Sorry we let you down.

This one isn't by Henry Mitchell, but I wonder if it's the one you have been looking for? (Click on link.)

Here is a link that might be useful: Why I Garden

Excerpt from
Henry Mitchell on Gardening
By Henry Mitchell

When you first start to garden you usually have no idea what the real delights are going to be. You generally suppose the joy will come from raising the first dahlia bigger than a washtub or producing a rose seven inches across. These are heady highs, of course. But they overlook the element of time. Time, you might almost say, is what gardening is about.

It's one thing--and a fine one--to see the leaves fall in November and the first crocus in January and the snowdrops on February 4 and the azaleas on April 15 and so on and on, the first year you see all this.

It's another and more resonant thing the thirtieth time you see it. A certain daffodil opens on March 4, and you are dumbfounded. Always before it opened on March 15 or 16, not varying year after year. So why is it blooming so much earlier this year? The weather and temperatures give no clue. Now this makes the flower much more engaging than it would be had you not watched it opening on March 15 for the last twenty years.

The roses come and go. At first you think, when June comes and the bush is out of bloom, that an eternity will pass before next May when it blooms again. But after a few years you conclude that 'Agnes', say, is worth growing even if it blooms once a year.

It is very like discovering that youth does not last or come around on schedule every year. At first it is a shock. But if you are reasonably lucky, as I was, you like getting older. You don't have to live through all that youthful bother again, and the future may well be novel and more agreeable than the past.