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Every gardener dreads seeing them—those gaping bare patches where thriving plants once grew. Sure, gaps can be problems in block style planting where many plants are planted together. While I thought my matrix-style planting approach would protect me from this common problem, I'm now staring at my first significant hole. It’s about 5 feet by 5 feet (header image).
What used to be here? As I mentioned a few weeks ago, I’ve lost Pycnathemum tenuifolium (narrow-leaf mountain mint) in the beds near the house. I’ve gone from it being a very dominant plant in the seasonal layer just a few years ago to it being virtually absent.
The clumps used to be so thick they’d appear as dense sheets of rhizomes in winter. But, I’ve been pulling stems out by the handful this summer. Pycnanthemum is not typically a species that has a groundcover layer underneath, so when it’s gone, bare soil is left behind.
A photo from 6 years ago showing how dense the Pycnanthemum tenuifolium (narrow-leaf mountain mint) was in the garden.
I’ve been pondering why I’ve lost them in the hopes I can replace this species one day.
Has the soil acidity started to shift back to more acidic? I’m going to do a soil test on this area to see.
Have things started to dry out too much for it? Nah, we’ve had one of the wettest years I can remember. Plus, I know Pycnanthemum can grow in gravel gardens and green roofs.
Are voles to blame? Why eat mountain mint, something that anecdotally they tend to avoid and not the Echinacea mere feet away?
Has disease wiped it out? Perhaps, but small rhizomes that I found and potted up have good new life.
These why questions are one thing, but more important is if a species doesn’t work anymore, what do we do?
We need to identify suitable replacements. The desire to try something new after a gap appears in the garden is always a strong urge for a gardener, but in this style of planting, too much diversity can make things look disjointed.
I’m looking at the rest of the garden for inspiration and thinking of something that will offer long season interest. If there are plants already thriving in this space, that means they will likely help patch this hole.
The autumn flowers of Boltonia diffusa (southern doll’s daisy)
I added Boltonia diffusa (southern doll’s daisy) to these beds last year, and they have looked stellar this fall. They have fine foliage in the spring, and they turn into a haze of white flowers come late summer and autumn. This plant would be a great contender for the hole as I’ve already been asking how can I have more of this species. For the spring, Phlox pilosa ‘Bonnie’s Pink’ provides good color. I can interplant the Phlox and Boltonia together, and the Phlox will go dormant in the summer before the Boltonia comes into flower.
Conoclinium coelestinum (mist flower) has also provided good color this fall.
Fortunately, the disappearance of the mountain mint in the other beds is less evident. Rhizomatous Conoclinium coelestinum (mist flower) that I initially regretted planting for its aggressiveness has filled the spaces where the Pycnanthemum originally was. That ultimately is one of the goals of this style of planting, to heal gaps as they occur. And, my mindset on mist flower has changed. One lesson I’ve learned in Texas is that sometimes you have to celebrate the plants that can live here no matter what.
If you’re dealing with similar issues, remember those gaping bare patches don't have to be garden failures. They can be great opportunities for the garden to evolve.
Conoclinium coelestinum and Boltonia diffusa (back) provide color in the garden in autumn.