Morningsun Herb Farm

The Mint Edition

Morningsun Herb Farm's newsletter for herbal enthusiasts

Spring/Summer 2009

Drought Tolerant Plants

by Rosemary Loveall-Sale

 

Each year brings new records for our California climate.  Record heat, cold, days without rain and number of fires have given us the dubious distinction of living in a place and time where the idea of ‘normal’  means  little.  Many of our customers are looking for plants and gardening ideas that will give them a lovely garden with as little water as possible.  The concept of a dry garden may be one that only includes prickly cactus, gray lifeless sparse foliage, flowers for only a few short weeks in the spring and lots of concrete and other hardscaping.   With proper attention to soil preparation, planting and watering techniques, a water wise garden can be attractive year round.

 

Of course, the plant material is the most exciting part of any garden plan, but a few details for soil preparation will save you the heartache of replanting, or of watching your plants languish as their root systems slowly try to establish under less ideal conditions.  So what is really needed for the soil to provide the best conditions for growth?   Most importantly, provide good drainage – add compost to the soil, mixing up to 6 inches of compost in the top 12 inches of topsoil.  Compost will increase drainage, increase air space for plant roots to respire and easily grow, and give a good substrate for microflora and fauna to live.  Heavy clay soils are generally poor for most drought tolerant perennials, which require excellent drainage for healthy root systems.

 

I usually stress never to add sand to a soil, especially if you are beginning with a heavy clay or clay loam that is commonly found here in Northern California.  Clay soil mixed with sand and dried in the hot California sun gives us the building blocks for California missions!  I would like to make some exceptions to that rule, given that more of the plants being grown in our gardens are native to very sandy or rocky soils.  Never use fine sand, such as builders sand or playground sand.  But with plants such as agaves, aloes and many other succulents, the addition of sharp sand and/or small gravel is more beneficial than compost alone.   Often for these plants are also mulched with a layer of gravel to keep the soil surface dry.

Second, your irrigation system should be able to water plantings deeply.  Drip irrigation systems are often used to ensure that only individual plants are watered, although spray heads or overhead watering can also be used.  The important thing with your choice of system is to be sure that plants can be watered deeply, especially when you are getting them established.  This will ensure that they are truly ‘drought tolerant’.   Many people will water often, but only provide enough water to penetrate the top several inches of soil.  This doesn’t offer the root system any reason to grow deeper, so it is essentially a ‘lazy’ plant, wilting quickly and producing little top growth.  Before planting, it is always a good idea to test water an area, turning on the irrigation system for a set time, then digging down to see how deeply the water has penetrated.  For healthy drought tolerant plants water should  penetrate at least a foot for short perennials and shrubs, and up to 3 feet for trees. 

 

Providing ample water early in the life of your garden will produce a large healthy deep root system that will be able to withstand extended periods of drought – often within a year plantings are able to not only survive but thrive with only weekly  irrigation, or often only bi-monthly irrigations.  This certainly is handy if you travel for your job and are away from home frequently, or go on vacation, or if watering restrictions are imposed in your community (a very real possibility this year).  Your landscaping can look beautiful and lush,  provide you with flowers and fragrance and bees, butterflies and hummingbirds with food and shelter with very little water input.

 

Planting time is also important when establishing  a drought tolerant garden.  First, it is important to take advantage of cooler temperatures and natural rainfall to help establish plants with the least amount of stress, both to the plant and to the planter!    For California natives and many other Mediterranean climate plants, this means early spring planting, or even late winter planting if that plant material is available.  Many Mediterranean plants have roots that are actively growing in late winter and early spring, and again in the mid to late fall, while they are naturally dormant, and therefore more difficult to establish, in the summer.  So plant as early as the soil allows (you don’t want to work to actively in very wet soils) and remember that if you miss the spring planting season, fall is a fabulous time to plant!

 

So, what about the fun part of planting?  What herbs and perennials can be grown in our Mediterranean climate with little watering and fuss?

 

Let’s begin with obvious drought tolerant plants in the mint family.  Lavender  is the most obvious choice, but with so many species and varieties, which would be the best selections for drought tolerant gardens? While all lavenders are considered drought tolerant and full sun loving, those that would be particularly tolerant of dry conditions are:  Lavandula ‘Silver Frost’, Lavandula ‘Goodwin Creek Grey’, Lavandula ‘Abrialii’, Lavandula ‘Grosso’, Lavandula ‘Gros Bleu’ and Lavandula dentata.  For the longest bloom, I would choose ‘Goodwin Creek Grey’, since it will bloom from April until November.  For cooking and crafting, ‘Grosso’, ‘Gros Bleu’ and ‘Abrialii’ are all excellent.  They are all great bee attractors and are fragrant. 

 

Sage is often used in the drought tolerant  garden, although it is important to note that many of the ‘New World’ sages prefer a bit more shade and water.  Some of the finest drought tolerant ‘New World’ sages are Salvia apiana, which is our Ca native white sage, and Salvia darcyii, which is a terrific hummingbird plant from northern Mexico.  It is large growing, to 3 feet tall and 5 feet wide, and   blooms from May until November.  Salvia clevelandii and Salvia mellifera  are California natives  that absolutely requires good drainage and little summer water to succeed.  Salvia leucantha, the common Mexican Bush Sage, is a terrific low water user that blooms from late summer until long into the winter in mild climates.   Salvia melissodora, or grape scented sage, is a large growing drought tolerant sage with flowers in the fall and spring that smell of grapes.  Salvia microphylla has deep red blooms topping reddish black stems with sticky leaves.  This plant is a bit of a rambler, growing to 3 feet tall and up to 5 feet wide as it spills out along the ground.  Much shorter is Salvia nemorosa ‘Caradonna’, which grows to only 1 foot tall with deep violet blue flower spikes.  Salvia chamaedryoides, or Electric blue sage, is a lovely short shrubby  evergreen.

 

One of my favorite African plants to grow in the drought tolerant garden is Lion’s Tail, or Leonotis leonurus.  This plant if fantastic for hummingbirds, with big whorls of deep orange blooms in sping, and from late summer through fall.  It can grow quite large, to 4 feet tall and as wide, and is very easily grown.  Alongside it I would grow the Hawaiian native Lepechinia hastata or false sage, which has large felted  fragrant  grey leaves and luscious violet blooms in the late summer and fall, and oddly for its origin, is extremely winter hardy and drought tolerant.   Salvia Africana-lutea is another stunning South African native with burnt orange flowers in the late winter.

 

There are quite a large number of terrific groundcovers to grow in very dry conditions.  My personal favorites are Thymus herba-barona, which is the very fragrant caraway thyme, and Thymus longicaulis, or turbo thyme.  Both of these thymes will grow rapidly in full sun or partial shade, with a minimum amount of water needed.   They are both long lived and require little care once established.  While they both have petty pink blooms, they are not very showy most of the year.  To add some color to a dry area, plant Achillea tomentosa ‘King Edward’, a low growing yarrow is with soft buttery yellow blooms.  Also, several of the Veronicas, both ‘Waterperry’ and pectinata, are excellent for providing plenty of periwinkle  blue blooms.  In areas where no foot traffic is planned, or near a very hot street or path, the ornamental oreganos are indispensable.  Origanum ‘Kent Beauty’ with long cascading lime green and pink blooms, Origanum dictamnus, with the same type of flowers and very furry gray foliage, or the more upright Origanum ‘Santa Cruz’, with sprays of soft pink blooms, can take intense sun and heat and will bloom all summer long.  Saponaria ocymoides, or common soapwort, is a low rambling plant that will bloom with lovely pink flowers from May until mid fall.  Scutellaria suffrutescens, or pink Texas skullcap, prefers hot dry weather, growing to only 10 inches tall, but 18 inches wide, with deep pink blooms all summer and fall.

 

Slightly taller groundcovers such as Nepeta ‘Walker’s Low’ with gray foliage and bright blue flowers, and many of the Achillea (yarrow), especially  ‘Moonshine’, with yellow blooms and gray foliage, and ‘Apple Blossom’, with soft green foliage and bicolored pink blooms.  Helianthemum nummularium ‘Double Red’ and ‘Sunfleck’ are both very tough evergreen groundcover with free blooming flowers.

 

Most plants that have silver or fuzzy foliage are more drought tolerant.  For example, lamb’s ears, or Stachys byzantina, are very furry and a silver white, and are extremely drought tolerant.  Also, Santolina chamaecyparissus ‘nana’ is a pungent scented short growing evergreen, perfect for a short border or for accent.  Artemesia ‘Powis Castle’ is a wide growing perennial that is extremely easy to grow – it can be slightly invasive if it is too happy!  Helichrysum italicum ‘nana’, or curry plant, is a very fragrant choice for an accent plant.  Marrubium incanum is very different from it’s ugly common horehound relative, with big wavy silvery leaves and bright pink flowers.  Ruta graveolens is a traditional medicinal plant with feathey grey foliage and yellow blooms. 

 

Following is a partial list of drought tolerant plants available at the nursery.  We have many more available and we are constantly adding new stock, so check the catalog for more information or to do a search on drought tolerant selections.

 

Groundcovers:

Achillea (yarrow) – all, especially Achillea tomentosa ‘King Edward’

Helianthemum nummularium

Hypericum x moserianum ‘Tricolor’ – for shade

Nepeta – all

Origanum – Dittany of Crete, Kent Beauty, golden, dwarf Greek

Rubus – creeping raspberry

Saponaria – soapwort

Sedum – most

Scutellaria

Sempervivum – most

Silene ‘Druett’s (partial shade)

Stachys (lambs ears)

Teucrium cossonii, marum,

Thymus – most, especially Elfin, turbo, caraway, wooly

Veronica ‘Waterperry’, pectinatus

 

Perennial, shrubs:

Agastache – especially ‘Firebird’, ‘Shaniko’, ‘Coronado’, ‘Apricot Sprite’, rupestris

Artemisia – especially wormwood, Powis Castle, French tarragon

Buddleia – all

Echinacea –  ‘Kim’s Knee High’

Euphorbia – especially myrsinites, ridida

Gaura – all

Helechrysum italicum, petiolare

Lantana – all

Lavandula – all

Leonotis leonurus

Lepechinia hastata

Linum (flax) – all

Lippia graveolens

Marrubium incanum, marum

Origanum – Santa Cruz, Italian, Hopley’s Purple

Pelargonium – most scented, sidoides

Penstemon – all

Phlomis – all

Rosemary – all, especially ‘Haifa’,

Rudbeckia – all, especially shorter varieties such as Rustic Colors

Salvia – argentea, apiana, Africana-lutea, canariensis, chamaedryoides, clevelandii, darcyi, fruticosa, greggii (all), leucantha, mellifera, melissodora, microphylla, nemorosa, officinalis, sclarea, semiatrata

Santolina – all

Sedum

Tagetes lemmonii, lucida

Teucrium chamaedrys, fruticans

Verbascum – most (some are weedy)