Symptom reading1 released

Symptom reading

A field symptom read back to the parameter that caused it, not to a product.

Symptom reading table

Four field symptoms, each read back to the parameter that produced it rather than to a product. The last column is the one number that row turns on, with the threshold drawn on it.

Reading	What you see	Chain of causes	Parameter correction	Field confirmation	Scale
Bare patches2026-09-29	This row is released with the 2026-09-29 entry, and will carry the same four columns as the others.				4 wk weeks to close
Moss2026-10-17	This row is released with the 2026-10-17 entry, and will carry the same four columns as the others.				pH 5.5 soil pH
Thatch over 15 mmreleasedflag the species on the bench →	Thatch layer 15 mm or thicker recovery window 4–12 wk	Nitrogen has been applied above the species budget for several seasons, producing more lignin-rich stem and stolon tissue than the soil can decompose. Clippings have been bagged for years on a lawn that is now below 10 mm of thatch, removing the nitrogen the microbes need to break the mat down. Soil pH has drifted below 5.5, collapsing the bacterial population and shifting decomposition to slower fungal pathways. The lawn is a species with a thatch tendency of 5 out of 5 and has never been scarified. Irrigation is frequent and shallow, keeping the surface constantly moist and the mat compressed rather than allowing it to dry and fracture.	Scarify 5 mm, in early autumn when soil temperature at 50 mm is between 15 and 21 degrees Celsius, with the tines set to just graze the mat. Overseed the same day at the full species rate, 10 to 15 g per square metre for Kentucky bluegrass, 25 to 35 for perennial ryegrass, 30 to 40 for tall fescue. Topdress 1 to 2 mm of sand-loam matched to the root zone, then water 6 to 10 mm a day for ten days. Cut the annual nitrogen to the species budget: 15 g per square metre for Kentucky bluegrass, 10 for zoysia, 6 for centipedegrass and fine fescues. Raise soil pH into the species band with 200 to 250 g per square metre of lime on a loam, applied in the following autumn and retested after 12 months. Switch to mowing at the top of the species band and mulch the clippings, which returns 1 to 2 g of nitrogen per square metre per year.	Cut a 100 mm square flap of turf with a knife, lift it like a hinge and read the brown fibrous layer between the green leaf bases and the dark soil with a ruler. Do it in three places. Push a screwdriver into the profile; if it stops in the mat before reaching soil, the layer is thick and hydrophobic. Watch a hose test: water beading and running off a dry lawn instead of soaking in is the signature of a hydrophobic thatch layer. Check for the crown being lifted above the soil line by parting the grass with both hands; crowns 15 to 20 mm above soil dry out in two days.	15 mm mat depth
Broadleaf weeds2026-11-01	This row is released with the 2026-11-01 entry, and will carry the same four columns as the others.				15 g annual N

2026-09-15

Thatch over 15 mm: reading the mat and correcting the parameters that built it

A thatch layer above 15 mm is a structural problem, not a cosmetic one. It sheds water, lifts the crowns above the soil where they dry out, and harbours the fungi that cause patch diseases. The…

4–12 wk