Love the look of the Catalpa Bignoniodes aka ‘The Indian Bean Tree’ but lack the space to put it?
Meet its smaller sibling…
The Catalpa Bignonioides Nana
This is the dwarf variety of the Indian Bean Tree. (Nana’s the botanical Latin word for dwarf)
By dwarf, what’s meant is that it’s small when planted, but given time, it still grows to a decent size.
The Growth and Spread of the Catalpa Bignonioides Nana
4 meters tall with a 3-metre spread is what some nurseries claim.
… With it taking up to 25 years to reach that size.
The RHS has a more realistic expectation for size.
1.5–2.5 metres in height and spread, and taking 5 to 10 years to reach that.
That’s what you call a slow grower!
To keep its size in check and maintain its dwarf size, it needs to be pruned, and trained. (more on that to come).
Size Matters!
Know this before you go to the nursery or search online for one of these…
The Catalpa Bignonioides Nana cultivar is top-grafted.
Therefore, pay attention to the height you’re buying.
This is the reason these are called dwarf species.
The height of the tree is the height of where the graft is.
That’s the part where the rootstock (base) connects to the scions (branches).
The girth of the trunk will get chunkier, but it won’t grow taller.
For that reason, when buying a Catalpa Bignonioides Nana, know and understand the options.
The height that’s described is usually referring to the clear stem. That’s the height of the rootstock, before the graft union.
- A quarter-sized tree is one with a clear stem under 4ft.
- A half standard is (4 ft – 5 ft).
- A standard tree is 6 ft.
Given that the Catalpa Bignonioides Nana is a dwarf species, it’ll be a quarter size. A “Standard Catalpa Bignonioides” is probably not the “Nana” cultivar.
An earlier post discussed how to grow and propagate an Indian Bean tree, but do note that only a true Catalpa Bignonioides blooms.
Dwarf varieties are less likely to flower, and are grown for the foliage only.
Given that these are slow growers, a wise choice would be to buy from a reputable supplier with experience grafting trees.
You can buy Catalpa Bignonioides Nana cultivars in heights from around 100cm, up to 300 cm.
Trees with a clear stem up to 25 cm will be in containers up to 25 litres.
Trees with a larger rootball may be wrapped with wire.
How to Plant the Catalpa Bignonioides Nana
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Root inspection and loosening
Trees are not supposed to be grown in containers. When they are, the roots encircle the pot.
When you put it in the ground, you want those roots to anchor so they can grab as much nutrients from the soil as possible.
To achieve that, give it a helping hand by removing the tree from the container, (or the wire it’s wrapped in) and loosen the roots so you’re not planting a compacted rootball.
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Get the depth of the hole right
If your tree came in a container, that’s what to use to measure the depth of the hole you’re planting the tree in.
Otherwise, measure the height and diameter of the root ball and dig a hole large enough for it.
Add 2 cm of depth so that the top of the rootball is 2 cm below the soil line.
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Plant your tree and backfill with soil
With your tree in the ground, backfill with the soil you dug out.
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Topdress with a quality compost (optional)
Topdressing with a nutrient-rich compost can benefit newly planted trees, especially if the compost used is enriched with a slow-release fertiliser.
As rainfall (or watering) moistens the compost, trace minerals enrich the soil beneath, providing the roots with nutrients required for strong root growth.
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Water it well
Once you have the tree bedded in, deep water it at the soil level.
That’s to say, water it until it starts pooling. Don’t leave a puddle of water on the soil.
Established trees will find water, but young trees need help.
Catalpa Bignonioides Nana Problems to Watch For
Much of the Indian Bean Tree problems and diseases apply to the “Nana” cultivar too.
And because it’s smaller, the symptoms are more pronounced.
It’s also not as hardy, and that brings unique challenges.
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Windburn or leaf scorch
Windy days are great drying days – when it’s laundry. Not for drying out the leaves on your trees and garden plants.
The Catalpa Bignonioides Nana is not an evergreen. It’s a deciduous tree that sheds its leaves in the winter. When new leaves emerge, cold winds can scorch them.
The result will be brown leaves that are crisp around the edges.
It’s for this reason that it ought to be planted in a sheltered location.
It does prefer full sun, but if that exposes it to harsh winds, opt for partial shade in a sheltered location instead.
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Graft Failure
This is an inherent risk to all dwarf cultivars. Not just the Catalpa Bignonioides Nana tree.
If the graft fails, the tree dies!
And that is a good reason to plant this in a sheltered location, away from potential high winds.
A mechanical failure of the graft union cuts off the nutrient supply from the rootstock to the scions. No nourishment from the ground soil will make its way to the branches up top.
The result will be a loss of vigour, and depending on the extent of the damage, that could be fatal fast.
Other than those two problems that are specific to the Nana cultivar, the only other problem is keeping their size in check with pruning.
And, you ought to prune this annually, not just to benefit from large leaves and a manicured globe shape, but to keep the size in check so as not to overly stress the graft area.
Too much weight up top could see the partial separation of the graft union – where the rootstock attaches to the scions.
How and When to Prune Catalpa Bignonioides Nana
Prune Catalpa Bignonioides Nana once a year. Early spring is ideal.
The leaves turn a golden yellow in the autumn, before dropping over the winter. New leaves appear from Spring the following season.
In early spring, cut away damaged branches, and prune for shape to maintain a spherical crown.
Once the tree matures, you may want to cut back some of the lower branches. Those will be the oldest.
Removing old branches with smaller-sized leaves helps channel energy toward producing new healthier and larger leaves up top.
