LEARN TO BE AN EFFECTIVE AND PRACTICAL PLANT PROPAGATOR
GET USEFUL: BECOME A SKILLED AND KNOWLEDGEABLE PLANT PROPAGATOR
Good Propagators are one of the most valued staff members in any production nursery. Their speed and strike rate will determine the profitability of the entire nursery. Because of their pivotal role; good propagators tend to always be in demand in the nursery industry, and their job security is high.
To be a good propagator, you need to know how to identify a wide range of plants; and be able to understand and make judgements about what parts of the plant to use and what techniques to apply in order to propagate them effectively. These things are taught strongly in this course.
An effective propagator also needs to be naturally fast and agile in the way they use their hands. These "motor skills" come easily to some people; and far less easily to others. If your fine motor skills are not fast and good, you may reconsider whether a career as a propagator is right for you. If you are great with your hands though and lover working with plants, this could be a dream occupation.
This highly relevant course is based on four core modules which focus on propagation, seed propagation, cutting propagation and horticulture, student may then choose 2 electives to build upon this knowledge further.
Note that each module in the Qualification - Certificate in Propagation is a short course in its own right, and may be studied separately.
You Will Never Stop Learning
As you progress through this course, you will realize that there are thousands of different plants which are being propagated, grown on and sold all the time; and that the techniques used to propagate each of those plants is different.
- Sometimes the differences are subtle
- Sometimes the differences are great
As your knowledge, understanding and awareness of plant propagation develops you will correspondingly develop an ability to make appropriate decisions about the better ways to try and propagate different plant species and cultivars.
It is often quite possible to use a number of different techniques to propagate the same plant, but choices need to be made. One technique may be faster and cheaper to carry out, but may not give the results you need. Another might give better results but be too costly to be commercially viable. Making choices about how to propagate is always a matter of being aware of the possibilities, the likely outcomes, and for any commercial situation, the ultimate cost.
Consider Citrus Propagation
Propagation of citrus may be achieved in a number of ways and the method chosen will largely be influenced by the grower's needs - whether for the garden, nursery or orchard.
Citrus can be propagated by seed, cuttings (stem or root), suckers, budding, grafting or layering. Citrus grown from seed are often more vigorous and have greater disease resistance but they are less productive and take longer to reach fruiting maturity. For these reasons, in the nursery or orchard they are mostly propagated by 'budding' a preferred variety onto an appropriate rootstock. Budding is a special kind of grafting which involves attaching just one bud (often with a thin sliver of wood with the bark still attached) to the rootstock. The end result is the bottom half of the plant has vigorous, disease-resistant roots and the top bears a different variety that produces the desirable growth and fruiting habit.
Suckers may be easy to grow, but plants started from a sucker off a grafted plant are going to be the variety of the rootstock, rather than the top graft.
Some citrus grow readily from stem cuttings, and others don’t. Some may grow easier from a root cutting than a stem cutting (e.g. the closely related genus, Eremocitrus strikes easier from root cuttings than stem cuttings).
Stem cuttings should be taken of semi ripe wood in summer. Cuttings should be about 7 to 10cm long from just below a bud, and the leaves should be removed from the bottom two thirds of the stem. Place the cuttings in a propagation mix of equal parts peat or coir and washed sand. Cuttings will need to have a steady temperature of 16-18°C, so in cooler climates they may need to go into a cold frame or greenhouse. Once they have established root systems the new plants may be hardened off by slowly exposing them to outside temperatures. They should be ready for planting out in the second spring after propagating.
Layering is a method of propagating from an existing tree by forcing a stem to grow roots whilst still attached to the tree. The obvious disadvantage with layering is that new trees won't have the benefits of those grafted onto good rootstocks. It may be carried out on trees where stems can be made to reach the ground without snapping them. Alternatively, mounds of soil can be built up to flexible stems, or air layering may be used. Whichever method of layering is adopted, a small cut is made to the stem and rooting hormone applied. The wound is then buried beneath soil and pegged into place. With air layering the cut is wrapped in moist material such as sphagnum moss and sealed inside a polythene tube. After a number of months roots should have emerged from the wound and the new plant may be detached from the parent plant.
Seedlings from citrus commonly exhibit “nucellar embryony”. This is where the germinating seedling develops without cross-pollination, and it only exhibits characteristics of the plant which the seed develops on.
When the seed results from cross-pollination, the characteristics of the seedling are going to be relatively unpredictable. When the seeling grows from a seed with only one parent, the characteristics will be the same as its one parent.
Many home gardeners and enthusiasts enjoy growing citrus from seed. Whilst it takes longer to attain fruit bearing plants, if you have the patience it can be worth the effort. Typically citrus grown from seeds take about 10 years to bear fruit. It can be a long wait given that they may not be true to type or could have inferior quality fruits. Nevertheless, a tree produced from a seed will usually become more productive than a grafted one once it reaches its peak. Home gardeners may also use seeds to develop suitable rootstock plants, although this is not wise on a commercial basis.
If seeds are not purchased then they need to be extracted from fruits and thoroughly cleaned. They can either be dried on paper towels and stored in polythene bags in the fridge, or planted straight away. Soaking the seeds overnight in water prior to planting may help break dormancy.
Seeds should be sown in spring in trays or pots of good quality seed raising mix at a depth of 0.5 to 1cm. Alternatively make a mix from equal parts sand or perlite to coir or peat. This can be varied to up to two thirds sand or perlite to one third peat or coir. Place trays where they receive plenty of sunlight and warmth. Keep them moist but not wet. Seedlings usually begin to emerge after 7 to 10 days for a couple of weeks thereafter.
If grown in trays, once seedlings are large enough to handle prick them out. This will be when they are 2 to 5cm tall. Put seedlings in larger pots and continue to grow and re-pot as necessary. Harden off before putting into permanent positions. This may take several years.
Grafting (ot Budding)
A grafted tree may begin to bear fruit after two to three years rather than the six to seven years a seed grown plant takes.
Rootstocks used for grafting onto are chosen because they have advantageous characteristics with respect to:
- Growth vigour - overall hardiness, tolerance of poorer soil conditions and speed of growth.
- Fruit size - improved quality due to optimal size for best taste.
- Time to harvest - the cropping season can be made to start earlier and last longer.
- Pest and disease resistance - e.g. from phytopthera root rot, citrus nematodes.
- Dwarfing habit - this prevents the top from growing too big and thereby makes harvesting easier.
- Cold tolerance - can withstand lower temperatures than they would ordinarily.
- Adaptability to different soil types - e.g. sandy soil, heavy clay, saline soils, alkaline soils.
Very often, rootstocks combine a number of these different advantages e.g. cold tolerance, vigorous growth and dwarfing habit. Aside from ease of harvest, a dwarf habit may be beneficial because it gives rise to bushy growth so that less pruning is required to maintain shape.
Rootstocks have to be chosen carefully. Not all rootstocks are compatible with all varieties of citrus. For example, the Eureka lemon is incompatible with Poncirus trifoliata rootstock. There are many other unsuitable combinations.
Also, the choice of rootstock will be affected by the growing conditions. For example if the soil has a high concentration of citrus nematodes then a rootstock with better resistance will be needed. It should be noted that a rootstock may have resistance to some diseases but not others. For example, Poncirus trifoliata has excellent resistance to the citrus nematode, phytopthera and tristeza but poor resistance to exocortis. If exocortis is present then other rootstocks with better resistance should be considered.
If the soil has poor drainage or is highly saline or alkaline, again these factors will affect the choice of rootstock. For instance, Benton citrange rootstock is adaptable to sandy soils, loam soils, and soils with poor drainage but it is not a good choice for alkaline or saline soils. Whether the soil has previously been used to grow citrus will also have an effect on rootstock suitability.
For commercial growers choosing the right rootstock can affect fruit quality. Fruit quality can be measured in a number of ways including size, thickness of rind, texture of rind, fruit acid content, fruit juice content and even the total soluble solids.
The rootstock can not only influence fruit size and quality, but also the time to harvest. Timing can make a huge difference in terms of profitability. If your fruits come onto the market when it is already flooded the price you can command will be less. If they become available later in the season, there may not be as much demand.
Budding is done onto stems at about 12-15cm above ground level. It is usually undertaken when the stems are about 5-8mm in diameter. The stem to be grafted onto should be cleared of any thorns and shoots. The budding material is taken from buds just behind the current growth flush or from the current growth flush where it has started to harden off. It is preferable that it is from stems about the same diameter as the rootstock. The bud wood should always be taken from healthy specimens.
After cutting the bud wood from the selected plant any parts not needed should be cut off. The bud wood should be in 20-25cm lengths. Leaves must be removed leaving a petiole of about 2-3mm to protect the bud. The bud wood should either be used at once or stored refrigerated in plastic bags for up to three months.
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