This summer so far has been warm and the intermittent rain has been good for the garden.
Like people, plants all react differently to the heat and some plants relish it.
In gardens where there is shelter from the wind, a hot microclimate ensues. This really encourages spectacular flowering in plants such as bougainvillea, mandevillea, silk trees, jacarandas, petunias, tropical impatiens, flame vine and tropical hibiscus. Driving around the city I have seen good examples of some of these. It is during the hot months that these plants really come into their own.
Other plants don't react well to the heat; hellebores, Chatham island forget-me-nots, rhododendrons, azaleas and camellias can all end up with scorching on their leaves from excessive sun if they are overly exposed.
The summer months can be a time when substantial growth can be made if plants are kept moist. If you are growing plants to create privacy, then ensuring they are well watered and well fertilised during the summer months will encourage much faster growth than during cooler times of the year. Plants such as pittosporum, griselinia and many other natives, evergreens and deciduous trees will react in this way.
A way to help plants during the summer months is to mulch the soil around them. Mulching is the spreading of a layer of organic matter on the surface of the soil with the aim to improve moisture retention, suppress weeds and provide a cooling effect on the soil and root system below.
Mulching will improve soil structure and encourage earthworms and microbial activity, giving better results for both new and existing plantings. As the saying goes "the answer lies in the soil" in regards to success or failure in the garden. If you have seen the growth that can be achieved particularly in Taranaki soils or Westmere loam, then you will agree with this statement.
There are several mulches available that will best suit particular plants and soil types. At the garden centre we have bulk landscape supplies of these and other products, and it has been an interesting exercise to source and develop products suitable to specific plant types and categories.
Some of the options available for mulching are poultry compost, Tui Mulch & Feed, mushroom compost, peat moss and pea straw.
One of the heat-loving plants of summer is hibiscus.
Hibiscus is amongst the most favoured shrubs for tropical, subtropical or warm-temperate gardens. In Whanganui, some grow more vigorously and bloom better than others. In selecting hibiscus keep an eye on nearby gardens for robust, free-flowering plants to give you an idea of good plants for your situation. Hibiscus, if regularly fed and watered, responds with healthy growth and displays of superior flowers. They have a strong appetite and need to build energy reserves for constant flower production. An annual feed with Novatec Fertiliser is recommended.
Some early references claim the geographical origin of Hibiscus rosa-sinensis, which literally means "rose of China". Various forms eventually found their way to England. Others suggest it hailed from India. Captain James Cook and other Pacific explorers later found a double red form being cultivated in several island groups. Early botanists suggest Polynesian migrants may have brought hibiscus with them from South-East Asia and then to Hawaii, Tahiti and Fiji.
Earlier crossing of Chinese and native Hawaiian species has resulted in the development of most of the thousands of hybrids grown today. There is much diversity of form, colour and sheer beauty in hibiscus flowers.
If you enjoy hibiscus, I encourage you to find space for one more. If you are just beginning and have yet to experience the delight of picking a hibiscus bloom from your garden, consider giving one of these a go.
Hibiscus grow best in maximum sunlight. They will grow in the shade but need full sun for optimum flower production. If you can, avoid placing them with other plants that compete for available root space and nutrients.
Growing hibiscus in containers is an ideal way of enjoying this beautiful plant at close range. In reasonable conditions, they will thrive on sunny patios, balconies, by swimming pools etc.
Pots are best, with a minimum size of 50cm diameter. Use a good-quality potting mix with a long-term slow-release fertiliser incorporated. Select lower-growing varieties such as the hibiscus longiflora range, as they generally take longer to overcrowd their container. Re-potting is generally necessary after two years. Appropriate feeding, pruning and pest control are desirable. Regular watering is essential and a fitted irrigation micro-tube with adjustable micro-spray or dripper fitting makes this easy to manage.
Annual pruning of hibiscus is encouraged for healthy growth, good flower production and neat compact plants. When the season begins to warm up in the spring, remove about one-third of the previous season's growth. Use sharp secateurs and make an angled cut above the outward pointing bud. Completely remove crossed or wayward branches or any that overcrowd the centre of the bush. Trim off branches within 30cm of the ground to create clearance for mulching, fertilising etc. Bushes soon grow into vigorous new stems.
There are a few different hibiscus types that are available to home gardeners, including Fijian, Clarks Hybrids, Hawaiian, Syriacus and Longiflora.
Hibiscus longiflora is my pick of the hibiscus types. This type produces many more flower blooms than other varieties. Top-quality breeding has resulted in flowers that are produced in profusion at cooler temperatures, starting blooming earlier in the season and continuing for a longer period. To add to the flower power, the blooms of longiflora varieties typically last three to four days as opposed to one day, which has been the norm for hibiscus. The longiflora varieties have a compact growth habit about 80cm to 1.2m high by 80cm wide.
• Gareth Carter is general manager of Springvale Garden Centre