Frequently Asked Questions

Special thanks to Malcom Manners for letting me use the following that he wrote. His home page is here. He teaches at Florida Southern College Department of Citrus and Environmental Horticulture.

Q: What is grafting or budding?
A: Grafting is any method which surgically connects a part of one plant to a part of another plant; the two then grow together to become a single plant. The top part, which will produce the branches, leaves, flowers, and fruit, is known as the “scion” (pronounced sigh-on). The lower portion, which produces the root system and the very bottom part of the trunk, is known as the rootstock, understock, or simply “stock.” The scar where the two are joined, and which may remain visible throughout the life of the tree, is the graft union, bud union, or simply “union.” Budding is simply a method of grafting in which the original scion had a single axillary bud eye on it (as opposed to a bigger scion with more bud eyes). An axillary bud, known to budders as an “eye,” is the tiny green bump just above the point of attachment of a leaf, on the stem.

Q: Why would you want to graft a citrus tree?
A: Grafting (including any method of budding) can give a tree several advantages.
1. Oranges and grapefruit are highly susceptible to foot rot disease, caused by Phytophthora citropthora and P. nicotiana. Some rootstocks offer considerable resistance to that disease. So on infested land, it’s important to use such a stock.
2. Rootstock variety has some effect on the strength of flavor of the fruit, the sweetness, total yield of the tree, and cold-hardiness of the tree.
3. Some rootstocks have resistance to certain virus diseases, nematodes, or other problems.
4. Some citrus scion varieties are difficult to root from cuttings. Grafting is a convenient way to reproduce such trees, since virtually all citrus varieties are very easy to graft. A grafted tree using a mature scion will not have the years of juvenility that a seedling would have.

Q: Can you graft more than one variety to the same rootstock, for a “fruit cocktail” tree?
A: Yes, it can be done. Just grow your rootstock tree big enough to have several side branches, and graft (bud) a different scion to each branch. Realize that there are some potential problems:
1. If any of the scions you use has a virus, it will move into all the other varieties. And while some varieties may be tolerant and symptomless, others may show strong symptoms or even die. For example, if you grafted an orange scion onto a grapefruit limb, and the orange scion happened to have tristeza virus, it would kill the grapefruit.
2. Even if all the parts are virus-free, it’s likely that some varieties will be more vigorous than others, and will “take over” the tree, crowding or shading out the others. Tangeloes and lemons tend to be the most vigorous, followed by grapefruit, then oranges, then tangerines, and Key limes are least vigorous.

Q: What qualities will a rootstock give to a scion?
A: The rootstock can provide its scion with several qualities.
1. Cold hardiness. In areas where citrus is grown outdoors, but where frost is a potential problem, this can be important. While no stock gives extreme hardiness (no, you’ll never be able to grow orange trees outdoors in Ohio!), the difference can be several degrees of hardiness. On the other hand, some stocks reduce the hardiness of the scion. In approximate order from most cold-hardy to least, here are the common stocks used in Florida and California:
Poncirus trifoliata (including “Flying Dragon’), sour orange, sweet orange, citrumelos (including ‘Swingle’). These three enhance cold-hardiness noticeably.
‘Carrizo’ and ‘Troyer’ citranges; ‘Cleopatra’, ‘Sun Chu Sha’, and other mandarins. These stocks have little effect, one way or the other, on hardiness.
Rough Lemon, Volkameriana, Rangpur. These stocks may give a tree that is less cold-hardy.
2. Tolerance to disease problems.
3. Enhanced (or diluted) flavor.

Q: I’ve heard that grafting a citrus variety can affect the flavor. Does that mean that if I graft an orange onto a grapefruit rootstock, the oranges will acquire a grapefruit flavor?
A: No, each variety will always have the same basic flavor, regardless of rootstock. But the rootstock chosen will affect the intensity of the flavor, as well as the sweetness-to-sourness ratio. Generally, less vigorous rootstocks (Poncirus trifoliata, Sour orange, citrumelo) stocks give a richer-flavored fruit. Very vigorous stocks (rough lemon, volkameriana, Rangpur) give a more bland, diluted-tasting fruit. In the questioner’s example, grapefruit roots will cause the orange scion to produce bland-flavored fruit.

Q: Do citrus come true from seeds?

A: Most citrus come absolutely true from seeds. They do this by producing "nucellar embryos," which are not produced by sexual fertilization at all; rather, they are tiny "tissue cultures" of the mother plant, packaged within the seed. The zygotic (sexually produced) embryo usually fails to survive in such seeds, so you have a seed that may make several seedlings, all of which are identical to their mother. There are exceptions. Some varieties are monoembryonic, meaning that they have ONLY the sexually produced embryo, so won't come true. Examples are 'Temple' orange, 'Clementine' mandarin, 'King' mandarin, all of the citrons (C. medica), and all of the pummelos (C. grandis). Also, in varieties which are chimeras (partial mutations, where one layer is mutated but another is not), the seedlings may be nucellar, but may not match the parent. An example is 'Thompson Pink' grapefruit, in which the seedlings will all be identical, but they'll be 'Marsh' white grapefruit, rather than Thompson, since the layer that produced the seeds doesn't have the mutation for pink. Navel oranges do produce nucellar seedlings, but they often show minor variations. So virtually all the seedlings will be navels, but they may vary slightly from the parent and from one another.
But in the case of the vast majority of oranges, grapefruit, lemons, limes, and mandarins, completely true-to-type offspring is the norm.

Q: I’ve heard that oranges from seed may take 10 or more years to bear their first fruit. If I grow an orange from seed, will grafting it make it bear fruit sooner?
A: That depends on what you mean by “grafting it.” If you plan to cut a scion from your seedling and graft it to another root system, then no, you’re not likely to shorten the time to bearing significantly. But if you have access to a mature, bearing tree, from which you could cut a scion, and you graft that mature scion onto your seedling, using your seedling as the rootstock, then yes, that would result in a fast-bearing tree. This is how commercial citrus trees are produced -- mature scions are grafted to young rootstock seedlings. They’ll often bear a fruit or two in the 2nd year, and be in excellent production by the 5th year.

Q: I’ve heard that seedling oranges are sour, and need to be grafted to make them sweet. Is that true?
A: No. The “sour orange” is Citrus aurantium. It is also known as the ‘Seville’ orange, famed for its use in English marmalade. Sweet orange is Citrus sinensis, an entirely different species. Sour oranges will always be sour, and sweet oranges will always be sweet. In areas of the world where tristeza virus is not present, sweet orange grafted to sour orange rootstock gives sweet oranges of exceptionally good quality. But the tristeza virus has made that combination rarer and rarer, recently, since it kills the trees. Sour orange can be grown as a scion, but its fruits will always be sour, regardless of the rootstock used.

Q: I want to grow a citrus tree in a pot, indoors. Should I be concerned about grafting, or about which rootstock is used?
A: A citrus tree grown from a rooted cutting or air layer will probably be just fine in a pot. If the cutting came from a mature tree, it will bear fruit while still small. So that’s a great improvement over growing from seed. But if you can get a grafted tree on ‘Flying Dragon’ roots, it will be a strongly dwarfed tree, which will produce fruit of very high quality. Grafted trees on other root systems may be just fine in a pot, as well, but they won’t have the extreme dwarfing characteristic of the ‘Flying Dragon’.

Q: What are the good and bad characteristics of the various rootstocks for citrus?
A: There is an old saying among Florida citrus growers, that you choose your rootstock based upon how you want your tree to die. A pessimistic approach, but it’s true that every rootstock out there has disadvantages that, under the right conditions, could result in loss of the tree. On the other hand, each stock has some advantages, that might cause a grower to select it for a specific set of soil, climate, or cultural circumstances. This list will give the advantages and disadvantages of the commonly used stocks, under Florida conditions, with notes on their California performance, where I know them. Note that blight disease is not known to be in California, and tristeza virus is present in some parts of California, but not others. Both diseases are well-distributed around Florida, and should be assumed to be present everywhere in the state.

Poncirus trifoliata ‘Flying Dragon’. The most extremely dwarfing stock available. Excellent for pot culture or for small lawns where you want a big shrub, rather than a full-size tree. Highly cold-hardy. Fruit will be smaller than average, but richly flavored. Not susceptible to blight disease. Tolerant of most virus diseases, but highly susceptible to exocortis viroid. Commercially budded trees will be free of exocortis, so that may not be a concern. Requires a fairly acid soil (pH 6.2 or lower).

Poncirus trifoliata (‘Large-Flowered’, ‘Roubidoux’, or any other variety other than ‘Flying Dragon’). Smallish, but not really dwarf trees. All the advantages and disadvantages of ‘Flying Dragon’, except that they will be extremely susceptible to blight disease (a problem in Fla., not in Calif.). Needs an acid soil (pH 6.2 or lower).

Sour Orange (including ‘Bittersweet’ and ‘Smooth Flat Seville’). Trees of average size. The very best fruit quality (flavor and color). Excellent cold hardiness. Resistant to most diseases BUT highly susceptible to tristeza virus, which is killing trees by the millions in Florida. Therefore NOT recommended for outdoors in Florida. Elsewhere it may be ok, depending on whether the virus is present in the area. Tolerant of more alkaline soils than most other stocks.

Sweet Orange (as a rootstock). Excellent cold hardiness. Excellent fruit quality. Resistant to all of the common virus diseases and excellent resistance to blight. Highly susceptible to Phytophthora foot rot, which is the only factor that prevents its being more popular in Florida.

Citranges (hybrids of P. trifoliata by sweet orange). Includes ‘Carrizo’ and ‘Troyer’. Average size trees, fruit of average to good quality. Heavy yielding. Average cold-hardiness. Susceptible to blight disease and exocortis viroid. Need soils with a pH of 6.5 or lower

Citrumelos (hybrids of P. trifoliata by grapefruit). Includes ‘Swingle’. Trees will be slightly smaller than average, but not truly dwarfed. Fruit of excellent quality, approaching that of sour orange. Trees fairly cold-hardy and with some resistance to blight disease. Tolerant to most other diseases. Some varieties show a long-term graft incompatability. ‘Swingle’ is by far the most popular stock in Florida in recent years, because its advantages tend to outweigh its disadvantages. Need acid soils with a pH of 6.2 or lower

Rough Lemon, Volkameriana, Rangpur lime. These are three different species, but in the field, they behave very much alike. Extremely vigorous, producing huge yields per acre, and starting to bear a year earlier than most other stocks. Fruit is large, early-maturing, but dilute and relatively bland, compared to other stocks. All of these rootstocks produce a very large tree that is less cold-hardy than most, and more susceptible to blight disease than most. Those two problems limit their usefulness. Tolerant of neutral to slightly alkaline soils, but prefer slightly acid.

Mandarins (including ‘Cleopatra’ and ‘Sun Chu Sha’). Big, vigorous trees. May take a year or two longer to come into bearing, and may take several extra years to reach full bearing potential, compared to other stocks. Fruit will be smaller than average, later maturing than average, but fruit quality will be rich and excellent. Tolerant of most diseases. Fairly cold-hardy. Popular under large-fruited mandarin hybrids (tangelos, Temple, etc.).

MrTexas comments on rootstocks for the Houston, TX area

Malcom gives excellent advice on rootstocks for the zone 9b citrus belts of Florida, California, and Texas. For the marginal areas in zone 8b/9a like where I live near Houston, TX, the only rootstocks that should be considered are trifoliate or flying dragon. Our area needs the extra cold hardiness of these rootstocks. Any others will be prone to be more vigorous and growth during the winter months. In this year's late March freeze to 19F, most unprotected trees on anything but trifoliate or flying dragon froze. Be wary of trees grown in the Texas Valley for sale in Houston, TX. Most are on sour orange and will freeze out in Houston unless protected. Search out trees grown in Houston for the Houston market, especially those grown by Treesearch as these will be on trifoliate rootstock. The primary rootstock for the Texas citrus belt continues to be sour orange. The brown citrus aphid the primary vector for tristeza virus is not in Texas yet. No other rootstocks have been found to be better for the Texas Valley soils.

Q: What is the best pH for a citrus tree?

A:The ideal pH for a citrus tree is 6.0 to 6.5, if it's on citrus roots, or 5.5 to 6.0, if budded/grafted to Poncirus roots or one of the Poncirus hybrids (citrumelo, citrange, etc.) Ideally, you should have your soil tested. A local extension office may do it for you, or even a local college or high school with a chemistry dept. Or you can buy fairly cheap pH meters or even cheaper pH testing paper (not very accurate, but perhaps close enough). For a meter, the traditional way to measure pH is to mix a soil sample with an equal volume of water, let it sit for about 1/2 hour, then test it with your pH meter.
If the pH is too low, you'll need to bring it up with some form of lime. If it's too high, you bring it down with acid-forming fertilizer, sulfur, iron sulfate, aluminum sulfate, etc.

Light-color leaves are more likely to be caused by too-high pH than too-low, although if the pale green is solid (same color veins as background, no striping, etc.), it seems likely to be more due to a lack of nitrogen, than to a pH problem. If adding nitrogen fertilizer does not fix the problem, and the newer leaves remain pale yellowish green, with no pattern, I'd suspect sulfur deficiency -- many commercial fertilizers contain no sulfur.

Vinegar, lemon juice, etc, are pretty much worthless for soil pH management. Yes, they are acids when you use them. The problem is that as they biodegrade in the soil, they cease to be acidic. So the effect is very short-term.

In an alkaline soil (too high pH), citrus trees tend to develop deficiency symptoms for iron (green veins on an otherwise pale yellowish leaf), manganese (green veins with green borders spreading out from the vein, on the leaf, on an otherwise pale yellowish leaf), zinc (same as manganese but the leaves are also dwarfed), or Magnesium (an inverted "V" or "Christmas-tree" shaped area of green at the base of the leaf, with the upper/outer parts of the leaf yellowish or orangeish. Fe, Mn, and Zn deficiencies will be seen mostly on the youngest (top) leaves on the plant; Magnesium deficiency tends to show up first on the oldest (lowest) leaves.

Too-low pH (acidic) soils often result in a plant that looks perfectly healthy and normal, with dark green leaves. But the plant just doesn't grow vigorously and doesn't make much fruit. It's stunted, overall.

Q: My 10 year old 4 foot tall indoor grown seedling citrus tree hasn't had a bloom yet, what is wrong?

A:10 years may be long enough, but 4 feet tall from seed is the problem. Citrus trees, like most plants, don't measure their maturity in years, as do humans; rather, they measure it in number of nodes (points where the leaves are attached to the stem) from the original seed. So in a grapefruit tree, to get enough nodes along the stem, you usually need a tree 15-20 feet tall. If you keep pruning it to keep it indoors, it will never get there. Say you have an 8' tree at node 247. Assume that grapefruit starts flowering on node 589. (I'm making these numbers up; no one, to my knowledge, has ever counted the exact numbers for grapefruit, but we do know that citrus works this way). Now assume you prune your tree back to 4 feet. Now you're back to, say, node 120. When it grows again, it will start counting at 121, 122, etc. With continuous pruning, it may never get around to making mature wood.
There are a few ancient seedling groves left in Florida, and even on those 100+ year-old trees, if you cut too much off the tops when pruning, they stop bearing fruit until they get tall again. The way around that, for indoor growers, would be to:

1. graft or bud a mature bud (from some other tree) onto your tree. Such scion buds "remember" their node number.

2. Take cuttings or air layers from the very top of your seedling tree. Once rooted and established, discard your original big plant, and grow the new plant. It will start counting at whatever node number it was on when you took the cutting. Grapefruit are not the easiest plant to root from a cutting, but air layers often work.

Q. How can I air layer a citrus tree?

Air layers work best with a stem thicker than a finger -- maybe thumb size. But thinner stems can be layered if you're very careful not to break them. It's easiest to work when the plant is actively putting out new growth, since the bark will "slip," meaning it will peel cleanly away from the wood. Cut a ring around the stem, cutting through the bark to the wood. Don't go deeply into the wood. You can use a knife or the blade of a pruning clipper. Then cut another ring about 1/2" to 1" above (or below) the first ring. Then cut a vertical slice to connect the two rings. Now (assuming the bark is slipping) you can peel a ring of bark off the stem, the whole way around, and 1/2-1" high, depending on where you made your cuts. If the bark is not slipping, you may need to whittle the bark off, the whole way around. In any case, the goal is to girdle the branch -- completely remove the bark the whole way around, while leaving the wood intact. Some people apply a rooting hormone powder at this point, around the upper edge of the wound, where the bark and wood come together. With citrus it is not generally necessary, but may be helpful. The roots are all going to come out of that point where the bark ends, at the top of your wound, so there is no benefit in applying the material anywhere else. Now the wounded area needs to be wrapped in some moist, fibrous, aerated material. Long-fiber sphagnum moss seems to work best (available at many garden centers). Take a wad of it and soak it in a container of water, until it's quite saturated. Then squeeze the ball to remove excess water. You want it quite damp but not dripping. A compressed ball of the material (squeezed in your hand) should be tennis-ball or baseball-sized for a finger-thick stem; maybe softball size for a thumb-thick stem. Wrap the moss all around the wound, covering the wound thoroughly. While holding the ball of moss in place, wrap it with a piece of aluminum foil, perhaps 18 inches long. Wrap it tightly above and below the moss ball, and squeeze it over the ball itself. In 4-8 weeks, the stem should fill the moss ball with new roots, after which it can be clipped off, just below the moss, and planted up as a new plant.

FAQ.htm