I’ve just held a party on the main lawn in my garden. Over the last couple of months, in preparation for the event, I’ve been working away at planting, weeding and mulching this area. Well there is more I would have liked to have done, but the garden did provide a beautiful backdrop to celebrations and drew lots of favourable comments.
This is an area where I am focussing on hot colours – brilliant reds, oranges and yellows. The plants that drew the most attention from guests were the carpets of ornamental sweet potatoes. Their leaves were simply radiant. They really love the warmth, moisture and humidity we have been having and at this time of the year the leaves are larger, softer and more richly coloured than during the drier winter months. [Click on the photos for larger versions]
The simple green leafed and edible sweet potato (Ipomoea batatas) can make a great ground cover. I remember many years ago visiting clients on the Gold Coast who had progressively planted cuttings of the plant down a steep slope. Not only did it stabilise the area and prevent weed incursion, but it also provided a very attractive lush green backdrop. The plants could be progressively removed for future replanting – and it cost virtually nothing – in fact it provided free food.
Finding tubers on this scale can be tricky, in fact it can be tricky finding them in the vegie garden, however sweet potatoes furnish fantastic and nutritious ‘greens’. Younger leaves can be used in casseroles, stews, stir fries and curries. The youngest leaves and leaf buds are great in salads and add colour and textural variety. But try the leaves of the plant first. Some cultivars have sweet and tender leaves, whilst others are a little coarse and have a slightly strange flavour.
Ornamental sweet potatoes were first introduced to Australia in the early 1990s. While these cultivars continue to be popular overseas, they failed to attract much attention in this country and are no longer grown commercially. However they are worth looking out for. They include:
A favourite of mine with its large, brilliant chartreuse to butter yellow leaves (depending on the time of year), this plant is particularly robust and will cover a large area fairly readily. The plant was released by the Department of Horticulture New Crops Program at the University of Georgia in 1996 and was discovered in the Garden of a Mr Hunter Stubbs of Raleigh, North Carolina. Introduced into Australia soon after, it is probably most well known as the groundcover in the central Cairns traffic islands, thanks to inspired planting by landscape architect Anton Van der Schans. I suspect most plants originate from this source as I have never seen it for sale in a Queensland nursery, although it is now widely grown by keen gardeners.
This is a very vigorous blackish-purple leafed cultivar that was grown in North Queensland during the late 1990s. It is still very popular plant overseas. It has maple-like leaves and is a vigorous trailing cultivar.
‘Tricolor’ (‘Pink Frost’)
A stunning plant, it has grey-green leaves edged in pink. Popular overseas, I understand the plant is a little tender and may need a little protection over the cooler months.
I have been unable to track down these last two cultivars in recent years and would love to use them in my garden. I suspect they are still grown in north Queensland. If any reader grows them or knows a source, please contact me.
The recent interest in ornamental sweet potato plants has been due to the release of a number of new cultivars originating from breeding carried out at North Carolina State University. This programme focused on producing colourful compact plants. Cultivars Margarita and Blackie featured in some of the parentage. The Sweet Caroline Sweetheart series was first released in Australia in 2008.
As with many new plant introductions, there was very little information available regarding these plants and I fear that by the time the public cotton on to them, the plants will no longer be commercially available – a frequent occurrence in this country. Three cultivars were originally released:
‘Sweet Caroline Sweetheart Red’ (PBR)
My personal favourite. It has reddish-brown leaves and yellowish green new growth. The effect is a kaleidoscope of these colours and reminds me of a patchwork of fallen autumn leaves
‘Sweet Caroline Sweetheart Purple’ (PBR)
This plant has elongated purplish- black leaves which become very large during a warm, wet summer. It is the tallest growing and trailing of the cultivars.
‘Sweet Caroline Sweetheart Light Green’ (PBR)
Carrying pale, yellowish green heart shaped leaves, this cultivar is very dense and compact.
This year several new cultivars were released in Australia:
‘Sweet Caroline Purple’
The liquidamber shaped leaves and the stems are a purplish- black. The plant trails along the ground.
‘Sweet Caroline Bronze’
Probably the most rambling of these plants, the leaves are maple-like and a pale brown colour.
‘Sweet Caroline light Green’
A compact plant that forms a very dense cover. It has yellowish green maple-like leaves.
Sweet potatoes can be readily propagated by cuttings. During the summer months these can be simply planted insitu and they will establish rapidly. Note that The Sweet Caroline Sweetheart series is currently covered by the Australian Plant Breeder’s Rights (PBR) which provides the grower with exclusive rights to sell, produce, distribute and receive royalties from sales. This does however allow the purchaser to propagate the plant for their own use and these plants do look great mass planted as swards of colour in the landscape.
I find sweet potato plants are generally low maintenance, although they may require a bit of trimming over the summer months to keep them contained. They are virtually pest free. However there is one pest which can annihilate a bed – the bush turkey. They seem to discover a tuber and then progressively destroy the patch scraping plants away to find more. I always have a couple of patches of each cultivar, for the problem only seems to be bad in spring when the males need added sustenance to build their mounds. These are persistent creatures and once a turkey starts, there is little you can do to persuade it to go elsewhere.
Occasionally I get tiny holes in the leaves of some cultivars, but this seems to be short-term in nature and I suspect some predator insect moves in as these symptoms soon disappear.
Plants can be used in a variety of ways. In subtropical and tropical areas the plants are evergreen groundcovers and grow all year round being particularly vigorous over the warmer, wetter, summer months. In fact I need to prune them back this time of year or they will cover the lawn or nearby plantings. This can have an advantage where you want temporary cover – and plants can be readily composted.
Plants look great in large pots or hanging baskets with their distinctive trailing growth. Along with summer bedding, this is how they are generally grown in cooler climates, being treated as annuals.
Plants also complement various garden styles. The bold, brilliantly coloured leaves can be used to complement cordylines, heliconias, palms in a tropical inspired garden. They add colour and look spectacular in a potager or ornamental vegetable garden and are handy for incorporating in various dishes.
Consider plant partnerships. I have ‘Margartia’ next to Tradescantia pallida ’Purpurea’ and the contrasting, complementary colours simply sing to one another.
Some councils have strange views of this plant. I once helped Brisbane City Council write a brochure on hardy vegetables. Sweet potato was removed by the environmental section as they regarded all Ipomoea species as being potential weed species. As the sweet potato has been grown in the region for over 150 years, I suspect we would know its weed potential by now. It appears to be nil. I suspect the bush turkeys and bandicoots soon finish it off.
The BIG question I keep getting asked is do ornamental sweet potatoes produce edible tubers? Well yes they do….. but the tubers usually aren’t as large or regular as the ones we generally eat. They can be small, contorted and difficult to clean or peel. Look upon them as an additional bonus and dig them up just before you plan to use them so they are sweet and simply require a quick wash and trim…..and don’t forget the young leaves as they can provide a colourful garnish to a salad.
Want more foliage colour in the landscape? These could be the plants for you. What’s more they are lush and dense groundcovers that provide weed-free cover to garden beds and banks.