diff --git a/hub/db/db.py b/hub/db/db.py
index 23c87c3..6811dba 100644
--- a/hub/db/db.py
+++ b/hub/db/db.py
@@ -40,7 +40,7 @@ class SecondaryDB:
                  cache_all_claim_txos: bool = False, cache_all_tx_hashes: bool = False,
                  blocking_channel_ids: List[str] = None,
                  filtering_channel_ids: List[str] = None, executor: ThreadPoolExecutor = None,
-                 index_address_status=False):
+                 index_address_status=False, merkle_cache_size=32768):
         self.logger = logging.getLogger(__name__)
         self.coin = coin
         self._executor = executor
@@ -92,7 +92,7 @@ class SecondaryDB:
         # lru cache of tx_hash: (tx_bytes, tx_num, position, tx_height)
         self.tx_cache = LRUCacheWithMetrics(2 ** 15, metric_name='tx', namespace=NAMESPACE)
         # lru cache of block heights to merkle trees of the block tx hashes
-        self.merkle_cache = LRUCacheWithMetrics(2 ** 14, metric_name='merkle', namespace=NAMESPACE)
+        self.merkle_cache = LRUCacheWithMetrics(merkle_cache_size, metric_name='merkle', namespace=NAMESPACE)
 
         # these are only used if the cache_all_tx_hashes setting is on
         self.total_transactions: List[bytes] = []
diff --git a/hub/herald/db.py b/hub/herald/db.py
index 0f9a612..23692c1 100644
--- a/hub/herald/db.py
+++ b/hub/herald/db.py
@@ -9,10 +9,10 @@ class HeraldDB(SecondaryDB):
                  cache_all_claim_txos: bool = False, cache_all_tx_hashes: bool = False,
                  blocking_channel_ids: List[str] = None,
                  filtering_channel_ids: List[str] = None, executor: ThreadPoolExecutor = None,
-                 index_address_status=False):
+                 index_address_status=False, merkle_cache_size=32768):
         super().__init__(coin, db_dir, secondary_name, max_open_files, reorg_limit, cache_all_claim_txos,
                          cache_all_tx_hashes, blocking_channel_ids, filtering_channel_ids, executor,
-                         index_address_status)
+                         index_address_status, merkle_cache_size)
         # self.headers = None
 
     # async def _read_headers(self):
diff --git a/hub/herald/env.py b/hub/herald/env.py
index 104376f..7f43426 100644
--- a/hub/herald/env.py
+++ b/hub/herald/env.py
@@ -11,7 +11,8 @@ class ServerEnv(Env):
                  session_timeout=None, drop_client=None, description=None, daily_fee=None,
                  database_query_timeout=None, elastic_notifier_host=None, elastic_notifier_port=None,
                  blocking_channel_ids=None, filtering_channel_ids=None, peer_hubs=None, peer_announce=None,
-                 index_address_status=None, address_history_cache_size=None, daemon_ca_path=None):
+                 index_address_status=None, address_history_cache_size=None, daemon_ca_path=None,
+                 merkle_cache_size=None):
         super().__init__(db_dir, max_query_workers, chain, reorg_limit, prometheus_port, cache_all_tx_hashes,
                          cache_all_claim_txos, blocking_channel_ids, filtering_channel_ids, index_address_status)
         self.daemon_url = daemon_url if daemon_url is not None else self.required('DAEMON_URL')
@@ -53,6 +54,7 @@ class ServerEnv(Env):
         self.hashX_history_cache_size = address_history_cache_size if address_history_cache_size is not None \
             else self.integer('ADDRESS_HISTORY_CACHE_SIZE', 4096)
         self.daemon_ca_path = daemon_ca_path if daemon_ca_path else None
+        self.merkle_cache_size = merkle_cache_size if merkle_cache_size is not None else self.integer('MERKLE_CACHE_SIZE', 32768)
 
     @classmethod
     def contribute_to_arg_parser(cls, parser):
@@ -105,6 +107,10 @@ class ServerEnv(Env):
                             default=cls.integer('ADDRESS_HISTORY_CACHE_SIZE', 4096),
                             help="Size of the lru cache of address histories. "
                                  "Can be set in the env with 'ADDRESS_HISTORY_CACHE_SIZE'")
+        parser.add_argument('--merkle_cache_size', type=int,
+                            default=cls.integer('MERKLE_CACHE_SIZE', 32768),
+                            help="Size of the lru cache of merkle trees for txs in blocks. "
+                                 "Can be set in the env with 'MERKLE_CACHE_SIZE'")
 
     @classmethod
     def from_arg_parser(cls, args):
@@ -121,5 +127,6 @@ class ServerEnv(Env):
             database_query_timeout=args.query_timeout_ms, blocking_channel_ids=args.blocking_channel_ids,
             filtering_channel_ids=args.filtering_channel_ids, elastic_notifier_host=args.elastic_notifier_host,
             elastic_notifier_port=args.elastic_notifier_port, index_address_status=args.index_address_statuses,
-            address_history_cache_size=args.address_history_cache_size, daemon_ca_path=args.daemon_ca_path
+            address_history_cache_size=args.address_history_cache_size, daemon_ca_path=args.daemon_ca_path,
+            merkle_cache_size=args.merkle_cache_size
         )
diff --git a/hub/herald/service.py b/hub/herald/service.py
index 1ce9ecc..a792706 100644
--- a/hub/herald/service.py
+++ b/hub/herald/service.py
@@ -42,7 +42,7 @@ class HubServerService(BlockchainReaderService):
             env.coin, env.db_dir, self.secondary_name, -1, env.reorg_limit, env.cache_all_claim_txos,
             env.cache_all_tx_hashes, blocking_channel_ids=env.blocking_channel_ids,
             filtering_channel_ids=env.filtering_channel_ids, executor=self._executor,
-            index_address_status=env.index_address_status
+            index_address_status=env.index_address_status, merkle_cache_size=env.merkle_cache_size
         )
 
     def clear_caches(self):