Sunday, April 17, 2011

Bullet-proof container design

Two months later! In hindsight I should have
clipped away some of the trailing silver falls
so you could see the pot and better
appreciate the color theme.
My design for Fine Gardening magazine
Just planted; a tropical Cordyline and
silver falls in a sleek, metal container. I
used black metallic glass beads to cover
the soil surface adding to the
contemporary vibe. 

While working in a retail nursery a few years ago, I was asked by a customer what plants could be used in a hanging basket if she was going to be away most of the summer. I had to keep my dry British humor in check… I mean come on. First of all what is the point in planting a basket in the first place if you’re not even going to be at home? Then there is the small matter of water. Even drought tolerant plants aren’t camels. She was quite upset when I had to tell her that there really wasn’t a solution (apart from silk) and I’m sure she went away thinking I was less than knowledgeable and that she would find someone to sell her something.

Do you find yourself watering-challenged when it comes to container gardens? Do your containers look decidedly sad before the summer is even part way through? Several factors can play into this from forgetfulness, to shady spots under eaves to cigarette butts! The latter is quite a serious problem for store fronts and public spaces and whereas we can’t do much about it apart from providing an ash tray, there are a few plants which can tolerate less than hospitable conditions. However let’s be clear that we are talking about low water use – not NO water! All plants need watering well when they are first planted.
Lavender revels in the heat
The first thing to consider is your choice of container and potting soil. The bigger the container, the less frequently it will need watering. Metal is a poor insulator and gets red-hot in full sun so isn’t a good choice for these situations. Terracotta is porous so draws the water out of the potting soil – also not desirable! Thick walled lightweight or ceramic pots are the best option.

Potting soil comes in many guises and they are most definitely not all equal. In fact I custom mix my potting medium every time because I simply have not found one single product which provides the perfect balance of organic matter and free draining material. For the typical mix of shrubs, perennials and annuals I’ll use approximately 80% soil-less potting mix which has plenty of perlite in it. Perlite is a popped volcanic rock that looks like tiny white lumps in good potting soil. It creates air spaces in the medium allowing water to drain freely. To this I’ll add 20% of organic matter; either bagged compost or one of the commercially available mixes of compost, mycorrhizae, earthworm castings and a little perlite. My current favorite is Gardner & Bloome ‘Blue Ribbon potting soil’. See notes below for occasional changes to this ratio though.

Hot stuff!

Containers which get full southern or western exposure have it tough. Reflective heat from bright surfaces such as light colored siding and concrete paths exacerbate the situation. Throw into that mix amnesia on the part of the homeowner and you know that these plants need to be real survivors.

Perhaps your immediate response is to add water retention crystals to the potting mix and at least one commercial potting soil does already contain these. However I’m a control freak when it comes to container design and I don’t want some inanimate polymer telling me how much water a container needs on any given day. I prefer to take the approach ‘right plant, right place’, just as we are encouraged to do in our gardens. A hot sunny location is simply not the place for ultra-thirsty plants which will wilt if not watered once or twice a day. Instead look to nature and choose instead those plants which thrive in our warmer climates.

Succulents come in an amazing assortment of colors and textures, many of which are fully hardy here in the Pacific Northwest (Zones 6-8) although I do love to supplement these with some of the more tender varieties for summer interest too. A simple container with a drought tolerant spiky Yucca, Dracaena, New Zealand flax (Phormium) or Cordyline surrounded by assorted mounding and trailing succulents makes an easy care design with great color and textural interest. Purple fountain grass is amazingly bullet proof too and I love the movement of its burgundy stems and plumes as a counterpoint to the fleshy succulent foliage. Succulents need exceptionally well drained soil and very little organic matter so this is a case where I decrease the compost component to just 5-10% and even add extra perlite to the potting mix. Incidentally this is a prime example of when you do not want any water retention polymers present.
Both the Sedum 'Blaze of Fulda' and silverbush are
reliably drought tolerant in hot sunny locations. Notice
how the sedum picks up on the color of the flower buds.
My design

Silver foliage often clues us in to the drought tolerance of plants. Lavender, silverbush (Convolvulus cneorum), curry plant (Helichrysum italicum) and Senecio ‘Sunshine’ (Senecio greyi syn. Brachyglottis greyi) all fit into this category. I love the silverbush as its leaves are glossy, sparkling in the sun as it reflects light from its shiny leaves. All these plants invite a closer look whether to enjoy the fragrance of flowers and crushed leaves (lavender and curry plant) or to feel them; Senecio has white felted undersides to its silvery leaves for example. If you really want the tactile factor add in some lambs ears (Stachys byzantina) and try to stop yourself from stroking those velvety leaves. These plants also like a very ‘lean’ and well drained soil so I prepare the potting mix as described for the succulents above.

What about color? In strong sunlight pastel colors look washed out so look for deeper shades of your favorite pink and lavender, taking them to magenta and purple. Red, orange and yellow all look right at home in sunny containers too. For height you could use a columnar barberry such as ‘Orange rocket’ (Berberis thunbergii) which offers orange tipped golden leaves in summer, orange fall color and tiny red berries. For lots of color in the middle of a design check out the indoor plant section of your nursery and pick up a Kalanchoe, available in orange, red, yellow or pink. These are unbelievably tough and bloom for months with minimal care. Lantana is a great summer annual for the front of containers often having multi-colored flowers. I love ‘Dallas red’ with its vibrant fiery tones. Some flowers are specifically grown for drying, such as strawflower (Helichrysum bracteatum) and annual borage (Echium plantagineum). Nurseries may not carry these until mid summer but they are easy to grow from seed on a windowsill. These provide a new stiff, papery texture as well as fresh color.
Although not intended as a 'bullet-proof' design, almost all
these plants are extremely easy going. The upright purple
 barberry 'Helmond's pillar' and its golden cousin 'Orange
nugget' provide height and bask in the sun. The mounding
'Blue star' junipers form an equally drought tolerant mid
point. Only the orange and purple 'million bells' tumbling
over the front edge insist on regular water.
My design

Shady spots.

I like sunshine – just my personality. When we go camping I look for a big open space rather than the shaded spots in the forest. Some plants just have to live with the shade however, because that’s where the containers are. Designing plants for shady corners isn’t difficult at all. The challenge is a shady spot that rarely gets watered! Shade can be due to overhanging trees, enclosed porches or a combination of both. A couple of my clients have tested my ‘bullet-proof’ shady plant list to the limit on more than one occasion and I dedicate this post to them. (You know who you are…).That being said I have to assume that everything in their containers is an ‘annual’ unless by some miracle they don’t kill it within 12 months in which case it earns Superstar status.
The stunning April foliage of Bishops hat 
(Epimedium rubrum)

Most shade loving plants do prefer regular water and we can at least help accommodate that by ensuring that the soil mix includes 20-25% organic material as discussed earlier. This will help retain what moisture there is! However on the whole I select plants which naturally grow in dry shade.

One of the best for color and hardiness is Aucuba with its brightly variegated yellow and green leaves. I’ve seen it survive everything from cigarettes to car exhaust. In fact lack of water seems to be the least of its problems! Having said that I did have to point out recently that its leaves were not supposed to droop downwards and that perhaps a gallon of water might be a good idea. (I suspect the pot hadn’t been watered for at least 4 weeks…)

Japanese aralia (Fatsia japonica) makes quite the tropical statement in the shade with its huge palmate leaves. It does surprisingly well with little care, making a striking focal point for a design. This does seem more susceptible to red spider mites when drought stressed however.

Although purple fountain grass is recommended above for full sun I have also used it in a container which gets no direct sun at all and it looks fabulous every summer. It might get a dribble of water every 2-3 weeks by the owner if it’s lucky!
A drought tolerant container garden
for the shade featuring Japanese
aralia, Bishop's hat, leucothoe
'Rainbow' and trailing vinca.
My design

Euonymus ‘Emerald gaiety’ and ‘Emerald ‘n’ gold’ (Euonymus fortunei) are tough shrubs which can be clipped to keep small or allowed to scramble into larger, looser shapes. They prefer sun in which case their color will be brighter. However they also tolerate a good deal of shade and watering once a week seems plenty. These work well as either ‘fillers’ or ‘spillers’ for container design depending on how you let them grow.

For the middle tier I have a surprising candidate for you; Heuchera ‘Tiramisu’. Don’t let its dainty appearance fool you. This has survived two of my most watering-challenged clients and they have done some serious testing I can assure you! Those beautiful lemon-yellow leaves marbled with terracotta veins look beautiful regardless of who looks after them.

Leucothoe ‘Rainbow’ features a lot in my designs for its year round interest, changing color, ease of maintenance and survival skills. Great for the center of large containers or cascading over the sides of smaller ones, its shades of green, yellow and red light up shady containers every time.

Another good candidate for cascading is the box honeysuckle (Lonicera nitida). There are several varieties from ‘Baggesens gold’ (bright green) to ‘Lemon beauty’ (variegated green and chartreuse). Although these can grow into huge shrubs they make good container specimens and are easy to prune as needed. I love pairing their finely textured leaves with the bolder hellebores.

Black mondo grass became the ‘American Idol’ of the plant world several years ago and for good reason. Evergreen strappy black foliage, lilac flowers followed by black berries and ease of propagation make this fun to add to baskets and containers as well as massing them as a groundcover in the landscape. They are also remarkably tolerant of drought.

So whereas I don’t advocate deliberately abusing your container gardens, you can at least select plants which will be more tolerant of less than perfect conditions. These are just a few possibilities; what have you had most success with?
A strappy New Zealand flax, fiery lantana
and variegated Abelia 'Tequila sunrise'
My design

Other plants for hot sites

Silver falls (Dichondra) (annual)
Licorice plant (Helichrysum petiolare) (annual)
Thyme (I love the golden and variegated forms)
Blue oat grass (Helictotrichon sempervirens)
Blue fescue grass (Festuca glauca)
Sea holly  (Eryngium)
Globe thistle (Echinops ritro)
Wormwood (Artemisia species)
Hyssop (Agastache)
Lavender cotton (Santolina chamaecyparissus)
Kangaroo paw (Anigozanthos)
Blue star juniper (Juniperus squamata)

Alternatives for dry shade

Hellebores (early spring flowers)
Sweet box (Sarcoccoca) (winter fragrance)
Aspidistra (good for height)
Woodrush (Luzula)
Bishops hat (Epimedium sp.)
Croton (light shade)

1 comment:

  1. Karen,

    I saw your Container Gardening article. I haven’t had a garden since my son was a teen, but I miss it now that he’s grown. We used to grow tomatoes and beans.

    Since you’ve written about containers, I wonder if your readers may like to see a video about container gardening:

    My name is Ed Hill and I’m working with gardening community to share links to their gardening videos.

    Plus, here’s a link to a 3 minute video about starting onions from seeds. You’re welcome to use this video in your blog, if you like: How to Grow Onions from Seeds
    Write me if you have any questions about the video. If you’re able to use this video, please let me know. My email is
    Thank you,
    Ed Hill


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