As I suspected, someone has been adding soil to my garden. The plot thickens.
Why this joke works
Soil Makes the Plot Thicken
“The plot thickens” is a storytelling expression meaning that events have become more complicated or mysterious. A garden plot is also a defined piece of ground used for growing plants. Adding soil can literally make that plot thicker. The opening “as I suspected” imitates detective fiction, strengthening the narrative meaning before the gardening detail takes over. Both senses of “plot” and “thickens” remain active in the same sentence.
A closer look
A Mystery Plot Gains Literal Garden Material
“As I suspected” gives the line the voice of a detective announcing a discovery. Soil accumulating in a garden sounds ordinary, yet describing an unknown culprit makes it evidence. “The plot thickens” then joins story complication with a garden plot physically gaining material. The formal first clause and familiar dramatic closing make a tiny landscaping change feel like the next chapter of a case.
Fact behind the joke
Organic Matter Can Change Soil Structure
USDA Natural Resources Conservation Service guidance says organic matter helps bind soil particles, improves aggregation, increases water infiltration, and supports biological activity. It can also hold far more water and nutrients than the same mass of soil minerals. Adding arbitrary soil is not automatically good gardening, but carefully managed compost, plant residue, cover crops, and reduced disturbance can improve a garden’s physical structure over time.