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Container Gardening

By Janice Hardy

Haliburton County Master Gardener

Container Garden - Patio Planter

Even the smallest of spaces can enjoy the beauty of flowers or vegetables in well arranged containers.  Container gardening is about more than just filling a pot with a few plants.  It is about art in your garden, on your deck, on your balcony.  It is about understanding and using plant knowledge and applying design concepts to create an attractive, sophisticated garden in a container.  By considering composition using colour, form, and texture - containers can provide season long interest to any patio, deck and balcony or even those hard to fill spaces in the garden

The Container

Choosing the container is as important as choosing the plants.  I have selected an English style terra-cotta planter that is 24” wide at the top and narrows to 18” at the base.  The container is 18” deep.  The pot has five holes in the bottom to promote drainage.  The choice of this pot means that more care will be required to maintain the health of the plants.  Clay dries out more quickly as water evaporates more easily than from plastic or fiberglass containers and require more work to store during the winter months.  However, I felt the beauty of the pot over-rides the above concerns.  

The Media

The media I have chosen is Miracle-Gro potting mix with a enough available nutrients to get the plants started.  I have used this media in the past with great success.  The choice of a potting mix verses garden soil was made for a number of reasons.  Soil does not drain well in containers.  This leaves the potential of roots becoming soggy, reducing the oxygen availability to the roots and the decline in the health of the plant.  Potting mixes are sterilized to kill weeds seeds and pathogens, are generally pH balanced and have a small amount of nutrients available to young plants.  

I have chosen to cover the drainage holes with pot shards.  The use of gravel, which we often learned from our mothers was the appropriate thing to do, raises the water table of the pot, leading again to the problem of soggy roots and soil borne diseases.  By choosing to cover the holes in this way, the water table of the pot is equal to the bottom of the pot.  If desired, one could cover the holes with polystyrene packing peanuts enclosed in clean, onion netting.  This serves the dual purpose of containing the soil in the pot and lightening this heavy terra-cotta planter.  

To mitigate dryness due to evaporation from the clay pot, water-absorbing polymers were added to the soil mix.  When wet, these polymers hold up to 200 times their weight in water.  As the growing medium dries out, the polymers release the water for plant use.  This will help reduce the watering needs of the container, however it is important to check the planters daily for watering and disease or insect infestation.  

Another amendment to the media is slow release fertilizer in the ratio of 1:2:2.  Once the media is moist and the fertilizer has absorbed some water, soil temperature is the only factor that affects the long term release of the nutrients.  The label on the fertilizer should inform the gardener of the ideal release temperature.  Temperatures above the ideal will release the fertilizer more quickly and temperatures below the ideal will release the fertilizer more slowly than what is documented on the label.   Apply the fertilizer to the media at the recommended rate for the size of the pot.  Using a water-soluble fertilizer after the first three or four months may be needed to keep containers healthy and beautiful.  

Water is added to the potting mix to moisten the soil after the water-absorbing polymers and slow release fertilizer are added and before planting.  Potting mix can be quite dry coming out of the bag.  Water is added and mixed in to the media and let sit for one or two hours for full absorption.  

The Design

For the design, plants enjoying similar growing conditions are selected based on colour, shape and texture.  In terms of colour, analogous colours of yellow and orange that are next to each other on the colour wheel (see image right) are chosen with a splash of contrast to add some drama.  Colours include the harmonious hues of yellow rudbeckia and margarita daisy that with the orange canna flowers contrast with the dark purple leaves of sweet potato vine and the burgundy canna lily leaves.  The  ornamental grass with its finely textured green leaves and soft tan-coloured plumes adds texture to the appearance.  

In addition to the design principals outlined above, another key component to designing planters are what have become to be known as thrillers, fillers and spillers. The thriller is the focal point of the container that draws the eye and adds height.  Fillers make up the mid container space without distracting from the focal point.  Spillers are cascading plants that flow over the edge of the container and fill the spaces left after planting the fillers.  Plants with different or long blooming periods or that display distinctive foliage, some of which may change colour with the onset of fall, provides interest over the season.  

After filling the container to about two thirds full with media, arrange the plants as per the design.  The largest plant - the Canna - will be planted first, followed by the grass and then the filler and spiller plants using the remaining media.  Fill the container with the pre-moistened media to approximately 2.5 cm below the edge of the pot for water catchment.  As with the garden, plants should be planted no deeper than they are in the original pot.  

The plants include the following list with the Canna planted at the far edge of the container and the fountain grass beside it.  The Marguerite daisies are planted next is a semi circle around the specimen plants followed by the geraniums between and in front of the daisies.  The sweet potato vine is planted last and position such that it spills over the edge.

A:  Canna ‘Tropicanna’  (Tropicanna Canna) - 1 plant

B:  Pennisetum alopecuriodes ‘Hameln’ (Dwarf Fountain Grass) - 1 plant

C:  Argyranthemum frutescens ‘Butterfly’ (Marguerite Daisy) - 3 plants

D:  Pelargonium ‘Blood Red’ (Blood Red Geranium) - 3 plants

E:  Ipomoea batalas ‘Blackie’  (Sweet Potato Vine) - 3 plants

The Thrillers

It is important to consider the perspective or angle of view when planting the container.  In this instance the thrillers are placed close to the back of the planter and slightly off centre as the angle of view is about 280 degrees.  

Pennisetum alopecuriodes ‘Hameln’ (Dwarf Fountain Grass) has been selected as the focal point (image right).  This specimen is considered an annual in Haliburton although it is hardy to CDA zone 5 and some sites indicate it is cold hardy to zone 4.  It is a fine textured arching grass with green leaves and mid-summer tan-coloured blooms.  In full sun and moist, well-drained soil it will grow to about 80-90 cm (32-36”) tall.  

Canna ‘Tropicanna’ (Tropicanna Canna Lily) will add height to the arrangement (see image right).  Chosen for its broad leaves with green, burgundy, red and yellow stripes and brilliant orange flowers, this eye-catching specimen stands about 120 cm (48”) tall.  As with most Cannas, this specimen prefers full sun and rich, moist soils, especially during the active growing period.  For best flower development a higher potassium fertilizer in the ratio similar to the 1:2:2 added as an amendment is preferable.  The rhizomes are tender and will be started indoors at the beginning of April and transplanted to the container. 

The Fillers

The filler plants include three Marguerite Daisies and three red Geraniums.    

Argyranthemum frutescens ‘Butterfly’ (Marguerite Daisy ‘Butterfly).  A tender perennial in zone 9, this specimen is considered an annual in Ontario.  Growing to a height of 40-60 cm (16-26”), this gorgeous flower blooms late spring through to frost providing colour season over the entire season.  The bright green, deeply lobed fern-like leaves are fragrant when crushed and will add a fine texture and contrast to the container.  The flowers are bright yellow with golden-orange centres and complement both the geranium and canna.  

Pelargonium ‘Blood Red’.  An annual commonly known as geranium are used as bedding plants in Ontario.  Growing to a height of about 30-50 cm (12-16”) tall, these plants prefer full sun and rich well-drained soil.  Deadheading will promote blooming over the entire summer, adding rich colour to the container.  

The Spillers

Ipomoea batatas ‘Blackie’ (Sweet Potato Vine ‘Blackie’) (image right).  Chosen primarily for its foliage, this plant has stunning purple leaves that spill over the edges of the container trailing up to 150 cm.  It will add interest and contrast to the yellow flowers and green leaves of the filler plants.  Like the other container plants, sweet potato vine does well in full to part sun and moist, well drained soil.    


This container will need to be checked daily for watering needs although the water-absorbing polymers will keep the plants moist for a period of time.  Morning watering is best so that plant leaves have an opportunity to dry during the day thereby helping to avoid any disease problems.  Even in seasons with high rainfalls, containers still need to be watered as rarely is enough rain absorbed to meet the plants needs.  Water when the soil feels dry for a depth of 2.5 cm and if possible, try to avoid wetting the leaves.  

Because a slow release fertilizer was mixed into the media, additional fertilizer may not be required.  However with the hot summer temperatures in Ontario, the release of nutrients may be faster than anticipated.  My preference is to add a water-soluble fertilizer every four weeks during periods of rapid growth and bloom period.  Fertilizer applications will be reduced in the fall to ensure the perennials harden-off for the winter.  

Deadheading of spent flowers will encourage continuous blooms throughout the summer and keep the arrangement looking tidy.  Any damaged or diseased stems will need to be pruned out and some shaping may be required.  While deadheading, plants can be inspected for bugs and disease. 

Slugs, snails and earwigs can be picked off or treated with a pesticide.  Pelletized products work well in containers but may have to be replaced once every six weeks or so as they are water-soluble.  Aphids are another common problem in container plantings and can be sprayed off with water if the infestation is mild.  The use of an insecticidal soap on the undersides of leaves and on stems is also helpful.  

Some of the plants in this container can be overwintered.  The arrangement will be disassembled in early October so that the perennials will have an opportunity to establish themselves in the landscape before winter sets in.  

The Dwarf Fountain Grass will be planted in a sheltered area of the garden to see if it will overwinter in zone four.  The annuals will be discarded into the compost bin. 

The Canna rhizome will require a little more care.  The plant will be cut back to within 3 cm of the bulb after the first killing frost. The rhizome will be lifted, and leaving some soil around the clump, stored in a cool dry area in the basement. The rhizomes like to be moist, even when dormant. Inspect periodically and sprinkle with water if needed.  Rhizomes can be divided in the spring wherever there is more than one stem.  

The terra-cotta container needs to washed and dried and stored in the basement as it can freeze and crack in the cold winter weather.  Prior to planting in the spring, the pot should be washed again with soap and water, rinsed and sterilized using a 10% bleach solution.  


Bluestem Nursery:

Canadian Gardening Magazine:

Far East Plants Corporation:

Heritage Perennials:

Paul Zammit:  The Greenhouse Grower:

Plant Advice:

Proven Winners:

Dinah Wilson,
Jan 30, 2012, 10:01 AM