Mandarin trees grow easily from seed, but a seed-grown tree can take several years to be large and mature enough to produce fruit. While not every type of mandarin comes true from seed (that is has fruit that’s the same as the parent) the Emperor variety does come true and crops relatively quickly. Most citrus, including mandarins, are grafted or budded onto disease-resistant two-year-old rootstock. Grafted plants should fruit within two years of purchase.
1. Save the seed. Keep a few seeds from a large, juicy mandarin. Gently wash the seed clean, allow it to dry on a paper towel and then sow the seed or store it. Fresh seed is more viable (that is more likely to grow) than older seed. Seeds are best planted in spring or early summer. If seed has to be stored keep it in a labeled envelop in an airtight container.
2. Sow the seed. Sow the seed into a container filled with seed-raising mix (available in bags from garden centres or hardware stores). Seeds can be sown in a small (10cm) pot with one seed per pot. Moisten the mix before sowing the seed then gently push the seed about 5mm deep into the mix and cover it over. After sowing, water the pots with a seaweed solution (follow application rates on the container).
3. Keep warm. Keep the pots warm either in a glasshouse or place them in a foam box covered with a sheet of glass or plastic to form a mini glasshouse. Keep the box in a warm well-lit spot but not in direct sunlight.
4. Keep moist. Mist the seed-raising mix so it doesn’t dry out (it should be moist but not soaked). Water gently using a rose attachment on a watering can or hose once the shoot appears. Germination normally takes around seven to 10 days.
5. Allow to grow. When the seedling is about 5cm high, water with a dilute liquid plant food. Repeat the fertiliser application every 14 days during the warmer months of the year (follow directions on container). At this stage, if the weather is warm, the pot can be moved into a sheltered but sunny spot. Outside it will need extra water as it will dry out more quickly than in the sheltered glasshouse.
6. Protect from pests. Snails and slugs may attack seedlings. Protect the little plants with a few pellets of iron-based snail and slug bait. Check the leaves for other pests including aphids and caterpillars. Squash any that are found.
7. Repot. When the seedling is about 10-15cm high with a well-developed root system it is ready to go into a larger container (15cm diameter) with fresh potting mix. Continue to repot into larger containers as the plant grows and its roots begin to fill each new pot.
8. Plant out into the garden. After about two-year’s growth the seedling should be a robust shrub, which can survive in the garden. If in doubt, continue to grow it in a container until it is around 30cm high or larger.
9. Fruit production. Seed-grown mandarins may take four to seven years to flower and fruit. Young trees with weak branches should be discouraged from fruiting by removing flowers and tiny fruit. Flowering occurs in spring with fruit forming in summer and ripening in early autumn.