Bottle Tree? Kurrajong? Which is it?

            I thought I would talk about “Bottle trees”. The reason for that? I get so many darned questions about them from readers. I get more questions from confused readers about this tree than any other landscape tree. These aren’t usually good questions; they are problem questions. All these problem questions makes you wonder if they should be planted in our warm desert at all! They should but choose a good planting location and water them carefully and not haphazardly.

The true Bottle Tree, Brachychiton ruprestis, has a bottle-shaped trunk. The Kurrajong, B. populenum, has a straigter trunk and is oftentimes called "Bottle tree" in the US. (Picture sent by reader in Australia where they are native)

What you are buying from the nursery (Brachychiton populneum) is not really a “Bottle tree” at all. The correct name is “Kurrajong”. The true bottle tree (B. ruprestis) is very different from the nursery version because its trunk is truly shaped like a bottle! It’s a beautiful oddity in the landscape. But the true Kurrajong hybridizes very easily with other types of so-called “Bottle trees”. The growers propagate “Bottle trees” from seed. Seed results from a cross between “mama” and “papa”. Unless the growers are knowledgeable, who knows what you are getting?

The Kurrajong, (B. populneum) which we here in the US oftentimes mistakenly call a Bottle tree, does not nearly have the trunk taper of  B, ruprestis. Picture sent by reader in US.

 The number one questions I get is about watering. They grow primarily in the dry interior of Australia. They are not a “swamp tree” and they are not a cactus but something in between. When you water them, think of them more like watering a palm tree (e.g., date palm) or even asparagus; they like to have their “toes” constantly in water but without the soil around them continuously wet or they will die.

Be very careful of overwatering Bottle trees, any of them. It is a delicate balancing act of giving them enough water vs watering too often when planted near or in a lawn.,

Leaf drop can be normal. It frequently will drop leaves just before  or if it’s not getting enough water (that does not mean water it more often!)

The horizontal branching and thin bark of the so-called Bottle tree can lead to sunburn if the canopy begins to thin due to leaf drop.

Plant in the spring, not during the hot summer months. Unlike palm trees, they don’t grow well after planting during the heat. Yes, they should be watered more often after first planting; maybe twice a week in the spring or fall rather than once a week. But after one growing season, apply a lot of water to a large area under its canopy but water less often. This means either apply the water slowly as in drip irrigation or build a mound or moat around the tree to hold the water so that it sinks in the ground. Applying a lot of water at once uses the same amount because “little sips are combined into one big gulp”.

Leaf scorch followed by leaf drop can occur because of watering too often or not enough water. Seldom is it from giving the tree too much water at one time unless the soil has poor drainage. Poor shade from the canopy can lead to sunburn of thin-barked limbs, particularly horizontal limbs.

The second problem I hear about from readers is sunburn or sun scorch on their primarily horizontal limbs. Sunburn on the limbs is for two reasons; the first is because this tree has very thin bark easily sunburned by intense sunlight and the second reason is due to where it’s planted. Never plant this tree in the hottest locations. It’s not a mesquite, Cordia or sweet Acacia.