In accordance with Article 6 of Regulation (EC) No 396/2005, the applicant BASF Agro B.V. Arnhem (NL) Freienbach Branch submitted a request to the competent national authority in the Netherlands to modify the existing maximum residue levels (MRLs) for the active substance potassium phosphonates in leeks and spring onions/green onions/Welsh onions. The data submitted in support of the request were found to be sufficient to derive MRL proposals for the commodities under assessment. Adequate analytical methods for enforcement are available to control the residues of potassium phosphonates in accordance with the proposed residue definition ‘phosphonic acid and its salts expressed as phosphonic acid’ on the commodities under consideration. Based on the risk assessment results and assuming that the exiting MRLs will be amended as proposed by EFSA in previous outputs, EFSA concluded that the long‐term intake of residues resulting from the use of potassium phosphonates according to the reported agricultural practices is unlikely to present a risk to consumer health. Considering the toxicological profile of the active substance, a short‐term dietary risk assessment was not required. The risk assessment shall be regarded as indicative because some MRL proposals derived by EFSA in the framework of the MRL review according to Articles 12 and 43 of Regulation (EC) No 396/2005 require further consideration by risk managers.