Last week I ran the jar shake test on a scoop from my tiny rooftop bed since the store-bought pH strips kept giving random readings. Mixed it with water plus one drop of dish soap, shook it hard, and let it sit overnight. The settled layers showed a thick clay section at the bottom and almost no organic material floating on top. That lines up with why the tomatoes stayed stunted even though light and watering looked fine. For this kind of city soil, what cheap amendments have actually loosened the clay enough to help root growth?