Too Much Rain and Trees

So lets talk about the weather… Yup, too much rain. Who would have thought that in South Dakota in the summer we would be worrying about too much rain? But, here we are. So why is this a concern, and how will this affect our trees?

Root of the Issue

All this rain and how it will affect our trees all comes down to the soil and the tree roots. Most urban soils, and our soils in general, do not have enough organic matter in them. Couple that with poor soil structure, like too much clay, and the air spaces in the soil are small and limited.

Plant Roots need oxygen (air) to survive! They must have it. The excessive rain fills up most of those pore spaces within the soil and the tree roots die. When the roots die back, the trees cannot get water, so they get stressed. Interestingly enough, the symptoms expressed by the tree from too much water are the same as drought. Because its the same, the tree cannot get the water it needs to survive.

This high amount of rain we have been getting over the past year or so is just about as bad as a severe drought to some of our trees.


The second factor from all the rain that will affect our trees is it leaches (or washes) out the nitrogen in the soil. You have likely heard me say in the past we usually don’t need to fertilize our trees, but this year will be different. The high amount of rain has depleted the nitrogen in most of our urban soils. We don’t and won’t see much of that effect yet since the water can keep most things green. But, we will notice the effects of the lack of nitrogen in later years when (if) the weather dries up and the plants need the nitrogen to function and grow green growth.

The take home here is, if you want to stay ahead of the issue, plan to fertilize your trees this fall.


The last thing, but certainly not the least, is that the high amount of water going through our soils, raises our already high pH. That is why chlorosis is so rampant this year in so many of our plants.

The higher the soil pH above 7.0, the less and less most micro-nutrients (iron, manganese, etc.) are available to the plant. They get bonded to nitrogen, and then trees susceptible to chlorosis cannot get access to it. Rarely do our soils not have enough iron or other micro-nutrients, it is that they are just not accessible to the trees.

Normally, our soils in Sioux Falls are around 7.2 to 7.6 with varying ranges depending on the areas of town. But now, with all the rain, those ranges are increasing, thus changing what the trees are normally used to.

So what’s the fix?

Well, as far as the rain goes… certainly don’t water anything. It just has to stop raining.

For the other issues, here are a few things that can be done to help stressed out trees:

  • Fertilize with a quality slow release nitrogen with added ammonium sulfate in the fall. My custom blend Geo-Green Fertilizer is specifically made for our area with rates of 27-2-10-7S.
  • Incorporate as much organic matter into your soil as possible. Compost, sedge peat, and biochar are all things that can be top-dressed or tilled into areas that will help.
  • Mulch your trees. Proper mulching around trees will reduce competition from turf and help balance soil moisture, as well as slowly build organic matter.
  • Apply 7-10 lb. of ammonium sulfate to your landscape. Top dress to lawns and/or spread under tree root zones or mulch rings. This will help lower soil pH for a period of time to help the trees gain access to vital nutrients.


We already have a lot going on with our trees, from emerald ash borer to pine wilt and iron chlorosis, so more issues are not what we need. However, this crazy weather is going to make it harder on our plants, so expect things to continue to get worse for our marginal trees unless you take some action to help them out.

As always you can call or text for a consultation or to ask questions, or head to for more information.