I recently read a book called The Dry Gardening Handbook by Olivier Filippi. He explains how he has gardened for decades, choosing plants that need no irrigation. He profiles many plants and gives them a rating based on how many months they can withstand drought: a “5” means the plant can withstand five months without rain or irrigation. If you’ve ever been frustrated by a book or catalog that called a plant “xeric” or “drought tolerant” only to find out the plant can’t survive a week without irrigation, you might find this book interesting. His ratings go from one to six, with six (six months!) being the most drought tolerant.
He gardens in France, in a Mediterranean climate, where it is rainy in the winter and very dry in the summer. This is different from Colorado, not only in the pattern of moisture, but in our much lower temperatures. Nonetheless, in his list are many plants that are hardy along the Front Range of Colorado. I’m listing some of the hardiest ones with his ratings to let you compare the drought tolerance of one species with another. Maybe you’ll be as surprised as I was to see some of the plants that received a 4 or 5.
This book has inspired many discussions with my gardening friends. I recommend reading it if you can find it for a reasonable price. For some reason it has gone up a lot since my friend Donna bought it and loaned it to me!
Plant Name Drought Code
Achillea millefolium (Yarrow) 2.5
Achnatherum calamagrostis (Silver Spike Grass) 4
Alcea rosea (Hollyhock) 3
Antirrhinum hispanicum (Snapdragon) 5
Artemisia ludoviciana 3
Artemisia dracunculus (French tarragon) 2.5
Asphodelus albus 4
Buddleia alternifolia (Silver Butterfly Bush) 3.5
Buxus sempervirens (Boxwood) 4
Campsis radicans (Trumpet Vine) 3
Caryopteris x clandonensis (Blue Mist Spirea) 2.5
Catananche caerulea (Cupid’s Dart) 4
Centranthus ruber (Red Valerian, Jupiter’s Beard) 4
Cerastium tomentosum 2
Cerastistigma plumbaginoides 3.5
Cotinus coggyrgria (Smoke Bush) 4
Crocus sativus 5
Delosperma cooperi 4
Echinops ritro 3
Eryngium amethystinum (Sea Holly) 4
Eschscholzia californica (CA Poppy) 5
Festuca glauca ‘Elijah Blue’ 2
Gaura lindheimeri 4
Geranium sanguineum (Cranesbill) 4
Helianthemum–many cultivars (Sunrose) 2.5
Helianthus maximiliani (New Mexico Sunflower) 4
Helichrysum italicum (Curry Plant) 4
Hesperaloe parvilora (Red Yucca) 6
Iris germanica (Bearded Iris) 5
Juniperus horizontalis (Creeping Juniper) 4
Kniphofia ‘Geant’ (Red Hot Poker) 3
Lavandula angustifolia (Lavender) 3
Lavandula x intermedia (Lavender) 4
Nepeta x faassenii ‘Six Hills Giant’ (Catmint) 3.5
Nepeta cataria (Catnip) 2.5
Oenothera macrocarpa (Evening Primrose) 5
Origanum laevigatum (Ornamental Oregano) 4
Origanum majorana (Marjoram) 4
Origanum onites (Italian or Cretan Oregano) 5
Origanum heracleoticum (Greek Oregano) 3
Perovskia atriplicifolia (Russian Sage) 4
Ruta graveolens (Rue) 4
Salvia greggii (Red-flowered Sage) 4
Salvia sclarea (Clary Sage) 4
Salvia darcyi 4
Salvia officinalis (Culinary Sage) 2
Santolina chamaecyparissus (Lavender Cotton) 5
Satureja montana (Winter Savory) 3.5
Sedum album 4
Sedum sediforme 5
Sempervivum tectorum (House Leek, Hen & Chicks) 3
Sphaerakcea ambigua 6
Stachys byzantina (Lamb’s Ears) 3
Teucrium cossonii (Majorca Germander) 4
Teucrium chamaedrys (Germander) 4
Thymus vulgaris (Common Thyme) 4
Thymus serpyllum (Creeping thyme) 2
Vinca major 2.5
Vinca minor 3
Zauschneria garrettii (CA Fuchsia) 4
