HOW TO GROW AN ORANGE TREE FROM SEED
Growing orange trees from seed is surprisingly straight forward, and something that anyone can do if they have a warm, sunny windowsill. Getting the seed is probably the hardest part of the whole operation. You can either buy on-line through a specialist supplier or, if you only want a few, collect your own from shop bought fruit.
Place the ‘clean’ seed into a glass of water and discard any that immediately float to the surface as these will not be viable. Smaller seeds may rise to the surface as air bubbles form on the surface of the seed coat.
If you have a variety of seed sizes you may also wish to discard any that look undersized as these are unlikely to have a large enough store of energy required for successful germination. Once you have selected your seed it can be dried off and stored in an envelope until required.
Orange seed – like all citrus – have a natural dormancy period and so will require a period of cold temperature in order to initiate germination. They will germinate without this cold period but results will be poorer.
Luckily, most citrus fruits are transported using a cool-chain system so they have already been 'pre-chilled' before they reach you. If not, this can be overcome by placing the seed into the vegetable compartment of any household fridge and left for a few weeks. First, secure the seed into a paper towel by folding the towel it back on itself a couple of times, then place into a plastic bag or sterile food container before leaving it in the fridge.
After approximately three weeks - although they can be left in there for a month or so should they need to be – they can be removed from the fridge ready for potting on. Soak the seeds for a couple of hours or so before planting them into 2-3 inch pots. Only sow 1 seed per pot using a good quality, free draining soil based compost such as John Innes seed or No 1, then water in..
If you can, place the pots into a heated propagator at a temperature of 16 degrees Celsius, otherwise transfer them to a warm, bright position such as a kitchen windowsill. Water periodically so that the compost doesn't dry out, but make sure that the compost is never left waterlogged either.
The newly emerged seedlings can be left in their pots for a further 3 – 6 months depending on how they develop but once they get to about 4 or 5 inches they can be potted on to the next size pot using a John Innes ericaceous mix or No 2 potting compost. So long as there are no frosts predicted the young orange plants can be put out side to harden off over the next two to three weeks.
During the growing period they can be regularly watered and feed with a water soluble fertilizer once a week. You can often get yellowing of the leaves with orange plants due to chlorosis but this can be dealt with by feeding an acidic plant food.
Unfortunately oranges are not particularly cold hardy although they will tolerate temperatures as low as 4 or 5 degrees Celsius for short periods without to much trouble.
For northern European countries it is best to keep all oranges under protection during the winter periods, but once the threat of frosts are over they can then be hardened off for a couple of weeks before spending the rest of the growing season outside in the full sun.