Plants closer to the Earth are more likely to benefit from the heat released from the Earth’s core at night. However, as we know, this may not be enough to save them from frost. Instead, if your plants are low (and not potted or hard to move) you can create a warmth barrier using layers of straw or leaf mould about 10cm thick, to keep in their heat.
Keep in mind, that for taller plants, the roots will be affected differently than the foliage as there may be a considerable amount of distance, and consequently temperature, between them. Soil, and the nutrients it holds, can be affected by frost. Protect the ‘soil life’, and provide a layer of protection, by mulching bare soil with compost or manure.