Drilling and Planting

By Lori Chips 

Growing alpine plants directly in holes that have been drilled into tufa is another step beyond just using the tufa as an attractive stone in a planting. As a gardener, once you have seen a large chunk with established plants adpressed to the surface or dripping down the side of the rock, it is hard not to have one's covetous nature kick in.         

Young tufa, meaning the stuff that has been recently dug, tends to be softer and easier to drill, but any piece can have hard spots or places that are dense and less porous. For drilling, it will help to have a good, fairly heavy-duty portable drill on hand. Before I got started last year, I took a trip to the hardware store to look at drill bits, another important factor in this equation.

I was standing by the display, mulling over the choices, when a salesman came over to me, and tried to size me up. He pulled down a relatively inexpensive bit and showed it to me, saying, "This will be fine for wood; good for most home uses."

"I'm not drilling wood," I said.

He looked surprised and asked, "What, then?"

"Stone." (Even though tufa is soft stone, it does tend to beat up the bit).

"Okay," he said as his hands moved over the display again. "This one should do it. Just putting in a couple of holes?"

"No," I said, looking him in the eye. "Hundreds."

He looked down and saw the heavy-duty, one-inch-wide masonry bit already in my hands then he nodded vaguely and walked away.

Since that first trip, I have realized that it's helpful to have a couple of bit sizes. Not all young plants, seedlings, or cuttings will require the same dimensions. For this project, it really is best to procure the smallest, youngest plant material, as it always seems to establish better.

When drilling your holes, there are a few things to keep in mind. First, try to determine which side will be up with your piece of tufa. Think of how it will be seated when displayed. This can play a part in selecting planting-hole sites. Obviously you do not want to plant one trailing beauty over another. Keep in mind how much (20%-30%) of the stone will be buried. You will not be drilling there. Before you start, have a discerning overall look at the piece. It often becomes obvious that too many holes in certain areas will compromise the strength of the shape, so don't create a perforation line along which the tufa will break.

As to the depth of the hole, the debate on this rages forward. Some people like to drill right through so that the plant would be effectively rooting in the trough medium. Others of the cognoscenti feel the hole should be no more than 1-1/2" deep, allowing the roots to do the penetrating. At this point in time I am not sure there is a correct answer. There are too many variables. Each plant species is different, and each aspect and microclimate is different. A tiny seedling planted in a shallower hole is going to require more babysitting, at least initially.

Think, too, about the angle of your holes before you drill. If they are perpendicular to the ground, they will better able to accept rainfall and irrigation than a horizontal hole will. Horizontal sites would be perfect for those rarities that resent wetness at the crown; even a spot with an overhang could be used. In these cases, be sure the tufa is receiving enough moisture and that it is wicking up to the plant in question.

Almost everyone agrees that too much organic matter (e.g., peat, soil, compost, etc.) in the drilled hole is a big mistake. Since part of the success with plants in tufa is in not needing to use pathogen-prone soil, I tend to agree with the rule: "No Organics" at all! You will need to save every speck of tufa dust you drill out or that breaks off. This is perfect backfill. It can be combined judiciously with parts of the following: greensand, Spanish River carbonatite, a little turface, and pumice. The first two contain micro minerals. (Greensand is readily available; we now offer for sale bags of pumice at the nursery).

The trick is to come pretty close to bare-rooting your little plants; shake, tease or wash the soil off, and then gently, using a pencil to guide the roots, dangle them down into the hole, tucking in strays as you go. Begin to backfill by pouring the mix using a small spoon of a folded index card. Once filled, you can tamp the plant in carefully using the eraser of the pencil. Water in, using a fine rose. You will probably need to top up the mix a little after watering. Keep everything out of the baking sun for a week or two. And that's it.

What plants to grow in tufa? You can grow many plants that do not survive away from the mountains where they come from! Many others stay "in character" better, or simply don't succumb to as many problems. Here are a few suggestions, but remember, there is so much more experimenting to be done.

Available at the Nursery 

We have handsome chunks of tufa for sale at the nursery, including a small number of drilled and planted pieces. They vary in size and in price. These tufa rocks were planted last August and the small alpines (many of which flowered this spring) have only to increase in size, beauty and venerability.