I posted this information under the "Off Topic Forum," in answer to a particular question, but I will post it here as a stand alone post.
To help answer questions towards methods of getting citrus trees to flower, especially when cool temperatures cannot be given. I've read elsewhere, a post asking how to get citrus buds to "break dormancy" so that the dormant "floral buds" will begin to flower. Advice given included to provide the tree with cool temperature stress, drought stress, or light stress, (the latter I never heard of). To begin with, there is no such thing as "floral bud dormancy" in citrus trees, because initially there are no flower buds. All citrus buds are vegetative buds, that will produce new foliage. What cold stress and drought stress accomplishes is to change a foliage bud into a flower bud by a biochemical process called differentiation. Differentiation = to change from one type of organism to another type of organism. In other words, the cold treatment or the drought treatment biochemically changes a bud that would have produced foliage (leaves) into a bud that will now produce flowers. Normally in temperate regions, this change is caused by the tree experiencing a period of cool weather. However, in many regions of the world there are no periods of cool weather to promote differentiation. In these regions flowering is accomplished by the dry season, where the tree experiences drought stress. Water stress can play a role in flower induction. In the hot and humid lowland tropics, there is little seasonal variation in temperature. In these areas, flowering is usually rather continuous throughout the year. Greater flowering intensity usually occurs when rainfall returns after a period of dry weather. Water stress has been used for more than a century in Mediterranean countries to stimulate flowering in lemons. By withholding water during certain periods, the timing of flowering can be altered so fruit can be harvested at a time of higher prices (this is the case with 'verdelli' lemons), or drought stress can be used to just promote a tree to flower. It is important to determine the optimum level of stress at which irrigation should be started after the dry period. Too little stress can promote an inadequate flowering response. Too severe a stress can cause excessive leaf and fruit drop. Moderate water stress is recommended to induce sufficient flowering without excessive fruit drop, if fruit is present on the tree. For trees without fruit, this of course is not a concern. In Sicily, to promote the blooming of Lemon trees, water is withheld until the trees show wilt, then water is once again given and the trees put forth a nice bloom. Water stress can also be accomplished in container trees, by moderately withholding water to lower levels causing a stress to the tree. I have seen, more often than I would like, a few of my citrus trees bloom forth, after I have inadvertently failed to water causing the tree to became wilted. In one case quite wilted. - Millet
