We planted three lemon myrtle (Backhousia citriodora) in November last year. They have been struggling lately and I can't work out what is going wrong with them. I have recently treated them with two doses of Mancozeb Plus and now they are just dropping leaves and looking very unhappy.
I have attached some photos - the first is when they were first planted and looking happy and robust. the remainder were taken this morning with the most unhappy tree and some close ups of the leaves.
They are in a large planter box and get sun through the day and shade late in the afternoon. Each plant is contained in a Greenwell Green Water Saving Plant Surrounds to help with concentrating the water. We are in Sydney.
Welcome to the Bunnings Workshop community @erin1. It’s great to have you with us and many thanks for your question on plant care.
From the photos, I suspect the trees are suffering from environmental stress rather than a fungal disease. The sparse foliage, leaf drop and darkening of the leaves could be consistent with root stress, particularly from the soil remaining too wet.
The surrounds are useful for directing water to the root zone, but in a raised planter like this I’d be cautious about concentrating too much water around the trees. Lemon myrtles appreciate consistent moisture but still need good drainage and oxygen around their roots. With Sydney's cooler winter conditions, the soil will also remain damp much longer than it did when the trees were planted in November.
Before applying any more Mancozeb, I'd stop treatment for the moment and check the soil moisture. Dig down around 100mm beside each tree and see whether the soil is still damp. If it is, allow it to dry somewhat before watering again. I'd also check that water can freely drain from the planter and isn't being trapped at the bottom.
The trees still appear to have plenty of living stems and some new growth, so I certainly wouldn't give up on them. You can lightly scratch the bark on some of the apparently bare branches. If it's green underneath, they're still alive and should be left in place. Any branches that are brown and dry all the way through can be pruned back to healthy growth.
I'd concentrate on getting the watering and drainage right and give them a few weeks to respond as the weather warms. Once you start seeing healthy new growth, a gentle application of a suitable native fertiliser or seaweed tonic could help them recover. Here's a helpful guide: How to grow lemon myrtle. Let me tag @mich1972 and @Noelle to see if they have any thoughts.
Please let me know if you have any questions.
Mitchell
Thanks so much Mitchell!
The planter is actually just the sleepers built around a previous garden bed to give us height to try and provide privacy from our neighbours (the top of our fence (before we put the toppers on) was waist height for them and they are nosy). As such the raised bed doesn’t have a base.
I’ve just dug around the base of the middle tree and stuck a moisture meter in which says it’s dry+ at the top and Dry at full depth (about 20cm down). Apparently the ph is 7.0.
just as an add on Mitchell - I’ve just scraped back a few of the sad looking branches and they are green - :) so that is a relief!
That's great news @erin1. If you're seeing green beneath the bark, there's certainly plenty of life left in them.
Given the planter is open to the ground and your moisture readings are showing dry soil, I'd actually revise my thoughts on watering. It sounds more likely that they're simply not receiving enough water rather than remaining too wet.
I'd give each tree a good, slow, deep watering, extending beyond the Greenwell surrounds, and then check the soil again a day or two later. Ideally, you want the soil consistently moist but not saturated. A layer of organic mulch across the bed would also help retain moisture as the weather warms, keeping it clear of the trunks.
A pH of 7.0 shouldn't be particularly concerning.
Since the branches are alive, there's a good chance you'll see them start pushing fresh growth as conditions warm up.
Hi @erin1
From your most recent comments and the browning of the leaf margins, it looks like your trees are suffering from too little moisture, rather than too much. Planting trees into a raised bed like yours means water or rainfall will soak right through the bed into the soil beneath. This is fine once the trees are well established and have sent roots down deep into the soil but in the early years it could mean the soil in the raised bed is draining too well and drying out quickly around the roots. Medium to large trees and raised beds as you have are not a great combination. Eventually the bed will restrict root spread which may affect overall tree health.
Generally raised beds are better for perennials, low growing shrubs and vegetables - plants that don't have extensive or deep root systems
Hi @erin1,
I just thought I might add a link to our article on https://www.bunnings.com.au/diy-advice/garden/planting-and-growing/how-to-grow-lemon-myrtle as it has some good information and tips that you might benefit from reading.
Jacob
Just checking in to see how your lemon myrtle trees are going? Have they picked back up with the warmer weather and a bit of TLC?
It would be great to see an update if you have one. Hopefully they are doing well.
Hi Jacob!
Thanks to the super helpful feedback from this community we have seen them rally on! The smaller of the three is a bit slower but it is coming back to. Here are some photos:
That's fantastic @erin1. I'm so glad to see how just how much better they are looking. I expect things will kick on even more as spring progresses.
Thank you for the update.
