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DeutschOnce the seeds are up, you need to select your rootstocks: weed out off-type or poorly rooted plants, then train a single, straight stem. Here is how I go about it, from emergence to a plant ready to graft.
At a glance
- Who it is for : growers who have sown their own rootstocks (see raising rootstocks from seed).
- Timing : first sort after 6 months; selection when potting on, after a year; grafting in the second spring.
- What I keep : the best plants, about 20% of the seedlings: at least 15 cm after a year, with a nice straight root.
- Potting on : into 11x11x20 pots.
- Ready to graft : in the second spring, or a year later for slower varieties such as Poncirus.
On this page : Why select · Polyembryony · Plants to discard · Selection step by step · When to graft · Common mistakes
Why select the plants?
Especially if the seed is not certified: the flowers may have been pollinated by any citrus pollen in the area.
It is then best to make a ruthless selection of the rootstocks, to guarantee their characteristics (hardiness, suitability for the soil, fruit quality, productivity, early bearing…). Otherwise it is a lottery, and home growers rarely have the time or space to play :)
Polyembryony, nucellar, zygotic: what does it mean?
Polyembryony simply means that one seed can contain several embryos. By taking sections of the ovary, researchers observed that these embryos do not all have the same origin:
- zygotic embryos come from the fusion of a male and a female gamete (sexual reproduction): the seedlings may therefore be hybrids if the gametes were genetically different;
- nucellar embryos arise from budding of the nucellus (maternal tissue), without fertilisation: they are genetically identical to the mother plant.
In theory, nucellar seedlings are identical to the mother plant; yet new varieties have been created by grafting a bud of nucellar origin onto a rootstock to compare it with the mother plant (Silverhill satsuma, for example, comes from a nucellar seedling of Owari).
Several seedlings per pip
A pip may contain 10 embryos, or even more depending on the variety. But only embryos larger than 5 mm will germinate and have enough reserves to get beyond the stage of a small root.
Polyembryony: three seedlings remain on these one-year-old plants.
The largest embryo is often nucellar (H. J. Webber), but not always! Without going into detail, gamospermic polyembryony produces two identical, vigorous zygotic seedlings; this happens in fewer than 1% of cases, and a home grower has no way of telling.
Moreover, since only embryos larger than 5 mm produce a seedling, a single seedling is not necessarily nucellar. Likewise, when two seedlings appear, the larger may be the zygotic one if it germinated first, but statistically that is not the most common case.
To keep it simple
It is best to use certified seed and to keep the most developed plants as rootstocks: statistically, they stand a good chance of being identical to the mother plant.
Which plants to discard?
1Plants unlike the mother plant (from 6 months)
After 6 months you can start sorting out those that are phenotypically different: for example bifoliate leaves from a trifoliate mother plant, which often happens with C35.
A bifoliate leaf: a plant to discard.
2Albino plants
At emergence you may see a few albino plants: they will die on their own, for lack of photosynthesis.
An albino seedling.
3Faulty roots (when potting on, after a year)
After a year of growing, when potting on, discard every plant with root problems. In these photos I removed the compost so it shows clearly, but I prefer not to bare-root plants, because they take longer to re-establish.
Root defects (red arrows).
4Keep the straight roots
Keep only the finest plants, those with a nice straight root.
A straight root: a plant to keep.
5Gooseneck roots
A professional, fine-grade compost prevents this defect, known as a gooseneck.
Gooseneck roots (red arrows).
6Checking without unpotting
To check a plant without bare-rooting it, simply scrape away the top 2 cm of compost (easier with a professional compost): root defects are often found there, caused by a germination problem.
The collar exposed by scraping the compost.
Selecting and training the rootstock
1Mark the polyembryonic seedlings
Where there is polyembryony, mark all the polyembryonic plants with a toothpick or a label.
Marking pips that produced several seedlings.
2Cut out the weakest
After a year, when potting on, cut out the weakest seedling, if it has not died already.
At potting on, only the strongest is kept.
3Keep plants of at least 15 cm
After a year I keep the finest plants: they should be at least 15 cm tall. If not, conditions were not ideal (temperature, container depth, compost, fertiliser…).
At least 15 cm after a year.
4Benchmark: the finest plants
The way I grow them, the best 10% here reach about 50 cm including the root after a year, and the citrumelos are 4 to 5 mm in diameter.
About 50 cm, root included, after a year.
5Pot on the best
After a year of growth, in spring, I keep only the finest plants (20% of the seedlings) and pot them on into 11x11x20 pots.
The best, potted on into 11x11x20 pots.
6Re-form the leader
When growth resumes, I remove all shoots except the 3 highest, to re-form the leader.
The 3 highest shoots (red arrows).
7Keep a single shoot
A week or two later, I keep only the shoot that is the most vigorous and best aligned with the stem.
Keep the best-aligned shoot.
8The plant is ready to grow
Over the year, make sure the plant grows straight and remove young side shoots, to get a single, straight stem.
The plant, ready to grow.
When to graft?
In the second spring, the plant is ready to graft! You can wait another year for slower-growing varieties such as Poncirus, to get thicker rootstocks, or simply if you have no scion wood.
For grafting: cleft grafting · whip-and-tongue grafting · bark grafting · chip budding.
Common mistakes and how to avoid them
Keeping every plant from uncertified seed
Select ruthlessly: the flowers may have been pollinated by any citrus nearby.
Assuming a single seedling must be nucellar
It is not certain: keep the most developed plants, which statistically stand the best chance of being true to type.
Keeping plants unlike the mother plant
Discard them from 6 months (for example bifoliate leaves from a trifoliate mother plant).
Bare-rooting plants to check them
Scrape away the top 2 cm of compost instead: the plant will re-establish faster.
Coarse compost
A professional, fine-grade compost prevents gooseneck roots.
Leaving several shoots at the top
Keep the 3 highest when growth resumes, then just one, the most vigorous and best aligned.
Grafting a rootstock that is too thin too early
Wait another year if necessary, especially for Poncirus.
Going further
- Raising rootstocks from seed : choosing the seed, container and compost, sowing step by step.
- Certified rootstock seed : to limit off-type plants.
- Plant-in identification labels for rootstocks
- How to choose a rootstock : to pick the right rootstock for your area.
- Rootstocks : the nursery's rootstocks.
No time to sow and select?
The nursery also offers rootstocks. A question about your seedlings? Get in touch.