diff --git a/docs/changelog.txt b/docs/changelog.txt
index 0bd39e0cbd..b94cdce955 100644
--- a/docs/changelog.txt
+++ b/docs/changelog.txt
@@ -57,6 +57,8 @@ Template for new versions:
 
 ## Fixes
 - `getplants`: will no longer crash when faced with plants with growths that do not drop seeds when processed
+- `getplants`: use updated formula for calculating whether plant growths are ripe
+- `getplants`: fix logic for determining whether plant growths have been picked
 - `gui/teleport`: adapt to new behavior in DF 51.11 to avoid a crash when teleporting items into mid-air
 - `script-manager`: fix lua scripts in mods not being reloaded properly upon entering a saved world on Windows
 
@@ -66,6 +68,7 @@ Template for new versions:
 ## Documentation
 
 ## API
+- ``Random`` module: added ``SplitmixRNG`` class, implements the Splitmix64 RNG used by Dwarf Fortress for "simple" randomness
 - ``Items::getDescription``: fixed display of quality levels, now displays ALL item designations (in correct order) and obeys vanilla SHOW_IMP_QUALITY setting
 
 ## Lua
diff --git a/library/include/modules/Random.h b/library/include/modules/Random.h
index 38fbdd0f89..8ed703be79 100644
--- a/library/include/modules/Random.h
+++ b/library/include/modules/Random.h
@@ -106,6 +106,37 @@ namespace Random
     extern template void DFHACK_IMPORT MersenneRNG::unitvector<double>(double *p, int size);
 #endif
 
+    // Standard Splitmix64 RNG, as used by Dwarf Fortress's "hash_rngst" class
+    class SplitmixRNG
+    {
+        uint64_t state;
+
+    public:
+        SplitmixRNG(uint64_t seed) {
+            init(seed);
+        }
+
+        void init(uint64_t seed) {
+            state = seed;
+        }
+
+        uint64_t next() {
+            state += 0x9e3779b97f4a7c15;
+            uint64_t z = state;
+            z ^= z >> 30;
+            z *= 0xbf58476d1ce4e5b9;
+            z ^= z >> 27;
+            z *= 0x94d049bb133111eb;
+            z ^= z >> 31;
+            return z;
+        }
+
+        int32_t df_trandom(uint32_t max) {
+            uint32_t val = next() >> 32;
+            return (int32_t)(val % max);
+        }
+    };
+
     /*
      * Classical Perlin noise function in template form.
      * http://mrl.nyu.edu/~perlin/doc/oscar.html#noise
diff --git a/plugins/getplants.cpp b/plugins/getplants.cpp
index ab8333e51a..29c6655fc9 100644
--- a/plugins/getplants.cpp
+++ b/plugins/getplants.cpp
@@ -5,6 +5,7 @@
 #include "modules/Designations.h"
 #include "modules/Maps.h"
 #include "modules/Materials.h"
+#include "modules/Random.h"
 
 #include "df/map_block.h"
 #include "df/map_block_column.h"
@@ -211,32 +212,31 @@ selectability selectablePlant(color_ostream& out, const df::plant_raw* plant, bo
 }
 
 //  Formula for determination of the variance in plant growth maturation time, determined via disassembly.
-//  The x and y parameters are in tiles relative to the embark.
-bool ripe(int32_t x, int32_t y, int32_t start, int32_t end) {
-    int32_t time = (((435522653 - (((y + 3) * x + 5) * ((y + 7) * y * 400181475 + 289700012))) & 0x3FFFFFFF) % 2000 + *cur_year_tick) % 403200;
+//  The coordinates are relative to the embark region.
+bool ripe(int32_t x, int32_t y, int32_t z, int32_t start, int32_t end) {
+    DFHack::Random::SplitmixRNG rng((world->map.region_x * 48 + x) + (world->map.region_y * 48 + y) * 10000 + (world->map.region_z + z) * 100000000);
+    int32_t time = (rng.df_trandom(2000) + *cur_year_tick) % 403200;
 
     return time >= start && (end == -1 || time <= end);
 }
 
-//  Looks in the picked growths vector to see if a matching growth has been marked as picked.
-bool picked(const df::plant* plant, int32_t growth_subtype) {
-    df::world_data* world_data = world->world_data;
-    df::world_site* site = df::world_site::find(plotinfo->site_id);
-    int32_t pos_x = site->global_min_x + plant->pos.x / 48;
-    int32_t pos_y = site->global_min_y + plant->pos.y / 48;
-    size_t id = pos_x + pos_y * 16 * world_data->world_width;
-    df::world_object_data* object_data = df::world_object_data::find(id);
-    if (!object_data) {
+//  Looks in the local creation zone's picked growths vector to see if a matching growth has been marked as picked.
+bool picked(const df::plant* plant, int32_t growth_subtype, int32_t growth_density) {
+    int32_t pos_x = plant->pos.x / 48 + world->map.region_x;
+    int32_t pos_y = plant->pos.y / 48 + world->map.region_y;
+    size_t cz_id = pos_x + pos_y * 16 * world->world_data->world_width;
+    auto cz = df::world_object_data::find(cz_id);
+    if (!cz) {
         return false;
     }
-    df::map_block_column* column = world->map.map_block_columns[(plant->pos.x / 16) * world->map.x_count_block + (plant->pos.y / 16)];
-
-    for (size_t i = 0; i < object_data->picked_growths.x.size(); i++) {
-        if (object_data->picked_growths.x[i] == plant->pos.x &&
-            object_data->picked_growths.y[i] == plant->pos.y &&
-            object_data->picked_growths.z[i] - column->z_base == plant->pos.z &&
-            object_data->picked_growths.subtype[i] == growth_subtype &&
-            object_data->picked_growths.year[i] == *cur_year) {
+
+    for (size_t i = 0; i < cz->picked_growths.x.size(); i++) {
+        if (cz->picked_growths.x[i] == (plant->pos.x % 48) &&
+            cz->picked_growths.y[i] == (plant->pos.y % 48) &&
+            cz->picked_growths.z[i] == (plant->pos.z + world->map.region_z) &&
+            cz->picked_growths.density[i] >= growth_density &&
+            cz->picked_growths.subtype[i] == growth_subtype &&
+            cz->picked_growths.year[i] == *cur_year) {
             return true;
         }
     }
@@ -310,8 +310,8 @@ bool designate(color_ostream& out, const df::plant* plant, bool farming) {
         }
 
         if ((!farming || seedSource) &&
-            ripe(plant->pos.x, plant->pos.y, plant_raw->growths[i]->timing_1, plant_raw->growths[i]->timing_2) &&
-            !picked(plant, i))
+            ripe(plant->pos.x, plant->pos.y, plant->pos.z, plant_raw->growths[i]->timing_1, plant_raw->growths[i]->timing_2) &&
+            !picked(plant, i, plant_raw->growths[i]->density))
             return Designations::markPlant(plant);
     }