Watering:  There are several ways to water/irrigate curry leaf plants.  Any method may be adopted, some are better than the others, easier, requires no additional work etc.  If you have a small curry leaf plant in a or 2-gallon pot, it will benefit if you replant into a slightly larger pot, 3- or 5-gallon pot.  You may choose to water every day using a flower can or just a hose, which is fine.  Sometimes you may forget to water the plant, and this might stress the plant, if you are gone for a few days, it may reach a point when the plant will never be able to recover!

Under these circumstances it might be wise if it is on a drip irrigation line.  You can insert or add an emitter to the newly planted curry leaf plant, make sure that it waters every day to begin with.  Then every other day is ok.  If you live in the desert South-west, it is important to place the pot in a shady area.  It can reach 115 F in Phoenix, AZ and Yuma, AZ.  Curry leaf plant does very well in partial shade, or even complete shade (if it gets some diffused light).  Once the plant is out of the pot in the soil/dirt it will be able to grow with less frequent watering and be able to tolerate several hours of sunshine.  

The third method is to make a donut around the plant. When it is time to water, you use a hose and fill the donut with water.  The water slowly seeps into the soil.  This method uses more water compared to the drip, plus there is a lot of water that is lost due to evaporation.  With water scarcity in the desert South-west, it may not be the best method to irrigate.  Avoid stagnant water near the tree trunk!  It is called the ‘Collar’ region, it is most susceptible to either pest or pathogen.  Shovel some soil/dirt so the place is mostly dry!

Careful!  Adding a shrub or tree to an existing drip line is good, as long as the zone specifically waters trees or shrubs.  It is not wise to add a tree or shrub to a zone that waters ground cover, flower beds or vegetables.  These have shallow roots, and require frequent watering, whereas a curry leaf plant that is planted in the soil doesn’t require such frequent watering cycles.  If you still choose to add it to a zone that waters vegetables, you may force the roots of curry leaf plant to grow close to the surface of the dirt.  This prevents the roots from growing deep into the soil, thereby using the moisture that is deeper.

Careful!  The second thing that one should watch out for is the number of emitters that the plant gets.  A newly planted curry leaf plant that came from a 1 to 3 gallon or even a 5-gallon pot, may be happy with a single emitter.  As the tree matures and grows larger, it will be good to add more emitters.  You may increase to 3 emitters per tree, spaced equally around and away from the trunk.  Once it grows about 5 feet tall, it would benefit from increasing from 3 to 5 emitters per tree.  The anchor roots are close to the center of the tree, but the roots that absorb water are at the periphery of the tree, see figure XX.

Choosing emitters:  There are several different kinds and brands of emitters available on the market.  There are flag emitters, button emitters, spider emitters (which are adjustable) and pressure compensating emitters.  The first two are the most economical, they usually put out a specified flow rate example – 0.5, 1.0 or 2.0 gallons per hour (gph).  The spider emitters are adjustable, they can be adjusted anywhere from zero to 5.0 or even 10 gallons per hour (read label).  These can be very useful, though it is not as economical as flag or button emitter.  Lastly the pressure compensating emitters are the most expensive, they put out the same amount of water, meaning they are not adjustable.  The advantage is that there is no variation in application rate between the first or the 50th emitter on the line! Meaning all emitters on a specific line, will put out the same amount of water.  (With the other button, flag and spider emitters, the ones close to the valve may put out slightly more water than the one furthest away, as the pressure reduces further out you are!)

When to water:  This is always the most challenging to answer, as there are so many variables that decide the amount and frequency of watering cycles.  The type or soil, the location of the curry leaf plant, is there partial shade, is it close to the lawn, does it have a layer of mulch on the soil etc.  In general, sandy soil doesn’t soak up much water.  Clay soil soaks up a lot more water.  Plants that are in partial shade require slightly less water; mulching reduces water loss through evaporation from the soil.  One good way to test if there is enough water is to use a tool to check.  Curry leaf plants stay happy if the soil is adequately watered to a depth of 12 to 24 inches from the surface of the soil.  Sometimes you can get by with 18” of soil being wet.  Anything below 3 feet is not useful to the plant.  

You would like to use a moisture probe, like the ones you see in the home improvement stores.  They may help, but an even better method is to use a long screwdriver or a smooth rod about 2 to 3 feet in length about pencil thick.  It must be smooth; you shouldn’t use a rebar for example. (Agricultural extension offices and/or Master gardeners usually sell these probes, usually $20) One day after the curry leaf plant was watered, use the tool to push it down the soil.  You may have to try this at different spots, as the area around the emitters are the only places that will be wet.  As you push this tool, check where it stops.  That is the depth to which your water has reached.  You may wonder how reliable this method is, try it, you will be surprised at how good it is.  Many professionals use this tool to check agricultural fields.  As I said before you should be able to push it to a depth between 12 to 24 inches.  Try several places around the tree, if you can push the tool about 8 inches, you must water longer!  On the other hand, if it goes down to 36 inches, then you can cut down your duration of watering.