How to Graft a Pomelo Tree? Latest Technical Method Tutorial Explained in Detail

The pomelo is a tree of the genus Citrus in the family Rutaceae, also known as pomelo, buntan, xiangluan, zhuluan, neizi, etc. Seedling propagation is mainly done by grafting. Normally, a pomelo seedling grown from seed takes 5 to 8 years to bear fruit, whereas a grafted seedling will bear pomelos in the same year as long as the mother plant has already fruited; if it suffers freeze damage, it can also bear fruit after a year of recovery. Now let us take a look at pomelo tree grafting and seedling propagation techniques!

Selection of Pomelo Tree Rootstock

1. Sour pomelo: A pomelo tree on sour pomelo rootstock has a well-developed root system, a strong taproot, strong affinity, a high survival rate, vigorous growth, a tall canopy, strong adaptability, high yield in the full-bearing period, and good fruit quality. However, it comes into production relatively late and is susceptible to gummosis.

2. Trifoliate orange: A pomelo tree on trifoliate orange rootstock has fairly good affinity, can dwarf the tree vigor, grows robustly, comes into production and bears fruit early, and has good quality. However, it tends to age prematurely in the later stage, and the yield is low.

Cultivation of Pomelo Tree Rootstock

1. Seed collection: The fruits (sour pomelo or trifoliate orange) used for seed collection of rootstock seedlings are harvested when fully ripe, cut open, and the seeds taken out and rinsed clean, then spread out in a ventilated, shady place and air-dried until the seed coat turns white.

2. Sowing: Seeds sown immediately after collection have a relatively high germination rate. If not sown right away, they can be mixed evenly with 3 to 4 times their volume of clean wet river sand (with a moisture level such that it forms a ball when squeezed in the hand and breaks into a few pieces when spread out), piled indoors in a cool, wind-sheltered place with a pile height of 35 to 45 cm, with a bottom layer of sand about 5 cm thick on two sides, covered on top with plastic film to retain moisture, and the edges pressed down with film to prevent rodent damage.

3. Management: After sowing, press the seedbed surface lightly with a wooden board or similar so that the seeds enter the soil, cover with river sand, burned soil, or fine soil until the seeds are no longer visible, then cover with 3 to 4 cm of rice straw, secure the straw with straw rope, and water thoroughly. After sowing, keep the soil moderately moist. After emergence, remove the rice straw in stages so that the seedlings receive sunlight and to prevent bending. Fertilizer management at the seedling stage should follow the principle of frequent application of thin fertilizer. Before 3 to 4 true leaves appear, watering should be reduced and fertilizing stopped. Seedlings are prone to damping-off, so attention should be paid to controlling damping-off, swallowtail butterflies, leafminers, and other pests and diseases.

4. Transplanting: When the seedlings have 10 to 14 true leaves and are more than 10 cm tall, they can be transplanted. If cultivating new-planted seedlings, transplant in May to June of the same year after sowing. Graft in winter or the following spring; the entire seedling-raising period takes two years. If cultivating old-planted seedlings, transplant in the autumn of the same year after sowing or in April to May of the following year after the spring shoots have matured, graft in the winter of the second year or the spring of the third year; the entire seedling-raising period takes 3 years.

Collection of Pomelo Tree Scions

1. Scion collection: Scions should be collected from robust mother trees that are high-yielding, stable-yielding, of high quality, and free of quarantine pests and diseases, or from young trees directly propagated from these superior mother trees or from seedlings in a scion orchard. Choose autumn shoots or spring shoots from the middle and upper parts of the outer canopy that are plump, have full buds, moderate thickness, and complete, glossy leaves as scions. Scions should be collected on a windless sunny morning after the dew has dried or in the afternoon when sunlight is weaker; rainy days are not suitable. Immediately remove the leaves after cutting the scions.

2. Storage and transport: Grafting survival rate is higher when scions are collected and grafted immediately. If the quantity is large or long-distance transport requires storage, they can be layered with clean wet river sand (with a moisture level such that when a hand is inserted into the sand, sand sticks to the hand but not to the fingernails), and during storage they should be checked frequently, the sand moisture adjusted, and rotten branches and scions removed to prevent spread. In the lower-temperature seasons of winter and spring, they can be stored for 50 to 60 days.

Pomelo Tree Grafting Techniques

1. Single-bud cut grafting method

① Cutting the scion: Place the angular side of the scion facing up and the flat side facing down against the index finger, and make a forward diagonal cut about 1 cm below the bud, with the cut surface at a 45° angle. Then turn the flat side of the scion facing up, and from near the bud cut forward to remove the bark layer, requiring the cut surface to be smooth, just reaching the cambium, and preferably slightly exposing the white part of the xylem. Then turn the scion sideways with the bud facing up. Cut it off about 0.2 cm above the bud and place it in a basin of clean water.

② Cutting the rootstock: At 6 to 8 cm above the ground on the rootstock, choose a smooth side and diagonally cut off the upper part of the rootstock, with the cut surface at a 45° angle. Then below the diagonal surface, make a vertical cut along the junction of the bark and xylem, with the cut surface preferably just showing the white xylem. The length of the cut surface depends on the length of the scion.

③ Inserting the bud and wrapping: Choose a graft bud as close as possible in size and length to the cut surface of the rootstock, insert it into the cut surface of the rootstock so that the base of the bud fits tightly against the bottom of the rootstock cut, and the cambium of the rootstock and the cut surface of the scion are in close contact. If the rootstock is thicker than the scion, it is better to align one side of the cambium, which makes it easier to graft successfully. Finally, wrap with plastic film tape and seal with wax.

2. Small-bud side grafting method

① Cutting the scion: With the bud of the scion facing up, make a diagonal cut at a 45° angle about 1 cm below the bud, then make a forward horizontal cut about 0.5 cm above the bud, cutting off the bud with a little xylem attached, and place it in a basin of clean water. The bud piece of a long-piece small bud is relatively thin, 1.2 to 1.5 cm long, longer than the small buds of ordinary budding.

② Cutting the rootstock: Do not cut off the upper part of the rootstock. At 10 to 20 cm above the ground on the trunk, cut the bark layer on a smooth side, requiring the cut surface to be smooth, with the depth just reaching the cambium, and the length of the cut surface just enough to hold the graft bud, then cut away 1/3 of the removed bark to facilitate wrapping and bud sprouting.

③ Inserting the bud and wrapping: Insert the cut bud piece into the rootstock cut so that the bases of the rootstock and scion fit tightly and the cut surfaces align, then wrap with plastic film tape, exposing the bud eye.

3. Single-bud side grafting method: Cutting the scion is the same as the single-bud cut grafting method; cutting the rootstock, inserting the bud, and wrapping are the same as the small-bud side grafting method.

4. Management of grafted seedlings

① Re-grafting: If 15 days after budding the graft bud is fresh and the leaf stalk falls off at a touch, this indicates that it has survived. Rootstock seedlings that have not survived should be re-grafted promptly; if too late, the rootstock bark will not slip, affecting survival.

② Cutting the rootstock: If the graft bud has survived, except for cut grafting, side grafting requires cutting the rootstock. Before sprouting, cut off the part of the rootstock above the graft bud to concentrate nutrients for the growth of the graft bud. However, the rootstock should not be cut too early, to avoid the cut being easily dried out by wind and damaged by freezing. For rootstocks that did not survive after overwintering, branch grafting can be used for re-grafting in spring.

③ Removing sprouts: After the rootstock of a grafted pomelo tree seedling is cut, a large number of sprouts tend to emerge from the base of the rootstock and must be removed promptly, to avoid the cut being easily dried out by wind and damaged by freezing.

④ Trunk setting: Pomelo seedlings are topped around the Beginning of Autumn, leaving a trunk height of 30 to 40 cm; generally, topping between the 2nd and 3rd nodes at the top of the first summer shoot is most suitable. Cultivate seedlings about 50 cm tall with 2 to 3 robust shoots evenly distributed.

⑤ Fertilizing: The principle for fertilizing grafted pomelo tree seedlings is frequent application of thin fertilizer. In drought, water once every 3 to 4 days; in the rainy summer, do good drainage work.

⑥ Disease prevention: For grafted pomelo tree seedlings, promptly control anthracnose, canker, and damage from leafminers, red spider mites, yellow spider mites, aphids, swallowtail butterfly larvae, and others.