Notes on Growing Welwitschia mirabilis (Hook.E) From Seed
By Ed Perfect, Kitchener, Ontario
Welwitschia mirabilis is a unique, tap-rooted plant from the Namib desert in the south-west of Africa. Because of its rarity and tap-rooted (non-clustering) nature, the only practical method of propagation is by seed. I have about ten years experience in growing this plant from seed. Some notes on my successes and failures are given below.
Seeds: The seed has a high oil content which turns rancid over time resulting in loss of viability. To maintain viability, seeds should be stored in a frozen state in a freezer. Germination is improved if seeds are dewinged and denuded of their outer seed coats. The seed is thought to contain a chemical germination inhibitor (visible as a yellow stain on blotting paper used to sprout unsoaked seeds). Therefore, it is advisable to leach this chemical out of the seeds by soaking them overnight before sowing.
Sowing: Welwitschia is particularly susceptible to damping-off. Thus, always add a little fungicide such as Captan or Chinosol to the water. The seeds can be sprouted on moist blotting paper and then potted up, or placed directly (flat) on the soil surface and covered with a small pile (1/8′-I/4″ high) of coarse sand or brick chips (to prevent the taproot from thrusting the seedling out of the soil).
Soil: Use a pasteurized soil mix or sterile ‘soiless’ media. In the past I have used the following soil mix: 1/3 gritty sand, 1/3 perlite, 1/6 peat, 1/6 loam. Currently I am experimenting with the use of soiless media containing composted bark to improve root development and cut down on fungal infections.
Containers: No need to use a drainpipe to accommodate the long tap root as once was thought necessary. Simply use a regular 4″ clay pot (one seedling per pot), which is big enough for the first 5 years of growth. The tap root will grow around the bottom of the pot; this practice is similar to the bonsai method used with trees, except no pruning is done.
Germination: In a propagator with bottom heat, germination usually takes place within 5 to 15 days. As soon as both seed leaves (cotyledons) are fully emerged, the seedlings should be removed from the propagator. The seedlings are light red at first and turn green as they produce chlorophyll in good light. Germination tends to be variable depending on the age and source of the seeds. Some batches give germination rates of 70% or more while others give less than 10% success rate.
Cultivation: The seedlings should be grown in a warm greenhouse or under artificial lights. They will
respond well to frequent waterings, mistings and dilute fertilizer applications during the growing season. Poor drainage and standing water should be avoided. Never expose the young plants to prolonged drought, even during periods of dormancy. Plants are most sensitive to fungal infection and drought stress during their first 18 months of life. After this time the plants become much more resistant. About one month after germination, the two true leaves start to emerge from the crown opposite to the cotyledons. These grow from the base of the crown and die back at the tips. The cotyledons dry up and abscise after approximately 2 years.
Transplanting: Welwitschias dislike being transplanted at all stages in their lives. Because of the sensitivity of the seedling to fungal infections and drought stress, reporting should be delayed until the plants are approximately 5 years old. Seeds should be sown individually in pots of sufficient size that they can remain in them for a number of years. The same practice should be followed when potting up so as to reduce the amount of disturbance to the taproot to an absolute minimum. Extreme care must be taken not to break the tap root and the soil should not be allowed to dry out after transplanting. A systemic fungicide can be applied to help prevent infection of any broken fine roots.
Sources: The availability of field-collected seed is highly variable because of periodic beetle infestations. In good years the following people occasionally have seed available: Doug and Vivi Rowland, 200 Spring Road, Bedford MK42 8ND, England; Sue Haffner, CSSA Seed Depot, 3015 Timmy, Clovis, CA 93612-4849, USA. In addition, the ISI program of the Huntington Botanical Gardens, 1151 Oxford Road, San Marino, CA 91108, USA sometimes offers seed harvested from plants in their collection.
(This article was originally published in The Amateurs’ Digest 1995 Special Edition)