River Birch Iron deficiciency
I have used plugs a twice over a 6 year period and they worked well. This year I decided to try Liquid Iron (Bonide Garden Rich). I have a large, 4 trunk birch about 25 years old. Qestion: Do I apply this at the base of the trunk or at the drip line? In this case the drip line will be about 15 ft or so from the trunk. Thank you!! The directions state to apply mixture around the perimeter of the trunk within the root zone. How far from the trunk is the root zone? Thanks again for your help. Meg
Kane County Illinois
Your river birch (Betula nigra) may be experiencing a couple of different problems. Depending on your soil, the surrounding soil may not be acidic enough to support the tree properly. Assuming you've done a soil test and know that adding iron will address the problem, then that's the way to go. The root drip line extends (approximately) as far out as the branches go. So if your tree is mature and the branches have spread quite wide/far, then you'll need to treat quite a bit of space.
This article from the University of Illinois explains iron chlorosis treatment:
Additional information is here: http://web.extension.illinois.edu/cfiv/homeowners/010616.html
If you haven't tested your soil to determine its pH or other properties, here is a list of soil testing labs: https://extension.illinois.edu/soiltest/