diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7e4ecb7f..28a92c77 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -11,8 +11,10 @@ jobs:
 
   test:
     name: Test (+${{ matrix.rust }}) on ${{ matrix.os }}
-    # The large timeout is to accommodate Windows builds
-    timeout-minutes: 75
+    # The large timeout is to accommodate:
+    # - Windows builds (75 minutes, typically 30-50 minutes)
+    # - parameter downloads (40 minutes, but only when the cache expires)
+    timeout-minutes: 115
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
@@ -87,7 +89,7 @@ jobs:
         uses: actions/cache@v2
         with:
           path: ${{ env.ZCASH_PARAMS }}
-          key: ${{ runner.os }}-params
+          key: ${{ runner.os }}-sprout-and-sapling-params
       - name: Fetch Zcash parameters
         if: steps.cache-params.outputs.cache-hit != 'true'
         working-directory: ./zebra-consensus
diff --git a/.github/workflows/coverage.yml b/.github/workflows/coverage.yml
index d713e02e..f1341778 100644
--- a/.github/workflows/coverage.yml
+++ b/.github/workflows/coverage.yml
@@ -13,8 +13,10 @@ jobs:
 
   coverage:
     name: Coverage (+nightly)
-    # The large timeout is to accommodate nightly builds
-    timeout-minutes: 60
+    # The large timeout is to accommodate:
+    # - nightly builds (75 minutes, typically 30-50 minutes)
+    # - parameter downloads (40 minutes, but only when the cache expires)
+    timeout-minutes: 115
     runs-on: ubuntu-latest
     env:
       CARGO_INCREMENTAL: 0
@@ -62,7 +64,7 @@ jobs:
         uses: actions/cache@v2
         with:
           path: ${{ env.ZCASH_PARAMS }}
-          key: ${{ runner.os }}-params
+          key: ${{ runner.os }}-sprout-and-sapling-params
       - name: Fetch Zcash parameters
         if: steps.cache-params.outputs.cache-hit != 'true'
         working-directory: ./zebra-consensus
diff --git a/Cargo.lock b/Cargo.lock
index db8068b8..2d9df883 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1086,7 +1086,7 @@ dependencies = [
 [[package]]
 name = "equihash"
 version = "0.1.0"
-source = "git+https://github.com/zcash/librustzcash.git?rev=53d0a51d33a421cb76d3e3124d1e4c1c9036068e#53d0a51d33a421cb76d3e3124d1e4c1c9036068e"
+source = "git+https://github.com/ZcashFoundation/librustzcash.git?rev=dea8d97d5ed09bdb6673cb64d0a63706f71c2f61#dea8d97d5ed09bdb6673cb64d0a63706f71c2f61"
 dependencies = [
  "blake2b_simd",
  "byteorder",
@@ -4181,7 +4181,7 @@ dependencies = [
 [[package]]
 name = "zcash_encoding"
 version = "0.0.0"
-source = "git+https://github.com/zcash/librustzcash.git?rev=53d0a51d33a421cb76d3e3124d1e4c1c9036068e#53d0a51d33a421cb76d3e3124d1e4c1c9036068e"
+source = "git+https://github.com/ZcashFoundation/librustzcash.git?rev=dea8d97d5ed09bdb6673cb64d0a63706f71c2f61#dea8d97d5ed09bdb6673cb64d0a63706f71c2f61"
 dependencies = [
  "byteorder",
  "nonempty",
@@ -4190,7 +4190,7 @@ dependencies = [
 [[package]]
 name = "zcash_history"
 version = "0.2.0"
-source = "git+https://github.com/zcash/librustzcash.git?rev=53d0a51d33a421cb76d3e3124d1e4c1c9036068e#53d0a51d33a421cb76d3e3124d1e4c1c9036068e"
+source = "git+https://github.com/ZcashFoundation/librustzcash.git?rev=dea8d97d5ed09bdb6673cb64d0a63706f71c2f61#dea8d97d5ed09bdb6673cb64d0a63706f71c2f61"
 dependencies = [
  "bigint",
  "blake2b_simd",
@@ -4200,7 +4200,7 @@ dependencies = [
 [[package]]
 name = "zcash_note_encryption"
 version = "0.0.0"
-source = "git+https://github.com/zcash/librustzcash.git?rev=53d0a51d33a421cb76d3e3124d1e4c1c9036068e#53d0a51d33a421cb76d3e3124d1e4c1c9036068e"
+source = "git+https://github.com/ZcashFoundation/librustzcash.git?rev=dea8d97d5ed09bdb6673cb64d0a63706f71c2f61#dea8d97d5ed09bdb6673cb64d0a63706f71c2f61"
 dependencies = [
  "blake2b_simd",
  "byteorder",
@@ -4215,7 +4215,7 @@ dependencies = [
 [[package]]
 name = "zcash_primitives"
 version = "0.5.0"
-source = "git+https://github.com/zcash/librustzcash.git?rev=53d0a51d33a421cb76d3e3124d1e4c1c9036068e#53d0a51d33a421cb76d3e3124d1e4c1c9036068e"
+source = "git+https://github.com/ZcashFoundation/librustzcash.git?rev=dea8d97d5ed09bdb6673cb64d0a63706f71c2f61#dea8d97d5ed09bdb6673cb64d0a63706f71c2f61"
 dependencies = [
  "aes",
  "bip0039",
@@ -4249,7 +4249,7 @@ dependencies = [
 [[package]]
 name = "zcash_proofs"
 version = "0.5.0"
-source = "git+https://github.com/zcash/librustzcash.git?rev=53d0a51d33a421cb76d3e3124d1e4c1c9036068e#53d0a51d33a421cb76d3e3124d1e4c1c9036068e"
+source = "git+https://github.com/ZcashFoundation/librustzcash.git?rev=dea8d97d5ed09bdb6673cb64d0a63706f71c2f61#dea8d97d5ed09bdb6673cb64d0a63706f71c2f61"
 dependencies = [
  "bellman",
  "blake2b_simd",
diff --git a/Cargo.toml b/Cargo.toml
index b621cd73..7732a6b8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -22,11 +22,21 @@ panic = "abort"
 
 [patch.crates-io]
 
-# TODO: replace with upstream orchard when these changes are merged
-# https://github.com/ZcashFoundation/zebra/issues/3056
+# TODO: replace with upstream orchard (#3056)
 orchard = { git = "https://github.com/ZcashFoundation/orchard.git", rev = "568e24cd5f129158375d7ac7d98c89ebff4f982f" }
 
-# TODO: remove these after a new librustzcash release.
+# TODO: replace with upstream librustzcash when these changes are merged (#3037)
+#
+# This zcash_proofs patch doesn't work, maybe because of features?
+#zcash_proofs = { git = "https://github.com/ZcashFoundation/librustzcash.git", rev = "dea8d97d5ed09bdb6673cb64d0a63706f71c2f61" }
+
+# Use the ZcashFoundation fork where possible, to avoid duplicate dependencies
+equihash = { git = "https://github.com/ZcashFoundation/librustzcash.git", rev = "dea8d97d5ed09bdb6673cb64d0a63706f71c2f61" }
+zcash_note_encryption = { git = "https://github.com/ZcashFoundation/librustzcash.git", rev = "dea8d97d5ed09bdb6673cb64d0a63706f71c2f61" }
+zcash_primitives = { git = "https://github.com/ZcashFoundation/librustzcash.git", rev = "dea8d97d5ed09bdb6673cb64d0a63706f71c2f61" }
+zcash_history = { git = "https://github.com/ZcashFoundation/librustzcash.git", rev = "dea8d97d5ed09bdb6673cb64d0a63706f71c2f61" }
+
+# TODO: remove these after a new librustzcash release (#2982)
 
 # These are librustzcash git requirements specified in its workspace Cargo.toml,
 # that we must replicate here
@@ -34,13 +44,15 @@ incrementalmerkletree = { git = "https://github.com/zcash/incrementalmerkletree.
 # Replaced by the ZcashFoundation fork above
 #orchard = { git = "https://github.com/zcash/orchard.git", rev = "2c8241f25b943aa05203eacf9905db117c69bd29" }
 
+# Replaced by the ZcashFoundation fork above
+
 # These are librustzcash file requirements specified in its workspace Cargo.toml,
 # that we must replace with git requirements
-zcash_note_encryption = { git = "https://github.com/zcash/librustzcash.git", rev = "53d0a51d33a421cb76d3e3124d1e4c1c9036068e" }
+#zcash_note_encryption = { git = "https://github.com/zcash/librustzcash.git", rev = "53d0a51d33a421cb76d3e3124d1e4c1c9036068e" }
 
 # These patches are not strictly required,
 # but they help avoid duplicate dependencies
-equihash = { git = "https://github.com/zcash/librustzcash.git", rev = "53d0a51d33a421cb76d3e3124d1e4c1c9036068e" }
-zcash_history = { git = "https://github.com/zcash/librustzcash.git", rev = "53d0a51d33a421cb76d3e3124d1e4c1c9036068e" }
-zcash_primitives = { git = "https://github.com/zcash/librustzcash.git", rev = "53d0a51d33a421cb76d3e3124d1e4c1c9036068e" }
-zcash_proofs = { git = "https://github.com/zcash/librustzcash.git", rev = "53d0a51d33a421cb76d3e3124d1e4c1c9036068e" }
+#equihash = { git = "https://github.com/zcash/librustzcash.git", rev = "53d0a51d33a421cb76d3e3124d1e4c1c9036068e" }
+#zcash_history = { git = "https://github.com/zcash/librustzcash.git", rev = "53d0a51d33a421cb76d3e3124d1e4c1c9036068e" }
+#zcash_primitives = { git = "https://github.com/zcash/librustzcash.git", rev = "53d0a51d33a421cb76d3e3124d1e4c1c9036068e" }
+#zcash_proofs = { git = "https://github.com/zcash/librustzcash.git", rev = "53d0a51d33a421cb76d3e3124d1e4c1c9036068e" }
diff --git a/zebra-chain/Cargo.toml b/zebra-chain/Cargo.toml
index b30c65a0..70f31bba 100644
--- a/zebra-chain/Cargo.toml
+++ b/zebra-chain/Cargo.toml
@@ -33,7 +33,6 @@ hex = "0.4"
 incrementalmerkletree = "0.1.0"
 jubjub = "0.8.0"
 lazy_static = "1.4.0"
-orchard = "0.0"
 rand_core = "0.6"
 ripemd160 = "0.9"
 secp256k1 = { version = "0.20.3", features = ["serde"] }
@@ -45,9 +44,15 @@ subtle = "2.4"
 thiserror = "1"
 uint = "0.9.1"
 x25519-dalek = { version = "1.2.0", features = ["serde"] }
-zcash_history = { git = "https://github.com/zcash/librustzcash.git", rev = "53d0a51d33a421cb76d3e3124d1e4c1c9036068e" }
-zcash_primitives = { git = "https://github.com/zcash/librustzcash.git", rev = "53d0a51d33a421cb76d3e3124d1e4c1c9036068e" }
-zcash_note_encryption = { git = "https://github.com/zcash/librustzcash.git", rev = "53d0a51d33a421cb76d3e3124d1e4c1c9036068e" }
+
+# TODO: replace with upstream orchard (#3056)
+orchard = { git = "https://github.com/ZcashFoundation/orchard.git", rev = "568e24cd5f129158375d7ac7d98c89ebff4f982f" }
+
+# TODO: replace with upstream librustzcash when these changes are merged (#3037)
+equihash = { git = "https://github.com/ZcashFoundation/librustzcash.git", rev = "dea8d97d5ed09bdb6673cb64d0a63706f71c2f61" }
+zcash_note_encryption = { git = "https://github.com/ZcashFoundation/librustzcash.git", rev = "dea8d97d5ed09bdb6673cb64d0a63706f71c2f61" }
+zcash_primitives = { git = "https://github.com/ZcashFoundation/librustzcash.git", rev = "dea8d97d5ed09bdb6673cb64d0a63706f71c2f61" }
+zcash_history = { git = "https://github.com/ZcashFoundation/librustzcash.git", rev = "dea8d97d5ed09bdb6673cb64d0a63706f71c2f61" }
 
 proptest = { version = "0.10", optional = true }
 proptest-derive = { version = "0.3.0", optional = true }
@@ -57,7 +62,6 @@ rand_chacha = { version = "0.3", optional = true }
 
 # ZF deps
 ed25519-zebra = "3.0.0"
-equihash = "0.1"
 # TODO: Update to 0.5 release when published
 redjubjub = { git = "https://github.com/ZcashFoundation/redjubjub.git", rev = "f772176560b0b7daf25eff2460e08dc127ac8407" }
 
diff --git a/zebra-consensus/Cargo.toml b/zebra-consensus/Cargo.toml
index 1fb4f266..c61b00a3 100644
--- a/zebra-consensus/Cargo.toml
+++ b/zebra-consensus/Cargo.toml
@@ -17,9 +17,6 @@ jubjub = "0.8.0"
 rand = "0.8"
 
 halo2 = "=0.1.0-beta.1"
-# TODO: replace with upstream orchard when these changes are merged
-# https://github.com/ZcashFoundation/zebra/issues/3056
-orchard = "0.0.0"
 
 chrono = "0.4.19"
 dirs = "4.0.0"
@@ -37,7 +34,11 @@ tower = { version = "0.4.11", features = ["timeout", "util", "buffer"] }
 tracing = "0.1.29"
 tracing-futures = "0.2.5"
 
-zcash_proofs = { git = "https://github.com/zcash/librustzcash.git", rev = "53d0a51d33a421cb76d3e3124d1e4c1c9036068e", features = ["local-prover", "multicore", "download-params"] }
+# TODO: replace with upstream orchard (#3056)
+orchard = { git = "https://github.com/ZcashFoundation/orchard.git", rev = "568e24cd5f129158375d7ac7d98c89ebff4f982f" }
+
+# TODO: replace with upstream librustzcash when these changes are merged (#3037)
+zcash_proofs = { git = "https://github.com/ZcashFoundation/librustzcash.git", rev = "dea8d97d5ed09bdb6673cb64d0a63706f71c2f61", features = ["local-prover", "multicore", "download-params"] }
 
 tower-fallback = { path = "../tower-fallback/" }
 tower-batch = { path = "../tower-batch/" }
diff --git a/zebra-consensus/src/chain.rs b/zebra-consensus/src/chain.rs
index 4e29f25a..58fe99b8 100644
--- a/zebra-consensus/src/chain.rs
+++ b/zebra-consensus/src/chain.rs
@@ -198,11 +198,13 @@ where
     S::Future: Send + 'static,
 {
     // Pre-download Groth16 parameters in a separate thread.
-    // This thread must be launched first, so the download doesn't happen on the startup thread.
 
+    // Give other tasks priority, before spawning the download task.
+    tokio::task::yield_now().await;
+
+    // The parameter download thread must be launched before initializing any verifiers.
+    // Otherwise, the download might happen on the startup thread.
     let groth16_download_handle = spawn_blocking(|| {
-        tracing::info!("checking if Zcash Sapling and Sprout parameters have been downloaded");
-
         // The lazy static initializer does the download, if needed,
         // and the file hash checks.
         lazy_static::initialize(&crate::groth16::GROTH16_PARAMETERS);
diff --git a/zebra-consensus/src/primitives/groth16/params.rs b/zebra-consensus/src/primitives/groth16/params.rs
index e3bb8bd6..a3cd8680 100644
--- a/zebra-consensus/src/primitives/groth16/params.rs
+++ b/zebra-consensus/src/primitives/groth16/params.rs
@@ -5,6 +5,13 @@ use std::path::PathBuf;
 use bellman::groth16;
 use bls12_381::Bls12;
 
+/// The timeout for each parameter file download, in seconds.
+///
+/// Zebra assumes that it's running on at least a 10 Mbps connection.
+/// So the parameter files should download in about 15 minutes using `zebrad download`.
+/// But `zebrad start` downloads blocks at the same time, so we allow some extra time.
+pub const PARAMETER_DOWNLOAD_TIMEOUT: u64 = 60 * 60;
+
 lazy_static::lazy_static! {
     /// Groth16 Zero-Knowledge Proof parameters for the Sapling and Sprout circuits.
     ///
@@ -20,10 +27,28 @@ lazy_static::lazy_static! {
 }
 
 /// Groth16 Zero-Knowledge Proof parameters for the Sapling and Sprout circuits.
-#[non_exhaustive]
 pub struct Groth16Parameters {
     /// The Sapling circuit Groth16 parameters.
     pub sapling: SaplingParameters,
+
+    /// The Sprout circuit Groth16 spend parameter.
+    pub sprout: SproutParameters,
+}
+
+/// Groth16 Zero-Knowledge Proof spend and output parameters for the Sapling circuit.
+pub struct SaplingParameters {
+    pub spend: groth16::Parameters<Bls12>,
+    pub spend_prepared_verifying_key: groth16::PreparedVerifyingKey<Bls12>,
+
+    pub output: groth16::Parameters<Bls12>,
+    pub output_prepared_verifying_key: groth16::PreparedVerifyingKey<Bls12>,
+}
+
+/// Groth16 Zero-Knowledge Proof spend parameters for the Sprout circuit.
+///
+/// New Sprout outputs were disabled by the Canopy network upgrade.
+pub struct SproutParameters {
+    pub spend_prepared_verifying_key: groth16::PreparedVerifyingKey<Bls12>,
 }
 
 impl Groth16Parameters {
@@ -33,9 +58,64 @@ impl Groth16Parameters {
     ///
     /// If the downloaded or pre-existing parameter files are invalid.
     fn new() -> Groth16Parameters {
-        Groth16Parameters {
-            sapling: SaplingParameters::new(),
+        let params_directory = Groth16Parameters::directory();
+        let sapling_spend_path = params_directory.join(zcash_proofs::SAPLING_SPEND_NAME);
+        let sapling_output_path = params_directory.join(zcash_proofs::SAPLING_OUTPUT_NAME);
+        let sprout_path = params_directory.join(zcash_proofs::SPROUT_NAME);
+
+        // TODO: instead of the path check, add a zcash_proofs argument to skip hashing existing files
+        //       (we check them on load anyway)
+        if !sapling_spend_path.exists() || !sapling_output_path.exists() {
+            tracing::info!("downloading Zcash Sapling parameters");
+            let new_sapling_paths =
+                zcash_proofs::download_sapling_parameters(Some(PARAMETER_DOWNLOAD_TIMEOUT))
+                    .unwrap_or_else(|error| {
+                        panic!(
+                            "error downloading Sapling parameter files: {:?}. {}",
+                            error,
+                            Groth16Parameters::failure_hint()
+                        )
+                    });
+            assert_eq!(sapling_spend_path, new_sapling_paths.spend);
+            assert_eq!(sapling_output_path, new_sapling_paths.output);
         }
+
+        if !sprout_path.exists() {
+            tracing::info!("downloading Zcash Sprout parameters");
+            let new_sprout_path =
+                zcash_proofs::download_sprout_parameters(Some(PARAMETER_DOWNLOAD_TIMEOUT))
+                    .unwrap_or_else(|error| {
+                        panic!(
+                            "error downloading Sprout parameter files: {:?}. {}",
+                            error,
+                            Groth16Parameters::failure_hint()
+                        )
+                    });
+            assert_eq!(sprout_path, new_sprout_path);
+        }
+
+        // TODO: if loading fails, log a message including `failure_hint`
+        tracing::info!("checking and loading Zcash Sapling and Sprout parameters");
+        let parameters = zcash_proofs::load_parameters(
+            &sapling_spend_path,
+            &sapling_output_path,
+            Some(&sprout_path),
+        );
+
+        let sapling = SaplingParameters {
+            spend: parameters.spend_params,
+            spend_prepared_verifying_key: parameters.spend_vk,
+            output: parameters.output_params,
+            output_prepared_verifying_key: parameters.output_vk,
+        };
+
+        let sprout = SproutParameters {
+            spend_prepared_verifying_key: parameters
+                .sprout_vk
+                .expect("unreachable code: sprout loader panics on failure"),
+        };
+
+        Groth16Parameters { sapling, sprout }
     }
 
     /// Returns the path to the Groth16 parameters directory.
@@ -51,52 +131,3 @@ impl Groth16Parameters {
         )
     }
 }
-
-/// Groth16 Zero-Knowledge Proof spend and output parameters for the Sapling circuit.
-#[non_exhaustive]
-pub struct SaplingParameters {
-    pub spend: groth16::Parameters<Bls12>,
-    pub spend_prepared_verifying_key: groth16::PreparedVerifyingKey<Bls12>,
-
-    pub output: groth16::Parameters<Bls12>,
-    pub output_prepared_verifying_key: groth16::PreparedVerifyingKey<Bls12>,
-}
-
-impl SaplingParameters {
-    /// Download if needed, cache, check, and load the Sapling Groth16 parameters.
-    ///
-    /// # Panics
-    ///
-    /// If the downloaded or pre-existing parameter files are invalid.
-    fn new() -> SaplingParameters {
-        // TODO: Sprout
-
-        let params_directory = Groth16Parameters::directory();
-        let spend_path = params_directory.join("sapling-spend.params");
-        let output_path = params_directory.join("sapling-output.params");
-
-        // Download parameters if needed.
-        //
-        // TODO: use try_exists when it stabilises, to exit early on permissions errors (#83186)
-        if !spend_path.exists() || !output_path.exists() {
-            tracing::info!("downloading Zcash Sapling parameters");
-            zcash_proofs::download_parameters().unwrap_or_else(|_| {
-                panic!(
-                    "error downloading parameter files. {}",
-                    Groth16Parameters::failure_hint()
-                )
-            });
-        }
-
-        // TODO: if loading fails, log a message including `failure_hint`
-        tracing::info!("checking and loading Zcash Sapling parameters");
-        let parameters = zcash_proofs::load_parameters(&spend_path, &output_path, None);
-
-        SaplingParameters {
-            spend: parameters.spend_params,
-            spend_prepared_verifying_key: parameters.spend_vk,
-            output: parameters.output_params,
-            output_prepared_verifying_key: parameters.output_vk,
-        }
-    }
-}
diff --git a/zebrad/src/commands/start.rs b/zebrad/src/commands/start.rs
index 338ff803..36b7d53e 100644
--- a/zebrad/src/commands/start.rs
+++ b/zebrad/src/commands/start.rs
@@ -19,6 +19,9 @@
 //!    * verifies blocks using zebra-chain, then stores verified blocks in zebra-state
 //!    * verifies mempool and block transactions using zebra-chain and zebra-script,
 //!      and returns verified mempool transactions for mempool storage
+//!  * Groth16 Parameters Download Task
+//!    * downloads the Sprout and Sapling Groth16 circuit parameter files
+//!    * finishes when the download is complete and the download file hashes have been checked
 //!  * Inbound Service
 //!    * handles requests from peers for network data, chain data, and mempool transactions
 //!    * spawns download and verify tasks for each gossiped block