Thai Lime trees are easy to grow providing you 1) allow the soil to dry out between watering so the roots don’t rot, 2) water and feed generously, 3) maintain humidity / avoid dry air (see below for details) and 4) keep these plants indoors over winter.
WATERING & FEEDING
When the top layer (couple of inches) of compost is completely dry then water the top of the pot generously until you get run-off out of the bottom. If you can, water with rain water. Water frequently in summer (typically once a week depending on the weather) and less often (roughly twice a month) in the winter. The most important thing is to check the compost regularly and only water if the top layer is dry. If in doubt, err on the dry side.
This plant prefers a humid environment, which is why we recommend standing the pot on a bed of clay beads in a saucer containing the run-off water. Ensure the water level is below the top of the beads, do not allow the pot to stand in the water. By using clay beads, you can ensure the roots are above the water (and won’t rot) but the plant benefits from the humidity created as the water in the saucer evaporates. If the air is dry, it is also a good idea to mist the leaves.
Feed with a specialist citrus feed at the same time as watering your plant, following the instructions on the packet.
POSITION
In winter, this plant should be placed indoors in a spot that gets direct sunlight but is not in a draught or near a radiator/fire because it does not do well in dry air.
In the summer, move the lime away from the window / glass during any heatwaves to avoid the plant being harmed by excessive heat. Once the plant is larger, it can be placed outside in a sunny spot any time the temperatures are consistently above 5°C.
POTTING ON & PRUNING
This Thai Lime can remain in its current pot for a couple of years and should only be moved to a larger pot when its roots have filled the current pot. It may eventually grow to 3m high and 2.5m wide after many years, depending on the size of pot it is in and on whether you prune it to a smaller size.
Once the roots have filled the current pot, you can transfer the plant to a new pot that is just one size up in the spring. Overpotting into a much bigger size pot risks root rot. At this stage, we recommend using a pot that can go outdoors so that you can place the tree outside from spring to autumn, bringing it in over winter. A deep saucer is useful so you can add a layer of gravel or clay beads. Alternatively you can use pot feet to raise the pot up above the saucer or tray.
If you are watering with tap water then use an ericaceous compost, or a specialist citrus compost. Otherwise, a good quality peat-free compost is fine but add 20% horticultural grit or sand to improve the drainage. The plants we supply have been potted in peat-free citrus compost.
This tree does not require much pruning. In late winter, you can remove any branches that are over-crowded and any that spoil the shape of the tree. In summer, you can pinch out the tips of any fast-growing stems to encourage branching.
PESTS & DISEASES
This tree is largely pest- and disease-free when grown in the UK but it may be susceptible to scale insects. Keep an eye out for small pale or brown bumps on the stems or alongside the main leaf vein, or a sticky residue (sap), or black soot that can build up on any sap. You can slide the scale insects off with your fingers and wipe the leaves with soapy water. A soapy wash every now and then is a good idea to reduce the chance of getting scale insects, to wash off any sticky sap / sooty fungus and to keep the leaves looking good.
You may get some leaf fall if the plant is over-watered or lacking nutrients or after the shock of re-potting or a sudden temperature chage. Don't panic! Carry on looking after your plant as instructed above and it should recover.
