Watered Down : Too Much Moisture Is the Leading Cause of Casualties in the Garden

Sometimes, plants just die, leaving holes in the garden and in the hearts of those who tend them. What did we do? Where did we go wrong? The answer invariably turns out to have something to do with watering, and often we were doomed from the start.

The perfect example in my own garden was a favorite rockrose. I love rockroses. In the Mediterranean, they are the main constituent of the equivalent to our own chaparral, covering the dry, sunny slopes of Spain, southern France, Italy and Greece. They have a piney, summery scent and papery flowers in profusion. The one I like best is Cistus skanbergi , which has the most delicate of pink flowers, in the greatest number.

What is so maddening about this plant is how it lulls one into thinking that it has become a permanent part of the garden, only to suddenly depart. It’s a good deal like finally learning to live with a teen-ager only to watch him or her leave home.

This past summer, my favorite rockrose turned 5, after the best spring of its life. On March 20, it had been so covered with blossoms that I took a snapshot of it. I could have shot a whole roll--a photo a day--the show went on so long. In July, I became suspicious that all was not well when my wife called the office to tell me, “It’s blooming again.” Closer inspection revealed a few dead branches. A sentence in my garden log for Aug. 15 noted its demise. In September, I cut it back and dug it out. The hole it left was immense.

This is an all-too-familiar story in my garden. I am always trying to grow plants that are probably native to rocky crags or stony hillsides, but I garden on what was a flat lima bean field not so long ago. I’ve improved the soil and mounded up sections, but the garden is still not a hillside as hillside plants know it.

I suspect that the great majority of pretty plants grow on hillsides in their natural habitats. Plants native to California certainly do. The most valuable piece of gardening information any reference book could give would be a mention of how a particular plant grows in its native land, but books seldom explain anything about a plant’s environment. If one knew that a certain plant grew on hillsides, that would be a valuable hint--and a warning to flatlanders not to become too attached.

The reason these plants die on level ground is that they don’t get what garden literature refers to as good drainage. The soil stays wet too long after watering, and that encourages a group of organisms collectively called root rots. As I understand it, many fungus diseases are called root rots (the most notorious is oak root fungus), and all thrive when there is too much water in the soil. (That would be not much at all in the case of hillside plants accustomed to practically no moisture in the upper few inches of the soil.) These diseases are most active during the warm months of the year--which, unfortunately, coincides with when you water most in your garden. My casualty had a white mold covering its roots.

One solution is to avoid dealing with plants known to be susceptible to root rots (those that the garden books say need good drainage). You could limit your interest to plants that naturally grow on rich, level ground, as do most annual flowers and many perennials. These are much less finicky about water. But that would rule out so many plants.

It would not, however, rule out another of the casualties in my garden. In one bed last summer, I lost a rather late planting of petunias and lobelia. After several of the plants died, I dug them up and discovered that they had never rooted.

I attribute this to confusion. While I was busy being careful not to over-water the rockroses and other tricky plants in the backyard, I forgot to water the easy plants in the front. Not completely: The petunias and lobelia got watered along with everything else, but they needed water almost every day at first, and not getting it, they didn’t venture forth with new roots. So as summer wore on, they languished, then died. I made a mental note and backed it up with a stern sentence or two in the garden log about the importance of watering often while plants are young and becoming established. Fortunately, with fall well underway, watering new plants isn’t the chore it is in spring or summer. But I will be much more diligent, nonetheless.

All of this points to a great fact of California gardening. Though watering is what we do most often, it is what we least understand. There are no general rules; every plant has its own requirements, some that we will never be able to meet. While you’re staring glumly at a dead plant in the garden, it is well that you remember this. And don’t be too harsh with yourself. Summer’s casualties are an inevitable part of gardening in California, and with that said, we can forgive and forget--and we can even get out there and try again. I already have a little cutting, made a year ago from my favorite rockrose, ready to go into the ground.