Tuberous drosera

Introduction

Tuberous drosera are a type of drosera or sundew that form a tuber at some stage in their life cycle.Usually this is an annual event and corresponds with a time of dryness or harsh growing conditions.For example most tuberous drosera are found in southern Western Australia which has a climate with cool,wet winters and hot,dry summers.With the Western Australian species the tuber is produced in summer,the plant dies off above ground and survives the summer underground.In Autumn when the rains resume,shoots form and the plant begins growth above ground again.By next spring or early summer the plant is full size and usually flowers.The plant then dies back and the cycle begins again.There are exceptions to this rule however with some species not going dormant until well into summer due to growing in wetter habitats.Some other species growing in dryer habitats go dormant in spring.In Eastern Australia some tuberous drosera growing at high altitude actually are dormant in winter which is the harshest season for them with temperatures too low for active growth.In summer there is plenty of moisture around and warmth so the high altitude tuberous drosera are in active growth then which is the complete opposite to most tuberous drosera.Drosera lunata from North Queensland survives in tropical conditions and is in active growth in summer which is also the wet season.In winter which is the dry season it produces a tuber and survives underground.

Distribution

There are approximately 60 species most of which grow in the South West corner of Western Australia. There are several types growing outside of Western Australia.These are Drosera aberrans,Drosera schmutzii,Drosera whittakeri,Drosera praefolia,Drosera macrantha,Drosera peltata,Drosera hookeri,Drosera auriculata and Drosera lunata. Drosera lunata is the only species that grows outside of Australia and New Zealand and extends into south east Asia and possibly beyond.

Drosera aberrans.A rosetted tuberous drosera.

Drosera tubaestylus tuber with decaying stolon.

Drosera macrantha tuber resuming growth in Autumn.

Types

There are a few different types of tuberous drosera including the rosetted types which have large leaves (up to 5cm across although usually smaller)and form a ground hugging rosette.The stemmed varieties that usually have a long stem which may sometimes be climbing and can reach heights of 2m or more above the ground although most types are in the order of 20cm tall.These types usually have small leaves (approximately 1cm across) as most of their energy goes into producing the stem.The stem forming types have evolved to grow in habitats with other plants so must invest some energy to get the leaves high above the ground otherwise they won't get enough light to survive.Most types of tuberous drosera,just like pygmy drosera which often grow in the same habitat,have flowers which are 5 petalled,short lived and close at night.Flowering usually occurs toward the end of the growing season although there are some notable exceptions such as Drosera zonaria which produces flowers before foliage.

Drosera hookeri.An erect stem forming tuberous drosera.

Drosera hookeri in central Victoria in spring(16-10-2005) just before flowering.

Drosera modesta ,a climbing stem forming tuberous drosera

Drosera erythroriza ssp collina

Cultivation

If you are lucky enough to live in a climate similar to Perth,Australia or Melbourne, Australia which is a climate suitable for most tuberous drosera, cultivation is actually fairly simple and rewarding.You can leave the plants outside in the rains over winter with the occasional extra watering and keep them under cover when they go dormant in summer. If you live in an alpine area or similar you might want to give the high altitude Drosera peltata from Eastern Australia a go. In the tropics it is recommended that you grow Drosera lunata. Elsewhere you need to take a lot more care to grow them well.

The following instructions are for the temperate tuberous drosera, other types will be similar

POTS - Ranging from 4 inch to 12 inch or more depending on the species. The larger the tuber the bigger the pot needs to be. As a rough guide you can multiply the size of the tuber by 12 to get the required pot height.

LIGHT - Light shade in late spring to early autumn to full winter sun. Different species prefer different amounts of sun. Even different varieties of the same species prefer different amounts of sun. It is sometimes a matter of experimentation as to what works best. Please note that full summer sun is usually too strong for them and if you expose them to it at the wrong time they will probably die or form a very small tuber.

WATER - Water from the top of the pot every day or two or sit them in a shallow tray of water during the growing period, allowing the water to dry out for a couple of days before refilling. Never allow the pots containing tuberous drosera to sit in water continuously as this can rot their tubers. As with most things mentioned here there are a small number of exceptions.

COMPOST - most types grow well in 2 parts peat to 1 part washed sand. Some varieties need more sand such as Drosera zonaria and some Drosera erythroriza varieties.

HUMIDITY - moderate

PHOTOPERIOD - 10 hours in winter. 14 hours in summer.

TEMPERATURE see Perth,Australia. While most species handle winter nights down to 0 degC well, most do best with some protection from frost.

PROPAGATION - Many species produce extra tubers when they go dormant, simply seperate and pot these up next season. Some clones produce extra tubers nearly every season while other clones rarely do so. Fortunately there are other ways to get extra tubers such as leaf cuttings. These work for most tuberous drosera and are done as standard drosera leaf cuttings. Sometimes under conditions of high humidity tubers will form from leaves that are still attached to the main plant.Seed also works well with a large number of species self pollinating. It is probably best if you let the seed get hot in the summer before they are sown in autumn.

Drosera stolonifera tuber clump.

Drosera gigantea tubers forming from leaves.

SPECIAL CARE - Tuberous drosera have a dry, summer dormancy period. Once they go dormant (die off above ground) you should keep them away from any water. However a minority of species, such as D. whittakreri and D. aberrans like to be kept slightly damp over that period. Most species will tolerate a small amount of moisture over summer without problems. In Autumn, when new shoots start growing, watering should start again gradually. During spring and autumn it is important not to let the sides of the pot get too hot from the sun otherwise the plant may be harmed. Light shading or surrounding the pot with nearby plants to protect it from direct light helps to prevent this.