Calamansi is a citrus fruit, a cross between the kumquat and the mandarin orange. Sour in flavour, the fruit is used extensively in Filipino cuisine. An easy tree to grow, the calamansi can be grown indoors or outside where there is no frost -- in zones 9 and above on the U.S. Department of Agriculture Hardiness Zone Map. The tree thrives in regions that are sunny and dry. Planted as a seedling, the calamansi bears fruit within two years.
Amend the soil in the planting area if it is either sandy or heavy clay. Use 3 inches of compost mixed into the top 6 inches of sandy soil. Clay soil needs amendments in a wider, deeper range. Dig up a 1-square-foot area to a depth of 1 foot and add 3 inches each of builder's sand and compost to the removed soil before replacing it in the planting area.
Test the soil's pH. Calamansi does best when the soil pH is 5.5 to 6.5. If you need to adjust the pH, contact your county cooperative extension agent for suggestions on which amendments to use.
Dig a planting hole that is the same depth at which the calamansi has been growing and twice the diameter of its root ball. Place the root ball in the hole and fill it with soil. The graft union -- the swollen area or diagonal scar on the lower trunk -- should sit at least 2 inches above the surface of the soil.
Water the calamansi slowly until the water puddles at its base, and keep the soil moist at all times.
Apply a 3-inch layer of mulch to the soil surrounding the calamansi, 6 inches from its trunk and spread 1 foot beyond the tips of its widest branches.
Fertilise the calamansi for the first time one month after you put it in the ground. Use 2/3 cup of urea combined with 2/3 cup of 16-20-0 fertiliser. Scatter it around the base of the tree, 6 inches from the trunk, and water after application. Repeat the application in four months. In the tree's second year, increase the amount of urea and fertiliser to 1 cup each. In the third year, use 1.36kg. of 12-24-12 fertiliser applied in the spring two months after the calamansi flowers and again after harvest.