How do plants in the summer prevent the permafrost from thawing?

Permafrost definition:

Just as a puddle of water freezes on a frigid winter night, water that is trapped in sediment, soil, and the cracks, crevices, and pores of rocks turns to ice when ground temperatures drop below 32°F (0°C). When the earth remains frozen for at least two consecutive years, it's called permafrost.

Plants in the Tundra (for example) have adapted to permafrost in a variety of ways; The plants grow close together, low to the ground and they remain small. Soils are often waterlogged because of the permafrost underneath, hardy plants like moss can cope with seasonal drought and water-logging.

Plants also have adapted to the Arctic tundra by developing the ability to grow under a layer of snow, to carry out photosynthesis in extremely cold temperatures, and for flowering plants, to produce flowers quickly once summer begins. A small leaf structure is another physical adaptation that helps plants survive.