Planting a Western Pecan Tree (Carya illinoi) in Southern California

Question from Frank:
I’m interested in planting a Western Pecan tree in my yard and am looking for tips on soil preparation, watering, pruning… to help ensure it not only survizes but eventually fruits for me. I live on the south face of the San Gabriel Mtns north of Los Angeles (Sunset climate zone 21), my soil is a mix of very fine dirt (that water just sits on) and rock. Any hints?

Answer from Pat:
When planting any tree we should always begin by thinking about it’s characteristics and requirements. Pecan trees (Carya illinoiensis) are native to the south central areas of USA. They need long hot summers and regular irrigation. Also they are mature deciduous trees, growing as tall as 70 feet when full grown. They are shapely and will even grow in lawns if watered and fed sufficiently so they can out-compete the grass. Your climate Zone 21 usually does not provide the optimum summer heat and cold for good crops, but nonetheless I once knew of a pecan tree growing in Sunset Zone 21 and it did very well and provided adequate supplies of nuts for the homeowner, heavier always on alternate years, which is natural to pecans. Also, pecan trees really should have a pollenizer. There are two types of pecan (type 1 and type 2.) You should provide one of each or at least be sure there is another tree of the correct type within a block or two of where you live for adequate pollination. There are also several varieties of each type of pecan so you will need to research to decide which variety you want, but in my opinion you should get the one called ‘Pawnee’ (type 1) since it does better where summers are cooler than a place like, for example, Visalia in the Central Valley, where pecan trees are about as happy with the climate as they can get. The pecan tree I knew in Zone 21 was a ‘Pawnee’ and the homeowner did not have a pollenizer but probably there was another tree in the neighborhood.

Now we come to the trickier part: your soil or lack of it. Pecan trees need deep, well-drained, fertile soil. This means as deep as 6 to 10 feet and with good drainage. They have a tap root that goes down deeply and anchors their mature height by deep rooting. Planted in shallow soil, a pecan will topple over and may die from root rot prior to that. You live in the San Gabriel Valley where if you lived just a little further away from the mountains you would be fine since the soil there is decomposed granite. The decomposed granite in the alluvial fans of the San Gabriel Valley is very fertile and deep. It drains beautifully and is minerally rich, but in some areas on the edges of these fans there is nothing but round rocks. Wild trees such as sycamores can even gain a foothold here and flourish. But when you are on proper decomposed granite all you need add is soil amendment and nitrogen. But where you live it sounds as if you are closer to the mountain side, maybe even up onto it where you have a view. If so, you are on bedrock, and this is most likely solid granite. With boulders of granite, you get drainage between them, but solid granite does not drain. It is a waterproof barrier. If I am describing the truth about your garden, (or “rock pile”), about all you could do is blast out the rock to a depth of at least 10 feet, making the bottom of the hole slope slightly away from the hill, put in drainage pipes (being careful to follow local laws on runoff), and gravel for drainage on the bottom and then refill the entire area with truckloads of well-amended top soil. To do this for one or two pecan trees does not sound like a good use of funds, unless for you funding is unlimited.

That said, I actually know of several cases where a new homeowner was an avid gardener and purchase a home with poor soil. In one case he bulldozed out about three feet of subsoil and replaced with top soil, in that case he also mounded it to make an interesting contour. Now forty years later that garden still thrives. But rock that does not drain is a different matter. If it were compacted clay it would be different. One could loosen it and add gypsum to increase drainage. I know of more than one case of gardeners blasting holes in rocks and planting trees but they were not pecan trees. The most famous case is Queen Hatshepsut, the remarkable female pharaoh of ancient Egypt who lived roughly three thousand, five hundred years ago. She was a plant lover, a plant collector, and plant explorer (or at least she hired folks to do this for her.) We could call her our first known historical horticulturist. In one spot where she wanted to make a garden she commanded that holes be dug in sheer rock and that they be filled with top soil. Into the holes she had her slaves plant palm trees. But we do not know how many years they lasted or if they had to be frequently replaced due to lack of drainage. It was like growing plants in pots with no holes in the bottom. As we know, this is a no-no and results in death of plants due to the build-up of salts and also root rot.

For more on the subject of dealing with poor soil or lack of soil altogether, please see the parts of my organic book that deal with all this subject (Pages 18 to 30.) Also for more about pecan trees such as how to deal with zinc insufficiency and other details, read pages 523 and 524 in the latest copy of Sunset Western Garden Book.