diff --git a/prisma/migrations/20260707012217_v0_28_root_vegetable_category/migration.sql b/prisma/migrations/20260707012217_v0_28_root_vegetable_category/migration.sql
new file mode 100644
index 0000000..ead75fd
--- /dev/null
+++ b/prisma/migrations/20260707012217_v0_28_root_vegetable_category/migration.sql
@@ -0,0 +1,2 @@
+-- AlterEnum
+ALTER TYPE "PlantCategory" ADD VALUE 'ROOT_VEGETABLE';
diff --git a/prisma/schema.prisma b/prisma/schema.prisma
index 4a992b0..dd889f9 100644
--- a/prisma/schema.prisma
+++ b/prisma/schema.prisma
@@ -122,6 +122,7 @@ enum PlantCategory {
   GROUNDCOVER    // strawberries, clover, creeping thyme
   VINE           // grapes, hops, kiwi
   ANNUAL_VEGETABLE  // tomatoes, squash, beans, peppers — seasonal veg
+  ROOT_VEGETABLE    // carrots, beets, sweet potatoes, radishes
   ANNUAL            // legacy, treated as annual vegetable
   ANNUAL_FLOWER     // zinnias, marigolds, nasturtiums, cosmos
   PERENNIAL         // asparagus, rhubarb, perennial veg
diff --git a/src/app/api/plant-types/route.ts b/src/app/api/plant-types/route.ts
index 5ce03a2..aca4866 100644
--- a/src/app/api/plant-types/route.ts
+++ b/src/app/api/plant-types/route.ts
@@ -17,7 +17,7 @@ const createSchema = z.object({
   bloomEnd: month.optional(),
   harvestStart: month.optional(),
   harvestEnd: month.optional(),
-  toxicToPets: z.boolean().optional(),
+  toxicToPets: z.boolean().nullable().optional(), // "Unknown" in the dialog arrives as null
   edibleParts: z.string().optional(),
   spacing: z.string().optional(),
   imageUrl: z.string().optional(),
diff --git a/src/lib/changelog.ts b/src/lib/changelog.ts
index 04e68b6..d85c972 100644
--- a/src/lib/changelog.ts
+++ b/src/lib/changelog.ts
@@ -8,6 +8,15 @@ export type ChangelogEntry = {
 };
 
 export const CHANGELOG: ChangelogEntry[] = [
+  {
+    version: "0.28.0",
+    date: "2026-07-06",
+    changes: [
+      "Fixed: adding a new plant type by hand failed with a confusing \"expected boolean\" error when \"Toxic to pets?\" was left as Unknown. Leaving it Unknown works now.",
+      "New \"Root vegetable\" category for plants and plant types — carrots, beets, sweet potatoes, radishes.",
+      "The garden brain now knows sweet potatoes (including Japanese ones): plant slips in warm June soil, dig before the first fall frost, cure warm to sweeten.",
+    ],
+  },
   {
     version: "0.27.0",
     date: "2026-07-06",
diff --git a/src/lib/garden/categories.ts b/src/lib/garden/categories.ts
index d70fc8c..26b17be 100644
--- a/src/lib/garden/categories.ts
+++ b/src/lib/garden/categories.ts
@@ -9,6 +9,7 @@ export const CATEGORY_LABELS: Record<PlantCategory, string> = {
   GROUNDCOVER:      "Groundcover",
   VINE:             "Vine",
   ANNUAL_VEGETABLE: "Annual vegetable",
+  ROOT_VEGETABLE:   "Root vegetable",
   ANNUAL:           "Annual vegetable",
   ANNUAL_FLOWER:    "Annual flower",
   PERENNIAL:        "Perennial",
@@ -29,6 +30,7 @@ export const CATEGORY_ORDER: PlantCategory[] = [
   "PERENNIAL",
   "PERENNIAL_FLOWER",
   "ANNUAL_VEGETABLE",
+  "ROOT_VEGETABLE",
   "ANNUAL_FLOWER",
   "BULB",
   "MUSHROOM",
diff --git a/src/lib/garden/knowledge.test.ts b/src/lib/garden/knowledge.test.ts
index 7a145a8..ce09056 100644
--- a/src/lib/garden/knowledge.test.ts
+++ b/src/lib/garden/knowledge.test.ts
@@ -22,6 +22,12 @@ describe("knowledgeFor", () => {
   it("returns null for unknown plants", () => {
     expect(knowledgeFor("Dusty Miller")).toBeNull();
   });
+
+  it("prefers the most specific match — sweet potatoes are not potatoes", () => {
+    expect(knowledgeFor("Sweet potato")?.name).toBe("Sweet potato");
+    expect(knowledgeFor("Japanese Sweet Potato")?.name).toBe("Sweet potato");
+    expect(knowledgeFor("Potato")?.name).toBe("Potato");
+  });
 });
 
 describe("tipsForMonth", () => {
@@ -37,6 +43,13 @@ describe("tipsForMonth", () => {
     expect(nov.some((t) => t.crop === null && t.action.includes("Winter-mulch"))).toBe(true);
   });
 
+  it("suggests only the best-match crop — no potato-hilling for sweet potatoes", () => {
+    const june = tipsForMonth(6, ["Japanese sweet potato"]);
+    const actions = june.map((t) => t.action);
+    expect(actions).toContain("Plant sweet potato slips");
+    expect(actions).not.toContain("Hill potatoes");
+  });
+
   it("dedupes when several plants match the same crop", () => {
     const july = tipsForMonth(7, ["Bearded Iris", "Iris sibirica", "Yellow Flag Iris"]);
     expect(july.filter((t) => t.crop === "Iris")).toHaveLength(1);
diff --git a/src/lib/garden/knowledge.ts b/src/lib/garden/knowledge.ts
index 3e6f70e..13bb3f4 100644
--- a/src/lib/garden/knowledge.ts
+++ b/src/lib/garden/knowledge.ts
@@ -140,6 +140,17 @@ export const KNOWLEDGE: CropKnowledge[] = [
       { months: [10], action: "Finish digging carrots", detail: "A light frost sweetens them; dig before the ground locks up." },
     ],
   },
+  {
+    name: "Sweet potato",
+    aliases: ["Japanese sweet potato"],
+    family: "root",
+    rotationNote: "Not a nightshade despite the name (it's a morning glory) — rotates fine after tomatoes.",
+    uwQuery: "growing sweet potatoes",
+    tips: [
+      { months: [6], action: "Plant sweet potato slips", detail: "They demand warm soil — early June here, black plastic mulch helps a zone-4 season." },
+      { months: [9], action: "Dig sweet potatoes before frost", detail: "Vines die at the first touch of frost; cure warm (80–85°F) for a week to sweeten." },
+    ],
+  },
   {
     name: "Beet",
     family: "root",
@@ -387,13 +398,25 @@ function nameMatches(knowledgeName: string, plantName: string): boolean {
   return kStems.every((w) => pStems.includes(w));
 }
 
-/** The knowledge entry for a plant/type name, if we have one. */
+/**
+ * The knowledge entry for a plant/type name, if we have one. Prefers the most
+ * specific match: "Japanese sweet potato" must hit Sweet potato, not Potato.
+ */
 export function knowledgeFor(plantName: string): CropKnowledge | null {
+  let best: CropKnowledge | null = null;
+  let bestScore = 0;
   for (const crop of KNOWLEDGE) {
-    if (nameMatches(crop.name, plantName)) return crop;
-    if (crop.aliases?.some((a) => nameMatches(a, plantName))) return crop;
+    const names = [crop.name, ...(crop.aliases ?? [])];
+    for (const n of names) {
+      if (!nameMatches(n, plantName)) continue;
+      const score = norm(n).split(" ").filter(Boolean).length; // matched words
+      if (score > bestScore) {
+        best = crop;
+        bestScore = score;
+      }
+    }
   }
-  return null;
+  return best;
 }
 
 export type MonthlySuggestion = {
@@ -411,11 +434,14 @@ export function tipsForMonth(month: number, ownedNames: string[]): MonthlySugges
   const out: MonthlySuggestion[] = [];
   const seen = new Set<string>();
 
+  // Resolve each owned name to its single best crop, so "Sweet potato"
+  // doesn't also drag in regular Potato advice.
+  const grownCrops = new Set(
+    ownedNames.map((n) => knowledgeFor(n)?.name).filter((n): n is string => !!n),
+  );
+
   for (const crop of KNOWLEDGE) {
-    const grown = ownedNames.some(
-      (n) => nameMatches(crop.name, n) || crop.aliases?.some((a) => nameMatches(a, n)),
-    );
-    if (!grown) continue;
+    if (!grownCrops.has(crop.name)) continue;
     for (const tip of crop.tips) {
       if (!tip.months.includes(month)) continue;
       const key = `${crop.name}|${tip.action}`;
diff --git a/src/lib/version.ts b/src/lib/version.ts
index aa50d98..9f6c643 100644
--- a/src/lib/version.ts
+++ b/src/lib/version.ts
@@ -1,2 +1,2 @@
 // Bump on every user-visible release. Changelog entries live in `src/lib/changelog.ts`.
-export const APP_VERSION = "0.27.0";
+export const APP_VERSION = "0.28.0";