diff --git a/.github/workflows/tests.yaml b/.github/workflows/tests.yaml
index 0114a5f..f935833 100644
--- a/.github/workflows/tests.yaml
+++ b/.github/workflows/tests.yaml
@@ -7,6 +7,7 @@ on:
 jobs:
   test:
     runs-on: ${{ matrix.os }}
+    continue-on-error: ${{ matrix.experimental }}
     strategy:
       fail-fast: false
       matrix:
@@ -15,22 +16,32 @@ jobs:
             python: "3.10"
             os: ubuntu-latest
             toxenv: py310
+            experimental: false
           - name: Test suite with py311-ubuntu
             python: "3.11"
             os: ubuntu-latest
             toxenv: py311
+            experimental: false
+          - name: Test suite with py312-ubuntu
+            python: "3.12-dev"
+            os: ubuntu-latest
+            toxenv: py312
+            experimental: true
           - name: Type check with mypy
             python: "3.10"
             os: ubuntu-latest
             toxenv: type
+            experimental: false
           - name: Formatting with black + isort
             python: "3.10"
             os: ubuntu-latest
             toxenv: format
+            experimental: false
           - name: Linting with flake8 + ruff
             python: "3.10"
             os: ubuntu-latest
             toxenv: lint
+            experimental: false
 
     name: ${{ matrix.name }}
     env:
diff --git a/pyproject.toml b/pyproject.toml
index c16a3b9..16fa028 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -69,7 +69,7 @@ pythonpath = ["src"]
 legacy_tox_ini = """
     [tox]
     requires = tox>=4
-    env_list = format, type, lint, py{310,311}
+    env_list = format, type, lint, py{310,311,312}
 
     [testenv]
     description = run unit tests
@@ -82,8 +82,8 @@ legacy_tox_ini = """
     basepython = python3.10
     extras = formatting
     commands =
-            black src
-            isort src
+            black src --check --verbose
+            isort src --check
 
     [testenv:type]
     description = run type checks
diff --git a/src/pedon/__init__.py b/src/pedon/__init__.py
index 5bc4911..6c647d2 100644
--- a/src/pedon/__init__.py
+++ b/src/pedon/__init__.py
@@ -5,6 +5,7 @@
 from .soil import Soil as Soil
 from .soil import SoilSample as SoilSample
 from .soilmodel import Brooks as Brooks
+from .soilmodel import Gardner as Gardner
 from .soilmodel import Genuchten as Genuchten
 from .soilmodel import Panday as Panday
 from .soilmodel import plot_hcf, plot_swrc
diff --git a/src/pedon/_version.py b/src/pedon/_version.py
index 81f0fde..b1a19e3 100644
--- a/src/pedon/_version.py
+++ b/src/pedon/_version.py
@@ -1 +1 @@
-__version__ = "0.0.4"
+__version__ = "0.0.5"
diff --git a/src/pedon/soilmodel.py b/src/pedon/soilmodel.py
index a0f6286..a57b733 100644
--- a/src/pedon/soilmodel.py
+++ b/src/pedon/soilmodel.py
@@ -3,7 +3,7 @@
 
 import matplotlib.pyplot as plt
 from numpy import abs as npabs
-from numpy import exp, full, linspace, log, logspace, log10
+from numpy import exp, full, linspace, log, log10, logspace
 
 from ._typing import FloatArray
 
@@ -201,6 +201,7 @@ class Panday:
     sr: float = field(init=False, repr=True)
     gamma: float = field(init=False, repr=False)  # 1 - 1 / beta
     sy: float = field(init=False, repr=False)
+    ss: float = field(default=1e-6, repr=False)
 
     def __post_init__(self):
         self.sr = self.theta_r / self.theta_s  # theta_r / theta_s
diff --git a/tests/test_soilmodel.py b/tests/test_soilmodel.py
index 2b97abc..60a6579 100644
--- a/tests/test_soilmodel.py
+++ b/tests/test_soilmodel.py
@@ -1,11 +1,13 @@
 import pytest
-from numpy import logspace
+from numpy import array, logspace
 
 import pedon as pe
 from pedon._typing import FloatArray
 
 h = -logspace(-2, 6, num=50)
 
+theta = array([0.1, 0.2, 0.3, 0.4])
+
 
 @pytest.fixture
 def gen() -> pe.soilmodel.SoilModel:
@@ -22,6 +24,11 @@ def sor() -> pe.soilmodel.SoilModel:
     return pe.Panday(k_s=10, theta_r=0.01, theta_s=0.43, alpha=0.02, beta=1.1, brook=3)
 
 
+@pytest.fixture
+def gar() -> pe.soilmodel.SoilModel:
+    return pe.Gardner(k_s=10, theta_r=0.01, theta_s=0.43, a=0.02, b=1.0, m=1.1)
+
+
 def test_theta_genuchten(gen: pe.soilmodel.SoilModel, h: FloatArray = h) -> None:
     gen.theta(h=h)
 
@@ -34,6 +41,10 @@ def test_k_genuchten(gen: pe.soilmodel.SoilModel, h: FloatArray = h) -> None:
     gen.k(h=h)
 
 
+def test_h_genuchten(gen: pe.soilmodel.SoilModel, theta: FloatArray = theta) -> None:
+    gen.h(theta=theta)
+
+
 def test_theta_brooks(bro: pe.soilmodel.SoilModel, h: FloatArray = h) -> None:
     bro.theta(h=h)
 
@@ -46,6 +57,10 @@ def test_k_brooks(bro: pe.soilmodel.SoilModel, h: FloatArray = h) -> None:
     bro.k(h=h)
 
 
+def test_h_brooks(bro: pe.soilmodel.SoilModel, theta: FloatArray = theta) -> None:
+    bro.h(theta=theta)
+
+
 def test_theta_panday(sor: pe.soilmodel.SoilModel, h: FloatArray = h) -> None:
     sor.theta(h=h)
 
@@ -56,3 +71,23 @@ def test_s_panday(sor: pe.soilmodel.SoilModel, h: FloatArray = h) -> None:
 
 def test_k_panday(sor: pe.soilmodel.SoilModel, h: FloatArray = h) -> None:
     sor.k(h=h)
+
+
+def test_h_panday(sor: pe.soilmodel.SoilModel, theta: FloatArray = theta) -> None:
+    sor.h(theta=theta)
+
+
+def test_theta_gardner(gar: pe.soilmodel.SoilModel, h: FloatArray = h) -> None:
+    gar.theta(h=h)
+
+
+def test_s_gardner(gar: pe.soilmodel.SoilModel, h: FloatArray = h) -> None:
+    gar.s(h=h)
+
+
+def test_k_gardner(gar: pe.soilmodel.SoilModel, h: FloatArray = h) -> None:
+    gar.k(h=h)
+
+
+def test_h_gardner(gar: pe.soilmodel.SoilModel, theta: FloatArray = theta) -> None:
+    gar.h(theta=theta)