Too much Water – “Bathtub effect”

Customer – We put down topsoil, dug the hole and filled it with topsoil and peat moss, plus a handful of plant food. It’s in a very sunny spot in my yard. I’ve been watering it heavily each day, but there were a day or 2 when it rained and I didn’t water so maybe those days it got less than when I water it.

Response – This is one of the most vivid depictions of the bathtub effect I have ever seen! I’m almost tempted to ask if we can use her photos in a blog post about why we say not to amend the soil when you plant. Though it seems like adding topsoil and peat moss to the hole is doing a good thing for the plant, it very often causes what’s known as “the bathtub effect.” Basically, all those fluffy new materials have very large spaces between their particles so can hold a lot of water. However, the natural soil surrounding the hole has quite small spaces between its particles. When you water, you end up applying quite a bit, because the new materials can hold so much of it. However, as gravity begins to take its toll and the water starts to drain out of the hole, it slows to a halt. The effect is like trying to fit a huge crowd through a tiny door – while it will eventually drain out, a lot of time will have to pass for it to do so. And while the water waits to drain out, it sits around the roots of the plant, suffocating them. Panicle hydrangeas are particularly sensitive to these conditions, so respond very dramatically, as you can see here. The plant has been severely set back but it can be saved. It needs to be dug up and placed in a shaded, well-ventilated spot for a brief period to let the roots dry a bit and get them some oxygen. They root ball should be covered with a piece of burlap or an old sheet or something. While you are waiting, go back to the hole and thoroughly incorporate all the material you added with your native soil, mixing until they are all indistinguishable from one another. Then it can be replanted. Water carefully – enough to settle the soil but not enough to get back to soggy conditions. I also would not recommend building such a dramatic ring around the plant, as that is exacerbating the amount of water being applied. Instead, I would recommend planting it even with the ground and then putting down mulch around the plant – that will retain the water and prevent it from running off when you water.