diff --git a/backend/src/utils/validation.js b/backend/src/utils/validation.js
index 372adb3..78cd973 100644
--- a/backend/src/utils/validation.js
+++ b/backend/src/utils/validation.js
@@ -87,7 +87,18 @@ const userProductSchema = Joi.object({
   productType: Joi.string().valid('granular', 'liquid', 'seed', 'powder').allow(null).optional(),
   activeIngredients: Joi.string().allow(null).optional(),
   description: Joi.string().allow(null).optional(),
-  isAdvancedEdit: Joi.boolean().optional()
+  isAdvancedEdit: Joi.boolean().optional(),
+  // Spreader settings for granular products
+  spreaderSettings: Joi.array().items(
+    Joi.object({
+      id: Joi.number().optional(), // For frontend temporary IDs
+      spreaderBrand: Joi.string().max(100).required(),
+      spreaderModel: Joi.string().max(100).allow(null, '').optional(),
+      settingValue: Joi.string().max(20).required(),
+      rateDescription: Joi.string().max(200).allow(null, '').optional(),
+      notes: Joi.string().allow(null, '').optional()
+    })
+  ).optional()
 });
 
 // Application validation schemas