Growing Cold Hardy Citrus
Think of Florida landscapes and two things come to mind: citrus and palm trees. As you travel along interstates from north to south Florida, pines common along roadsides are replaced with palms and citrus. Citrus is an important commercial agricultural crop to Florida and is also a great addition to the urban landscape.
Citrus are semitropical to tropical fruit that are fairly low maintenance and easy to grow, barring a severe freeze. There are many varieties that can be grown successfully providing fresh fruit in fall through winter months. After all, the citrus industry originated in north Florida along the St. Johns River until forced further south with the big freezes of 1894-95.
To be successful with citrus, select a sunny location with a well-drained soil. Don't plant citrus at the bottom of a hill or slope since cold air drains downhill. Planting on the south and southeast sides of a lake or any body of water provides additional protection from freezes. When planting, place the rootball two inches higher than the surrounding soil to insure positive drainage. Don't mulch around citrus because this holds in moisture around the trunk and promotes disease problems, especially a disease called foot rot.
Selecting Citrus for Northeast Florida
Citrus trees are grafted, meaning they are composed of two parts: a variety (scion) which produces the edible fruit on top of a rootstock. Most rootstocks in our area are used to improve cold hardiness. The most cold-hardy rootstocks include trifoliate orange, sour orange and Cleopatra. A local Jacksonville nursery, The Flying Dragon Nursery, uses the 'Flying Dragon' rootstock which is a selection of trifoliate orange. Other cold-hardy rootstock options with trifoliate orange parentage include 'Carrizo' citrange and 'Swingle' citrumelo. If you plan to grow citrus in a container, select a rootstock that might help reduce tree size. The container itself will help but some additional benefit might be gained by using a trifoliate orange rootstock. The most reliable dwarfing rootstock is the 'Flying Dragon' rootstock, but because rootstocks are produced from seed, there is some genetic variability in the dwarfing potential of trifoliate-type rootstocks.
Satusuma tangerine, grown in cool subtropical regions of Japan, is ideally suited for our climate. Satsuma has high fruit quality in regions with hot summers and cool winters so cannot be grown in south Florida. Satsuma is a mandarin type orange with loose rind and fruit sections.
There are 3 Satsuma varieties recommended for our area which include 'Owari', 'Silverhill', and 'Kimbrough'. Fruit of all of these have few to no seed. 'Owari' is the most widely available. This small to medium tree has a spreading/weeping growth habit, is a slow grower, and is very productive. 'Silverhill' is a more vigorous variety, is very productive and has a more upright growth habit compared to 'Owari'. 'Kimbrough', a Louisiana introduction, is a larger tree with a spreading growth habit and is thought to be slightly more cold tolerant than 'Owari'. Trifoliate orange is the preferred rootstock because it improves cold hardiness and causes dwarfing of the trees.
November through December are the peak times for satsumas. Fruit mature before the rind develops an orange color so occasionally sample one starting in late October to determine if they are ripe. Unlike other citrus, satsuma fruit hold poorly on the tree after ripening and should be picked promptly. If fruit is left on the tree too long after they mature, they become puffy or pithy and loose their flavor.
Use hand pruners to clip fruit when harvesting. When fruit is pulled from the tree, fruit may tend to "plug", leaving part of the skin on the tree. This will cause the fruit to rot and shorten the storage time.
There are several varieties of grapefruit that are divided into two main groups: white fleshed or pink-fleshed/colored grapefruit. 'Duncan' is an old standard variety, has very high quality white fruit, but has many seeds (30-70 per fruit). Harvest season is from December to May. Once grapefruit are mature, they hold well on the tree unless there is a severe freeze.
'Marsh' is a seedless variety that has a pale yellow flesh and is harvested from November to May. This variety is used commercially for juice production.
'Redblush' is a seedless variety used commercially for juice and cocktail products with ruby colored flesh. The peel has a pink blush and the flesh is pink to pale red. 'Star Ruby' is another variety with a deep red flesh but is less cold hardy that the other varieties.
Select those varieties that mature from early to late fall so that fruit will normally be harvested before we have a severe freeze. Those that have a harvest season ranging from October to January include navel, 'Parson Brown', 'Ambersweet' and 'Hamlin'. 'Hamlin' trees are very cold hardy and prolific. These small round fruit are excellent fresh or for juicing. Fruit stores well on the tree but is susceptible to splitting, especially following high rainfalls. 'Parson Brown' is a medium round fruit that is an excellent fresh or juice orange that can be harvested slightly earlier than 'Hamlin'. It's only drawback is its seediness and lower fruit yields as compared to 'Hamlin'.
'Ambersweet' was once touted as the most cold-hardy of this group. It has been reclassified to moderate cold hardiness. Fruit looks like a navel orange, peels easily, and can be used as a fresh or juice orange. Based on conversations with gardeners growing this variety, give the tree time since the fruit quality improves with tree age.
Navel and Red Navel are more labor intensive for home gardeners. These require more precise irrigation and nutrition management. Fruit are large round that are seedless and peel easily.
Other popular choices include the Myers lemon and limequat. The Myers lemon is not a true lemon but is a cross between a lemon and mandarin which makes it more cold hardy than the true lemon. The fruit is larger than a lemon and has a milder taste. Likewise, the Tavares limequat is a good substitute for limes because it is more cold hardy. Fruit are about the size of a kumquat.
Citrus Growing Tips
Citrus thrive in our sandy, well-drained soil. Irrigate as needed, especially when there are fruit on the tree. During hot, dry weather, water twice a week in the absence of rainfall. Provide even watering throughout the growing season to prevent fruit from splitting when we start to get heavy rainfalls.
Good fertilization practices are a must to successful fruit production. After planting, add a citrus fertilizer (6-6-6 or 8-8-8) two weeks after planting and then make frequent light applications every six weeks through September. Place the fertilizer in a three-foot diameter circle around the tree. For the first three years, never use a fertilizer higher than an 8-8-8 analysis unless it's a slow release nitrogen fertilizer. Once trees are four years old, increase the amount of fertilizer up to but not more than 1.5 pounds of nitrogen per tree per year. That means to apply 0.80 or 1 pound of a 6-6-6 or 8-8-8 fertilizer, respectively, three times a year. Broadcast the fertilizer in an area twice the diameter of the tree canopy. Do not fertilize citrus between October and February 1.
Remove any shoots growing below the graft union. These are coming from the rootstock and are typically more vigorous than the scion. If allowed to develop, they can overtake the tree. Very little pruning is required for citrus. Prune as needed to control shape or remove diseased or rubbing branches. If fruit loads are extremely heavy, remove young fruit to avoid limb breakage. Removing excess fruit may also reduce the chance of getting a heavy crop one year and none the next. This is a common occurrence with many fruit trees and is referred to as 'alternate bearing'.
For more information on growing citrus visit the University of Florida web site at http://edis.ifas.ufl.edu/.