Which of the following is a disadvantage of using media in greenhouses?

Using media in greenhouses can present several disadvantages, one of which is the lower cation exchange capacity (CEC). CEC is a critical property of growing media as it indicates the ability of the medium to hold and exchange cations—positively charged ions that are essential nutrients for plant growth, such as calcium, magnesium, and potassium.

When a growing medium has a low CEC, it means it has a reduced ability to retain these nutrients, leading to potential nutrient deficiencies in plants. This can necessitate more frequent fertilization to ensure that plants receive adequate nutrition, which can increase labor and material costs.

In contrast, high water holding capacity is typically an advantage, as it helps maintain moisture levels for plant roots, and natural nutrient availability indicates that the medium can supply nutrients inherently, which is beneficial for plant health. High density in media is not intrinsically a disadvantage as it can help with stability and support for plant structures. Thus, the significant drawback of lower cation exchange capacity demonstrates why this characteristic is a notable concern when managing greenhouse media.