Propagating native plants: Seeds or cuttings?

Newsletter March 2006This article is extracted from Yuruga Newsletter
Vol 14 No 1 (March 2006)

Here at Yuruga Nursery we propagate all the plants that we sell, right here on our own premises. We do this in our Production Section, which is ‘down the back’ since, as a NIASA accredited nursery, it is important that we keep this area protected against the inadvertent introduction of pests and diseases into our production systems.

We propagate our plants from both seeds and cuttings, and occasionally we hear claims that one method is better than or superior to the other. Of course, like everything in life, it’s not as simple as that! So here are the facts of the matter …

Seed propagation

Plants grown from seed are like puppies in a litter, or children in a family – they are all similar to their parents and to each other, but each one is just a bit different to all the others. So just like puppies in a litter, there are big ones and small ones, strong vigorous ones, weak ones and runts.
An important feature of growing plants from seed is natural variation. Seedlings exhibit genetic variation to a greater or lesser degree.

Cutting propagation

Cutting-grown plants are produced by taking small pieces of the stem of a single parent plant and inducing them to grow roots. Because there is only one parent, the new plants are identical to the original parent and to each other in every way. So if the parent plant is tall and straight, the cutting-grown progeny will be tall and straight. If the parent plant has flowers which are large and bright red, so too will the progeny.

An important feature of growing plants by cuttings is uniformity. Cutting grown plants are identical.

At Yuruga, we use both methods (seeds and cuttings), depending on the particular plant and the purpose for which we are growing it.

Ornamental plant varieties

In the ornamental plant world, keen gardeners and nurserymen are constantly breeding new and better varieties – bigger flowers, brighter foliage, hardier drought resistant varieties, dwarf versions for ever-diminishing backyards and patios, etc etc.

Once a special new plant has been developed, it must be propagated from cuttings so that the progeny are true to form, that is, identical to the original plant and to each other. If it was to be propagated from seed, there would be variation amongst the progeny and the specially selected traits could not be guaranteed. Therefore, cultivars, hybrids and special varieties MUST be propagated by cuttings.
So, old familiar favourite varieties such as Callistemon Captain Cook, Grevillea Honey Gem, Melaleuca Revolution Green are all propagated by cuttings, as are new varieties on the market such as Syzygium Northern Lights, Pathfinder and Cascade. If you have bought a seed-grown Callistemon Captain Cook then you have been sold a ‘lemon’, and it could grow up to be pretty well any size and shape depending on what other callistemons were in flower around about at the time to pollinate it.

Revegetation

In the world of revegetation and environmental plantings, on the other hand, it is important to maintain genetic diversity so as to reflect the genetic structure of the natural forest. In this case, seed propagation is the method of choice.

An important part of our business at Yuruga is the supply of plants for revegetation projects, and for creating buffer zones, wildlife corridors, screens, windbreaks and landscapes on properties abutting and adjoining State Forests, National Parks and World Heritage areas. In these highly sensitive areas, the genetic integrity of the plants we supply is very important, and the plants are grown from seed of the appropriate provenance.

Where plants are grown from seed, and the seed source is very limited, there is a danger that in-breeding may impact on the genetic quality of the seedlings. In-breeding is well understood in the animal world, where every farmer knows that herds of cattle become inbred unless a new bull is introduced from time to time. The same applies in plants, and so it is most important that there is continuing access to wild seed from native forests in order to keep our cultivated populations re-invigorated and genetically healthy.

Seed collection from native forests and crown land in Queensland is heavily regulated under the Nature Conservation Act so as to protect our native species in the wild, and an array of permits is required. At Yuruga we have all the appropriate permits, and we liaise closely, and value our relationship with, the EPA and Forestry Departments.

Forestry and other commercial uses

When growing plants for forestry and other commercial uses, plantation yield and profitability are important considerations, and so the careful selection of the best trees is a basic tool in successful plantation establishment. Ideally, cutting propagation of superior individuals is used, but this is not always practical. This may be because it is difficult to produce sufficient plants by this method (striking cuttings is not always easy, and some species are notoriously difficult), or because there has not been any breeding to produce superior plants worth replicating. In this case, propagation is by seed, but rigorous culling of the runts and weaker individuals should be done so as to ensure that only the most vigorous plants are planted in the plantation.

In north Queensland, unfortunately, there are a number of high profile examples of the folly of planting a seed-grown timber plot where no culling was done at the seedling stage. These plots should serve as a constant reminder of the importance of using only carefully selected seedlings in the establishment of a commercial enterprise.

Gardens, screens, windbreaks and general plantings

Provided a particular plant is not a selected variety (in which case it must be grown from cuttings), then plants used for general purposes can be grown from seeds or cuttings. Here at Yuruga we use both methods. If seed is plentiful and of good quality, we use seed. If seed is in short supply or of poor quality, then cuttings are a good alternative. When it comes to seed, it always seem to be feast or famine, so some years we will grow a particular species from seed, and other years from cuttings.

Plants grown from seed are no better or worse than plants grown from cuttings, in terms of the physical structure of the plants themselves, provided the seedling runts have been culled out as discussed above.

Sometimes people will say that the root systems of seedlings are superior to the root systems of cuttings, but this is not true. Seedlings generally have tap roots when juvenile, but in most cases lose the tap root as the plant matures. Cutting grown plants tend to have mature root systems from the start. The root system of a plant once planted in the ground depends on the soil type, ground preparation, and the growth habit of the particular plant itself, NOT on whether it was grown from seed or cutting.

There is no difference in life span between cutting-grown and seed-grown plants, and no difference in growth habit. The timber industry world wide relies on cutting-propagation for timber plantations!