How to stack up multiple subcommands and have an implied default command using argparse?

In my example below, I am trying to setup the following command line scenarios:

$ myapp.py flowers [-h]
$ myapp.py flowers plants [-h]
$ myapp.py flowers plants add [-h]

The actual outcomes are:

$ python myapp.py flowers
usage: myapp.py flowers [-h] {plants} ...
myapp.py flowers: error: too few arguments
$ python myapp.py flowers plants
usage: myapp.py flowers plants [-h] [--format {plain,json}] {add} ...
myapp.py flowers plants: error: too few arguments
$ python myapp.py flowers plants add
Adding flowers...  The input format is expected to be plain

The problem is the second scenario. I intend for it to be an implicit "list" operation. How to do this?

Here is the source code to my example.

import sys
import argparse

def _flowers_plants_list(args):
    print('if this were real, the output format would be %s' % (args.format))       
    print('Here are all the flowers:')
    print('flower 1: rose')
    print('flower 2: tulip')
    print('flower 3: daisy')

def _flowers_plants_add(args):
    print('Adding flowers...  The input format is expected to be %s' % (args.format))

def main():
    # myapp.py
    parser_main = argparse.ArgumentParser()
    subparsers_main = parser_main.add_subparsers()

    # myapp.py flowers [-h]
    parser_flowers = subparsers_main.add_parser("flowers")
    subparsers_flowers = parser_flowers.add_subparsers()

    # (this is supposed to be an implicit list - NOT WORKING)
    # myapp.py flowers plants [-h]
    parser_flowers_plants = subparsers_flowers.add_parser("plants")
    parser_flowers_plants.add_argument("--format", default='plain', choices=['plain', 'json'], help="what format should the result be in")
    parser_flowers_plants.set_defaults(func=_flowers_plants_list)
    subparsers_flowers_plants = parser_flowers_plants.add_subparsers()

    # myapp.py flowers plants add [-h]
    parser_flowers_plants_add = subparsers_flowers_plants.add_parser("add")
    parser_flowers_plants_add.add_argument("--format", default='plain', choices=['plain', 'json'], help="what format will the input be in")
    parser_flowers_plants_add.set_defaults(func=_flowers_plants_add)

    args = parser_main.parse_args()
    r = args.func(args)
    return r

if __name__ == "__main__":
    sys.exit(main())