There are two basic reasons for your citrus wilting: not enough water or too much water. Under watering puts the plant in stress mode, causing leaves to wilt and lose green coloring. Over watering means that the roots are constantly soaking in water, depriving them of oxygen. This also will cause the plant to wilt. The amount of water citrus trees need depends on several factors: temperature and humidity, amount of wind and whether the citrus is growing in pots or the ground. Giving citrus trees the right amount of water is simple.
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Insert a small spade approximately 4 inches into the soil at the base of the citrus and turn the soil. If the soil is damp, the tree does not need water and has, in fact, possibly received too much water. If this is the case, don't water again until the soil is dry 6 inches deep into the soil.
Make a circular basin around the base of the tree. The basin should be at least 14 to 16 inches in diameter for a small tree and up to 26 to 28 inches in diameter for a large tree. Pile dirt around the edges of the basin so the basin can hold quite a bit of water. Soak around the citrus if the ground is dry 4 inches into the soil. Allow a hose to soak the base of the tree for 10 minutes.
Check the soil at the base of the citrus the next day, especially if the temperature has been high and or there has been a fair amount of wind (wind will dry out the citrus). If the soil is dry 4 inches deep, soak again for another 10 minutes.
Check the soil every two days or so, watering only when the soil is dry at 4 inches depth.
Soak a potted citrus until water comes out of the bottom of the pot, but do not leave the pot in standing water. The tree should be no more than twice the height of your pot for proper root development.