Countermeasures to reduce the transfer of a radionuclide from soil to plants are usually based on saturating the soil with a stable element that is a chemical analogue of that radionuclide. But when a radioactive contamination event occurs, it is seldom due to the evacuation of a pure radionuclide such as 137Cs. Instead, a mixture of radionuclides may be released into the environment. The countermeasures applied to reduce the transfer of one of them may also influence other radionuclides. We have developed an experimental procedure to check whether radiocaesium countermeasures are appropriate when other radionuclides are also involved, or have some disadvantages that may limit their use. It consists of growing wheat seeds under controlled laboratory conditions using Neubauer's plantlet method. This method has been in use for many years as a small-scale screening procedure to check a soil's capacity to provide the potassium that plants need as a nutrient. In particular, we used it to study the effectiveness and the disadvantages of the application of a potassium salt fertilizer to a soil contaminated with 134Cs, 90Sr, and 60Co. This countermeasure indeed reduced the uptake of 134Cs, but it also enhanced the uptake of 60Co. This enhancement was higher for the wheat stems than for the roots. For 90Sr, there was observed a slight increase due to the fertilizer.