Which of the following can be used to monitor soil wetness or dryness?

The correct choice emphasizes various tools specifically designed to assess soil moisture levels, which is crucial for determining the watering needs of plants and ensuring their health. Soil probes, tensiometers, and electronic moisture sensors are all instruments that provide reliable measurements of soil wetness or dryness.

Soil probes allow for the extraction of soil samples to visually inspect moisture content, while tensiometers measure the tension or suction in the soil, giving a direct indication of moisture availability to plant roots. Electronic moisture sensors utilize electrical resistance or capacitance to indicate soil moisture levels, offering a precise and often instantaneous reading of moisture conditions.

The other options include tools that serve different functions. Soil rakes and trowels are primarily manual tools used for soil cultivation and manipulation rather than moisture measurement. Fertilizer probes are designed for assessing nutrient distribution in soil but do not provide information about moisture content. Thermometers measure temperature and do not relate to soil moisture levels. Thus, the tools in the correct answer are specifically tailored to monitor soil wetness and are essential for effective horticultural and agricultural practices.