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What is Difference Between Aged Bark and Compost?

Can someone explain to me the main differences between garden waste compost and "aged bark"? Garden waste compost is made from the material collected by garbage companies in the green waste bin: yard cuttings, branches, and leaves. Aged bark is presumably a well-composted bark from conifers. A vendor for Clematis plants has a container soil that they insist should have a high proportion of "aged bark". When I explained that our local wholesalers sell well-aged garden waste compost - and aged bark is hard to find - they insist that compost is different than aged bark and has worse performance charateristics. Can someone clarify what those differences might be?

I assume aged bark is more acidic since conifer bark is acidic. But in terms of consistency, hydration, and soil performance characteristics, I would expect the two materials to be very similar. What are the important differences?

One thing I have noticed is that the garden waste compost I buy actually has a drying effect on soil mixes. Because it has small particles, it definitely does attract water on the surface of the many small particles. So right after watering there is a lot of moisture in the soil. But compost does not appear to absorb much of that water into its small particles. As a result, soil mixes made with the garden waste compost seem to dry out quickly. This is in contrast to peat moss, which seems to act like a sponge and absorb water deeply into the peat. If I have too much compost in a container soil mix, I end up being forced to add some peat to prevent the mix from drying rapidly. The need to balance these two ingredients can make things tricky, especially when I want to limit the total organic content of a container soil.

Yes, I understand the theory of perched water tables and the need to limit the total moisture that remains in a container soil. I measure these characteristics carefully. That said, some moisture-loving plants like Hydrangea really prefer a well-drained soil that retains a large amount of moisture.

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