Question: Is it true that certain types of tree leaves are highly acidic? Should I think before shredding them and using them as mulch?
Answer: You're probably referencing the old myth that oak leaves shouldn't be used as mulch. Experts with University of Missouri Extension note that oak leaves are acidic, but pH is not a big concern with mulches, because mulch is put on top of the soil, not worked into it. Oregon State Extension concurs and adds that many organic mulches (besides oak leaves) are acidic, yet only very sandy soils are susceptible to pH changes due to mulch. Other soil types "buffer" potential changes. If the mulch is applied repeatedly, the top two inches of soil may become slightly more acidic, but this will not affect most plants. The best way to know and monitor your soil's pH is to test it; you can also gauge soil pH by growing certain pH-indicating annuals.
Get an illustrated guide to 5 fall garden tasks for under $5
Find resources for a green lifestyle
Browse outstanding gardening tools, including heavy-duty work gloves.