A visit to the Pacific Northwest makes me pine for acid-loving plants—Japanese maples, azaleas and rhododendrons, to name a few. But I live here in Colorado, where the soil is often highly alkaline. Our pH runs over 8, much too high for many landscape plants popular in Oregon, Washington, and other areas with high rainfall and acidic soil.
If you read articles written for northeastern gardeners, you may get the impression that pH is easy to fix. Too low? Add lime. Too high? Just add sulphur (or aluminum sulfate), peat moss, or sawdust. The only problem is that throughout much of the arid West, our soils are alkaline because of their high calcium content. We’re gardening on decomposed limestone, and no amount of amending is going to fix that.
(If you’re unsure whether you have soil with a high pH, try adding a little vinegar to a small sample of dry soil. If it bubbles and foams, it’s alkaline.)
Instead of fighting Mother Nature, I’ve learned to embrace what I have. Since we’re stuck with the pH we have, the best approach is appreciation. There are plenty of gorgeous plants that actually prefer a higher pH. I see them all around me—Honeylocust and green ash trees, Japanese barberry, junipers, and lilacs, honeysuckles and clematis. I could spend pages listing them all.
Most urban yards only have space for a few trees, perhaps a few more shrubs or vines, and a patch of lawn. But what brings the most joy to my gardener’s heart isn’t a perfect lawn or bulky shrubs. It’s the flowers. What I really want to know is, what perennials can I grow with my alkaline soil?
At first, I was concerned that once I eliminated all the perennials that can’t withstand my zone 4 winters, that hate harsh, drying winds, summer hail, torrential downpours and persistent drought—and then added a filter for those that thrive in soil with a pH over 8—there wouldn’t be anything left.
I needn’t have worried. There are more than enough to choose from—sun lovers and shade lovers, low-growing edging and tall background plants, in every color imaginable. Here is a far-from-comprehensive list gleaned from a number of websites. For those I’ve previously written about, I’ve provided links to those posts. All of these are perennials suitable for Front Range gardens, although some are less xeric than others.
Perennials for Colorado’s Alkaline Soils
- Achillea – Yarrow
- Anchusa azurea – Italian Bugloss
- Aquilegia – Columbine
- Brunnera – Bugloss
- Centaurea montana – Mountain Bluet
- Digitalis – Foxglove
- Echinacea – Coneflowers
- Geranium – Hardy geranium
- Helleborus – Lenten rose
- Hemerocallis – Daylilies
- Heuchera – Coral Bells
- Hylotelephium – ‘Autumn Joy’ Showy Stonecrop (aka Sedum)
- Iberis sempervirens – Candytuft
- Iris – Bearded iris, Reticulated Iris
- Kniphofia – Red hot poker
- Lavandula – Lavender
- Leucanthemum × superbum – Shasta daisy
- Lilium – Lilies
- Lychnis chalcedonica – Maltese cross (photo at top of post)
- Nepeta × faassenii – Catmint
- Papaver – Poppy
- Phlox – Creeping Phlox, Garden Phlox
- Polemonium caeruleum – Jacob’s ladder
- Pulsatilla vulgaris – Pasque flower
- Rudbeckia – Black-eyed Susan & Gloriosa daisy
- Scabiosa – Pincushion Flower
- Sempervivum tectorum – Hens and chicks
- Solidago – Goldenrod
Photos, from top and clockwise: Maltese Cross (Lychnis chalcedonica); Columbine (Aquilegia), Catmint (Nepeta x faassenii), Oriental Poppy (Papaver orientale), Hardy Geranium; Astilbe, Italian Bugloss (Anchusa azurea); Japanese barberry, Clematis, Honeysuckle (Lonicera); Mountain Bluet (Centaurea montana), Red Hot Poker (Kniphofia), Daylily (Hemerocallis), Candytuft (Iberis sempervirens); Easter Lilies, Shasta Daisies (Leucathemum x superbum).