My location is Carlsbad, CA. 92011
1) What zone is it?
2) Also is this a good time to plant this tree? August
Answer from Pat:
Gold medallion tree (Cassia leptophylla) is one of our best small to mid-size flowering trees, good in patios or as a street tree. It is almost evergreen along the coast and semi-evergreen inland and flowers for a long season, mostly in summer. Though this tree has the reputation of growing rapidly to 20 or 25 feet tall and 30 feet wide, it can easily be kept to a compact umbrella shape by pruning. It is easiest to begin with a boxed specimen that is fairly large and already trained into a well-balanced umbrella shape on a single sturdy trunk. If you purchase a tree in a 5-gallon can you will need to prune and train the tree carefully in youth to encourage a sufficiently tall trunk, strong branch structure and even shape without lop-sided growth.
If you purchase a boxed tree, for the first year of two while the tree is getting established, prune it after bloom only enough to remove seed pods and dead wood and maintain a good even shape. Once it is the size and shape you want, cut it back annually after bloom. The right time to do this is in early fall (mid-September.) Remove all dead wood, if there is any, and cut back the branches on the sides and top of the tree to maintain a nicely rounded umbrella shape. By cutting back all over the top annually in early fall (after, not before, bloom) you can keep a cassia tree exactly the size and shape you want for many years. Make sure that the trunk is staked in such a way that it can move with the wind. This will make it grow strong.
Regarding your climate zone, if you look at the map on page 54 of the most-recent edition of Sunset Western Garden Book or follow this link: http://www.sunset.com/garden/climate-zones/sunset-climate-zone-san-diego-area-00418000067314/ , you will note that Zone 24 extends several miles inland in Carlsbad. In northern Carlsbad, Zone 24 extends approximately half way from the coast to Vista and in southern Carlsbad slightly further inland than Palomar Airport. This unusually wide band of Zone 24 is caused by the fact that the land slopes gently upwards for several miles from the ocean and this causes the warming influence in winter and cooling influence in summer of coastal winds, air, and fog to slide inland as far as the hill slopes upwards. These coastal conditions of Zone 24 don’t change to the slightly more extreme conditions (cooler in winter, warmer in summer and sunnier year-round) of Zone 23 until you reach the other side of the first hill away from the ocean. Additionally, in any climate zone you will always find some anomalies, called “micro-climates”. These are caused by sudden changes in topography, such as small valleys, canyons, dips, mesas, or even man-made structures like walls or buildings. Some of the larger and more easily recognized micro-climates created by the natural lay of the land in Carlsbad include south-facing properties just north of Batiquitos, Agua Hedionda, and Buena Vista Lagoons that are protected from ocean wind. These areas enjoy salubrious micro-climates a few degrees warmer year-round than most of Zone 24 and thus they are conducive to growing many subtropical and tropical plants, including orchids, bananas, mangos and other tropical fruits.
To answer the third part of your question, yes August is a fine time for you to plant this tree, especially considering your warm mild climate. Cassia is a subtropical tree and therefore its roots will become better established in warm weather. Be sure to provide good drainage. (See page 40 of my organic book for detailed directions on this topic.) Keep well and deeply watered after planting. In the town where I live two large boxed cassia trees in excellent condition and flowering massively were recently planted into holes cut in sidewalk. Despite my repeated cautions, the owners of the property failed to water deeply enough to soak the entire root ball and both trees wilted. Lay the hose on the ground within the watering basin under the tree and allow the water to run slowly for several hours so that it really penetrates the ground. Sprinklers are not enough. Here is an additional tip: If you will apply humic acid or John and Bob’s Soil Optimizer according to package directions to the ground, this can help the roots of newly planted trees to get established quickly.
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