Create a systemd service file:

/etc/systemd/service/garden-lights.service

[Unit]
Description=Scheduler to turn garden lights on / off
After=network.target

[Service]
User=<username>
WorkingDirectory=/<path>/garden_lights/app/
ExecStart=/<path>/.local/bin/gunicorn -b 0.0.0.0:8000 -w 4 'app:create_app()''
Restart=always

[Install]
WantedBy=multi-user.target

# systemctl daemon-reload 
# systemctl start garden-lights.service