Sometimes the long-distance gardener looks out the window and notices that the maple tree he planted as a 6-foot sapling 21 years ago has become a shade tree 25 feet tall and 20 feet across.

Maturity creeps up on you — in trees, in the garden, in life. Year to year, the changes seem slight; cumulatively, they are enormous.

The same might be said of the world of gardening itself.

In conversation with another horticultural scribe, Margaret Roach, it turns out that she too has thought a lot about the journey through the garden’s fourth dimension: time. Over several decades, we have seen marked shifts in plant palettes, tastes and, most importantly, philosophies.

Since the 1990s, for example, we have turned from ornamental to ecologically minded gardening — to landscapes in which native plants play a larger role and gardeners seek to provide refuge and sustenance to pollinating insects and other wildlife. Despite this movement, the world of gardening has never been more multifaceted, with positive trends in passions for succulents, houseplants, tropicals, organic growing and heirloom vegetables.

Weather and climate patterns have changed too, along with pests and diseases that have materially altered what we grow. Ornamental plants once considered vigorous and flattering of the gardener turned out to be thugs or wild invaders.

Another transformation is how a longtime gardener has changed over the years. This is an interior evolution, inherently veiled, perhaps even to oneself.

Plants that were trendy at the time have become old hat or disappeared. Whither the Japanese snowbell tree or the Arnold Promise witch hazel or sedum Autumn Joy?

Roach thinks of the “it” plants she excitedly installed that would not be welcomed today.

The houttuynia Chameleon, a leafy ground cover, is impossible to remove, much like equisetum, and both go wild in wet soils. She planted lamiastrum as a ground cover; it also doesn’t know where to stop. The doublefile viburnum, from China, was once considered the choicest of all viburnums but now is showing up in natural areas and on invasive plant blacklists.

Roach is singularly well placed to reflect on these changes.

Twenty-one years ago she wrote a book, “A Way to Garden,” that combined practical aspects of gardening with its more metaphysical rewards. Her laboratory was her 2-plus-acre property in the Hudson Valley, north of New York. At the time, she also had a high-pressure post in the New York publishing world, as editorial director of Martha Stewart Living magazine.

Roach left that behind 11 years ago, decamped full time to her garden and has developed “A Way to Garden” as a brand of sorts, with a website, blog and radio show. She has revamped her book, and its reworking inevitably tracks the changes in her gardening outlook.

She painted herself as a neophyte when the first edition came out, but in her examination of the temporal space between the old and new, Roach illustrates that gardening is a journey and not a destination. It is something you do and something you live, not something you have.

When I asked her about her formative years, I could see a mirror image of myself in her pained experiences.

The 1980s and 1990s were decades when books and glossy magazines trumpeted the English herbaceous border — color-coordinated, very photogenic and impossibly demanding. Young, driven to perfection and wanting to make a mark, we were too impatient for effect, not sufficiently comprehending the purpose of gardening, and inevitably way too hard on ourselves when things flopped.

“I would run up here from the city at weekends,” Roach said. “I had to do this, I had to do that, and it was never good enough. I could barely walk up the stairs after a day’s gardening. Nothing ever looked like the beautiful pictures in the garden books of the day.”

Now her expanse of lawn, at its edges, is allowed to revert to a meadow, and Roach finds delight in simple chores and observations, such as finding a caterpillar disguised as a twig. And she loves to weed.

“I have my best thoughts weeding,” she told me, “and I know their biology. I like that I would never (have) thought I would be a girl who loves knowing her weeds by name, but I do.”

The other aspect of Roach’s gardening story is that she made a conscious decision to walk away from a high-pressure career and reset everything.

“When I was in my early 50s, I said, ‘Margaret, you don’t know how much time you have,’?” she said. “There were some economic surprises, but other than that I haven’t had a day when I wasn’t happy to wake up and look out the window and know where I was.”