There are not too many trees and shrubs that choose summer for their main flowering period. It makes sense, in that there is likely to be a shortage of water and thence food, in the hotter months so it is better to get flowering over and done with early in the spring season, then concentrate on building up reserves for the colder season ahead.
Fortunately, there are exceptions to the rule, and some plants reserve their best displays for summer.
One that always seems to do well in the Wairarapa heat is the slightly unfashionable Nerium, or oleander – whose botanical name is Nerium oleander! The oleander bit of the name is said to be a reference to the similarity of the plant’s leaves to those of an olive [botanically an Olea], but it is an ancient name and its origin is probably a little contentious.
It has been grown in gardens for millennia – it was certainly grown by the ancient Greeks, no doubt brought into cultivation from the wild where it occurs from North Africa, through the Mediterranean and across Asia to China. It grows in dry places and can withstand considerable drought.
Needless to say, it is now grown in warm areas all around the world, including Galveston in Texas. It is so prolific there that Galveston is known as ‘Oleander City’ and hosts an annual oleander festival. It is also the official flower of Hiroshima, being the first tree to flower after the World War II bombing.
In New Zealand, it can be found in many older gardens but seems to have fallen slightly out of fashion. It may be because of the supposed extreme toxicity of the foliage, but the danger is probably overstated.
The leaves and branches do have toxic compounds, but both are extremely bitter, and people are unlikely to consume them. However, some animals are sensitive to the leaves, and horses have been struck after eating them.
There is an urban legend about a scout troop who skewered sausages on oleander branches, cooked them over a campfire, then all died. It is untrue and has been circulating for more than a century.
Obviously, no one suggests using the branches for that purpose, and you should be careful when handling the plant as it can cause skin irritations, and eye inflammation if you are incautious.
Having said all that, these are among the prettiest of summer plants. I am especially fond of the fully double salmon-orange form called “Mrs F Roeding’. It seems to almost have a hint of lilac in the flowers as they age, and the effects of a plant in full flower are breathtaking.
There is an older variety called ‘Punctatum’, which has bright pale pink flowers. This is one of the most floriferous of all forms, and often flowers through from late spring to late summer. It makes a wonderful informal hedge in dry, sandy areas.
I find the white-flowered forms tend to be a little shyer of flowering, but have some of the prettiest bunches. One of the best is ‘Madonna Grandiflora’ with pure shining white hose-in-hose flowers – one flower sitting atop the other. It appears to flower later than some of the other forms, and it is looking very nice now.
Oleanders are plants for warm and dry places – they will sulk if planted in too much shade, and they are not keen on wet feet either. In damp conditions some varieties are prone to botrytis attacks on the flower buds. They develop a grey mould and drop off the plant. The deeper-coloured forms seem more prone, but it has not been a problem this year with the drier weather.
Another plant that waits for later in the summer to kick into flowering is the blue-flowered South African shrub that is named after lead – Plumbago capensis.
This is a plant that cannot make up its mind about whether it is a shrub or a climber, and sort of ends up being neither – a lax growing plant that will flop around and over anything it can find. The foliage is a nice dark green, held on slender stems. The heads of flower are usually light blue, but there are white and deeper blue forms around, and other species [not grown in New Zealand as far as I know] even have red flowers.
This is another plant for dry areas – we have a bush popping out from under evergreen trees, and it copes with that, although it always sends its arching branches out towards the light before flowering.
There is another flower with faint blue flowers – the odd little tweedia, Oxypetalum caerulea. This is another clambering plant, usually grown as an annual although it is a frost tender perennial, with the added attraction of supposedly being a substitute feed source for Monarch butterflies.