Questionwe live in the mount vernon area of western washington and planted a new lawn in late march. It's coming in beautifully except for two large patches over the drainage field that are shorter and more yellow than the rest of the lawn. We did not use top soil because we live on farm land, but are wondering if this was a mistake, and if so how do we fix now?
AnswerI see two options:
either the soil level about the drainage area is too shallow and it causes the drainage pit to pull water from the soil. the grass will thus be draught stressed. the yellow color and short growth is consistent with this.
alterantively, this area stays very wet (saturated) which can also prevent grass from growing. yellowing would then be a sign of root death.
If it is fairly dry, I suspect your drainage ditch is effective (too effective). I would add more soil to ensure that you have at least 6-8" of soil covering this area. YOu can lift the turf (cut it with about 1" of soil on the roots in 1x1' squares, lift and put aside). fill topsoil and replace the sod pieces. keep the well watered for about 2 weeks until they re-root. If the grass strand here is very poor, you can also remove it with a wide bladed shovel and simply reseed.
Technically it could also be something in the soil being brought in from the drainage system, but I suspect it is due to lack of water (good news: your drainage ditch works as it is supposed to).
farm land soil is generally of good quality and it would be a waste to bring in new topsoil (which may not be of as good quality). However, you may need additional soil to add if your grass does not have deep enough soil over the drainage areas.
