Hi @rmrama,
Welcome to the Bunnings Workshop community, it's wonderful to have you with us. Also, many thanks for your question about your dwarf meyer lemon tree.
As you're aware, yellowing leaves can be related to nutrient imbalances, and by the sounds of your product applications, it is more likely an overabundance or inability to uptake those nutrients than a lack of nutrients. I'd suggest reducing the number of products you are using by switching over to a slow-release, citrus-focused fertiliser such as this Scotts Osmocote Citrus and Fruit Controlled Release Fertiliser. For the time being, I would halt your product applications and wait a month or so before applying the slow-release fertiliser following the manufacturer's application instructions closely. This will simplify the process and ensure your tree is getting the right amount of nutrients.
Soil PH may also be a factor. If the PH of the soil is off, this can affect your tree's ability to intake those nutrients. Lemon trees like slightly acidic soil, between 5.5 and 6.5. Grab a Manutec Garden Care Products Soil PH Test Kit, test the soil and make adjustments accordingly. If the PH needs to be increased, add Richgro Natural Garden Lime, if it needs to be reduced add Yates Sulfur Soil Improver Granules.
Another potential reason for the yellowing is the clay soil. Clay soil tends to retain moisture, which can lead to waterlogging. While you've added good organic matter, the tree could still be struggling with drainage if the surrounding clay holds too much water. Improving drainage can be done by aerating the soil around the tree with a garden fork and adding Yates Gypsum Clay Breaker Soil Improver Granules.
You should also always check the top 3-5cm of soil before watering. If the soil is damp, wait a few days before testing again. If the soil is dry, then water away.
You might also like to check out How To Grow And Care For a Lemon Tree for some additional guidance.
Let me know if you have any further questions.
Jacob
