Alstroemeria, Peruvian Lily, Lily of the Incas

In the past these beautiful plants have always been difficult to raise from seed. Julia Kerley describes how she went about finding a reliable method and describes a simple technique.

Alstroemerias were named in honour of an 18th century Baron, Clas Alstroemer, who was a friend of Linnaeus (father of modern plant naming), they are a genus of about 50 species of South American tuberous rooted perennials. Although often known as Peruvian Lilies, in fact most species originate from Chile and only a few are hardy enough to live outdoors in Britain.

Among these hardy species is A. ligtu from which the exceptionally elegant 'Ligtu Hybrids' are derived. They grow from 2½-3ft. (75-90cm) tall bearing masses of exquisitely marked six-petalled flowers in a rainbow of colours ranging from shell pink, peach and apricot through to white, yellow, and vivid flame. The flowers which each measure about 2in. (5cm) across, are carried in huge clusters on stout but fleshy stems. They have an extremely long vase life which, coupled with their unique and outstandingly beautiful appearance, makes them equally beloved of gardeners and flower arrangers alike.

Although the 'Ligtu Hybrids' are so charming and such desirable garden plants I have long recognised that seed is difficult for the gardener to germinate unless sown as soon as it has been shed from the mother plant. Seed obtained from seedsmen, even when it is sown under the precise conditions recommended by gardening experts, usually gives only a few seedlings; even those which do appear can take anything up to 12 months to come through.

Apparently this reluctance to germinate is caused by mother nature devising a safety mechanism to ensure survival of the species in the wild. And what happens is this: if conditions are not right for germination and establishment to take place as soon as the seed is shed from the plant, it becomes affected by dormancy. This is a resting stage which further delays germination until soil and weather conditions are suitable for that seed to start into growth, and for the young seedlings to become established. In this way the chances that the plant will perpetuate itself successfully are enhanced.

Now, although delay mechanisms may help survival in the plants' natural habitat, they can be unbelievably frustrating for the gardener who has 'planned his patch' and is eagerly awaiting a fine display of flowers.

In laboratories we have spent several years researching the effects of environmental conditions on seed germination. The breaking of Alstroemeria dormancy was a challenge. My goal was to find a simple cultural method which would give rapid and complete germination of 'Ligtu Hybrids' so that gardeners could discover the pleasures of growing them. Experience and a sixth sense indicated some possible directions to proceed in.

First steps

Before doing anything else I checked that the seeds were viable. I decided to conduct a rapid biochemical test on a small number of seeds from a batch of A. ligtu. Seeds were soaked in a colourless solution of the chemical Tetrazolium. In this test, seeds take up the chemical, which reacts with the processes being carried on within living cells to form a noticeable stain. This makes it possible to distinguish the red-coloured living parts of seeds from the colourless dead ones and so determine the percentage of viable seeds. The results of my staining test showed that 90% of the seeds were viable and had the potential to germinate.

Armed with this finding I progressed to the second step of my research to find out what type of dormancy the seeds possessed. I could then find the right conditions for actually breaking the dormancy.

I had noticed when soaking the seeds that they took up moisture very readily. So I was able to conclude that dormancy was not being caused by impermeable seed coats (which prevent the uptake of moisture and oxygen). There was every indication that the germination restraint was internal.

To overcome internal dormancy of the seed embryo there are two methods commonly used. In both cases the seeds are sown, then subjected to pre-treatment, before being placed in warmth for germination. The difference between the two methods lies in the nature of the pre-treatment. In one it consists of a period of cold stratification whereas in the other it consists of a period of warmth followed by a period of stratification. Stratification involves the exposure of sown dormant seeds to a cold or warm treatment which induces germination.

I had no pointers to which of these methods might prove successful, so I decided to set up an experiment testing out the potential of both. Four lots of 50 seeds were sown for each temperature programme. As a control, a further four lots of 50 seeds were placed in moderate warmth to stimulate the standard method adopted by most gardeners.

The three treatments were:

• Sowing 1 - chilled in the refrigerator at 40F (5C) for 4 weeks then transferred to 60F (15C).
• Sowing 2 - placed at 60F (15C) for 2 weeks then transferred to the refrigerator at 40F (5C). Removed after a chill period of 2 weeks and placed at 50F (15C).
• Sowing 3 (Control) - placed at 60F (15C).

The experiment was examined daily in order to record exact details of germination times and subsequent development of the seedlings. After a period of 12 weeks I noticed a number of white specks, tiny root tips, starting to emerge in Sowing 2. Happily within the space of a further 10 days 60% of the seedlings had germinated. From then on germination took place slowly and sporadically. The final outcome was that 72% of the seedlings germinated in 12 months.

Strangely, Sowings 1 and 3 behaved very similarly to each other - only a few seedlings germinated over the 12 month period.

The experiment showed that although a combination of warm and cold stratification (as used in Sowing 2) gave much quicker and more even germination results than the other methods tested, completely rapid and total germination had not been obtained. Only 72% of the seedlings had germinated (and of those, 60% readily) whereas my quick viability test indicated that 90% of the seeds were capable of germinating. Clearly I needed to refine the duration and temperatures of the pre-treatments in this double stratification technique.

This stage was comparatively simple. I set up a number of sowings using slight variations in times and temperatures of the warm and cold stratification periods. For a control I used a repeat of the method which had proved partially successful in the previous experiment. In one test, complete and rapid germination was obtained.

Now the final stage was to check that this new technique would be effective for conventional sowings in seed compost and for different batches of seed produced in varying climatic conditions. To my pleasure, all was well. In each case the temperature regimes which had proved so successful in the laboratory experiments were equally successful for all sowings in compost. From now on raising the beautiful Alstroemeria 'Ligtu Hybrids' would be within the scope of all gardeners.