Certified Professional Horticulturist (CPH) Practice Exam

Why do interior plants require less fertilizer than outdoor plants?

1. Indoor plants are less of a problem; therefore, demand for nutrients is lower

2. The nutrients of indoor plants are not leached away by heavy rains

3. Indoor temperatures typically fluctuate less than outdoor temperatures, subjecting the plant to less change

4. They grow slower and their demand for nutrients is lower

The correct answer is: They grow slower and their demand for nutrients is lower

Indoor plants generally require less fertilizer than outdoor plants primarily because they grow more slowly. This reduced growth rate translates to a lower demand for nutrients since the rate of nutrient uptake is closely related to the rate of growth. In a controlled indoor environment, factors such as limited light, confined root spaces, and lower biological activity can slow down the growth process, which results in fewer nutrients being needed compared to outdoor plants that are growing rapidly in optimal conditions. While other factors may affect nutrient availability and absorption, such as leaching due to rainfall or temperature fluctuations, the key reason for decreased fertilizer requirements indoors lies in the overall growth dynamics of the plants. Consequently, providing too much fertilizer to indoor plants can lead to nutrient imbalances or toxicity, making it essential to calibrate their feeding based on their growth rate and environmental conditions.