassian’ fountain grass (Pennisetum alopecuroides).
An even-more-favorite favorite of mine is ‘Dallas Blues’, because its powder blue, wider-than-usual leaf blades and pink flower plumes are so distinctive.
I have a corner of the front garden planted with a half-dozen of these to create an almost-secret sitting area. Even though I’m only about 30 feet from the road there, the density, movement, and swishing sound of the plants as they move in the wind block a good deal of the noise from passers-by. It grows fast, it’s sturdy, it’s durable, and it’s dependable: exactly what I’m looking for in a screening perennial.
|Panicum virgatum ‘Dallas Blues’ in late August||Panicum virgatum ‘Dallas Blues’ in late October|