The Saguaro cactus is one of the most recognisable of all cacti, as its distinct shape features in many Western movies. It is native to the state of Sonora in Mexico and areas of California and Arizona in the USA.
Saguaros are very slow growing, often only putting on a couple of centimetres/inches in the first 10 years or so, but they are very long lived – living on average 150-200 years. In that time they can reach heights of 12-18m (40-60ft) in the wild, although this is highly unlikely in the UK – and you’d need a very tall greenhouse or conservatory to keep one that old!
The Saguaro cactus has a smooth, waxy skin and, when mature, is covered with 5cm (2in) long spines. In summer, it bears very attractive creamy-white flowers with yellow centres, measuring up to 7.5cm (3in) across.
Indoors Saguaro cacti need a brightly lit position, preferably a south-facing or west-facing aspect or grown in a conservatory or heated greenhouse with good, all-round light.
They are not cold or frost hardy, but can be moved outside to a warm patio in partial sunlight in summer – plants will burn if placed in full, strong sun for long periods. Make sure you bring them back indoors before the weather turns cold in early autumn. They don’t like temperatures below 15C (60F).
There is only the species, Carnegiea gigantea, and no varieties are available.
Like all other desert cacti, plants need a very well-drained compost, so either add extra grit to a John Innes Compost or, better still, use a compost specifically recommended for cacti and succulents. Make sure not to plant too deeply or cover the stem with compost.
Add a topdressing of gravel or pebbles on top of the compost to produce a natural, finished look and to help prevent the base of the plant sitting in wet compost. This will also help weigh down the pot and help prevent it falling over as the plant grows taller.
Houseplant, indoor plant, summer patio plant.
Being a desert cactus, many people think you don’t have to water them. While they can survive long periods of drought by storing water in their stems, they grow – and flower – much better if given adequate supplies of water. Water moderately when plants are in growth (from March/April to September), but more sparingly when dormant – once or twice a month may be sufficient in autumn and winter, depending on the temperatures plants are grown in. Allow the compost to dry out slightly before watering again.
Feed with a balanced liquid plant feed every 2 to 3 weeks during the growing season from spring to late summer.
Saguaro cacti have a weak root system, so don’t grow them in too big a pot. And don’t repot them until absolutely necessary – possibly just to provide extra bottom weight to stop the plant falling over when it gets too big.