Citrus Problems, Why Citrus Fruit Drops and Flowers Fail to Develop

lime flowers becoming fruit

Is your citrus tree dropping its fruit before they reach full size, or even worse, dropping the flowers before fruit even begin to form? This problem can happen to oranges, lemons, lime, grapefruit, mandarins and all other citrus.

Trees photosynthesise to produce carbohydrates such as sugars which they store as their energy source. They can only store a finite amount, which they use to drive the growth of new leaves, branches, roots and stem. Fruiting requires a tree to divert its finite energy resources away from these vital activities into the production of flower buds, flowers and fruit.

Fruit development involves pollination followed by fertilization, growth, maturation and ripening. This process takes between 6-7 months in warmer areas, requiring a considerable amount of the trees energy resources as a result.

Trees are capable of managing their own resources, and will re-divert them in cases of emergency…

Fruit Drop and Plant Stress

In regions where citrus produce a single crop each year, they go through a specific sequence of growth phases as follows:

  1. Bud formation and flower initiation (mid winter)
  2. Flowering and fruit set (early spring)
  3. Fruit growth – cell division (late spring to early summer)
  4. Fruit growth – cell expansion (mid summer to early autumn)
  5. Fruit maturation (late autumn to winter)

The exception to this is in regions where multiple citrus crops are produced throughout the year. In these cases, different growth phases will be occurring simultaneously.

A citrus tree can manage its crop load quite effectively, and will only carry as much fruit as it can support. It’s natural for all citrus trees to drop excess small fruit and young blossoms in early spring to prevent overproducing.

There’s no need to be too concerned about flower drop, as a citrus tree only needs 1% to 2% of the blossoms to produce a good crop, and sometimes even less than 1% is enough.

If a tree gets stressed because it doesn’t receive enough water during hot, dry windy weather, of if it is starved of nitrogen because it hasn’t been given adequate fertilizer, the fruit drop will be much heavier in spring. There can also be a minor amount of fruit drop in summer under stressful conditions.

Solution: Provide sufficient water, and water more often during hot weather and strong winds. Feed citrus with a balanced fertiliser at the start of spring (September in the Southern hemisphere,  March in the Northern hemisphere)

Flower and Fruit Drop in Citrus and Potassium Nutrient Deficiency

Where citrus trees are bearing heavy crop loads, fruit drop can be exacerbated by low potassium levels.

Potassium, also known as potash (represented by the chemical symbol K on fertiliser labels which state an N-P-K or nitrogen-phosphorus-potassium ratio) is a primary macronutrient which is necessary for flowering and fruit formation. Next to nitrogen, plants absorb potassium in greater quantity than any other nutrient. Without potassium, trees stop flowering and fruiting, that’s what happens when they’re not fed regularly.

Before any smug horticulturist proclaims to you that potassium is not directly responsible for flowering and fruiting, let me say that as a horticulturist and biochemist, plant chemistry, like the chemistry of all living things is complex, but certain inputs are necessary to produce certain outputs, and the references I’ve cited at the end of this article support my statements!

To get into the science, Potassium (K) is Important for water, nutrient and carbohydrate movement in plant tissues. It also activates enzymes which facilitate complex chemical reactions within the plant – such as the production of starch, protein and adenosine triphosphate (ATP). The role of ATP is to transports the energy necessary for all cellular metabolic activities in all living organisms, and in plants the production of ATP can regulate the rate of photosynthesis.

Potassium also helps regulate the opening and closing of the stomata, the openings or pores on the underside of leaves by which oxygen and carbon dioxide are exchanged with the atmosphere, and the loss of water vapour through transpiration is controlled. It Increases root growth which increases nutrient uptake and improves drought resistance, and also increases resistance to frost, insects and diseases. Optimum levels of potassium levels produce uniform ripening and growth rate of fruit, as well as better food quality, flavour and grade.

Agricultural extension agencies advise that large amounts of potash are needed by most plants, and that a deficiency of potassium or inadequate amounts of the macronutrient lead to stunted plant growth and reduced yields, and that potassium levels affect not only  yield, but fruit size, juice quality and shelf life.

Since potassium plays such a key role with water regulation, a deficiency would clearly increase the stresses associated with fruit drop discussed in the previous section.

Solution: Ensure that citrus trees are fertilised with a balanced fertiliser as previously discussed. Additional potassium can be supplied by using seaweed extract (which is not fertiliser but contains a good amount of potassium), wood ashes (used in tiny quantities only as it’s very alkaline), or sulphate of potash (potassium sulphate) – all these are certified as acceptable in an organic garden.

Don’t ever use potassium chloride as it can be toxic to plants, it’s the cheap nasty alternative that fertiliser manufacturers substitute to save money!

Even if there are sufficient potassium levels in the soil, they may not be accessible to plants, unless we make certain improvements.

How to Improve Plant Uptake of Potassium

There are several factors that can affect potassium uptake by plants:

  • soil moisture
  • soil aeration and oxygen levels
  • soil temperature

Higher soil moisture levels increase potassium availability to plants by enhancing the movement of potassium to plant roots.

As soils get wetter and closer to saturation, where they become waterlogged, potassium uptake decreases, because air is excluded from wet soils and oxygen levels become very low. Air is necessary for both root respiration and potassium uptake.

All plant physiological activity, including root activity, increase as soil temperature increases, leading to increased potassium uptake, with the optimum soil temperatures being between 16-27°C (60-80°F)

Solution: Water enough but don’t overwater, and mulch the soil in late spring to keep the soil temperatures in the optimum range during very hot weather and to reduce water loss to evaporation.

Other Factors Causing Fruit Drop

Sometimes there may be several factors causing increased fruit drop in citrus. How does the fruit drop mechanism work in fruit trees?

Fruit drop (also known as fruit abscission) is regulated by the balance of two endogenous (meaning from within) plant hormones, auxin and ethylene. When the ratio of ethylene to auxin is higher, it induces the enzymes which dissolve cell wall components in the abscission zone between the fruit and stem (peduncle) at the button, which separates the fruit from the tree.

Ethylene is produced in response to stress factors such as water stress, physical injuries, frost damage, and decay of the fruit. When the fruit is injured, ethylene gas production is triggered, which may cause fruit to drop.

If citrus trees are planted in poorly drained soil, extended hot, rainy weather in late late summer to early autumn may lead to root root and cause excessive fruit drop in mature trees

Additionally, if the lower branches of the tree canopy are shaded out and don’t receive adequate light, the fruit is quite likely to be shed from those branches. Prune citrus to an open vase shape to ensure good light penetration through the canopy, which is important for even fruit ripening.

Other articles on citrus problems and how to fix them:


  • University of Arizona Cooperative Extension – Diagnosing Home Citrus Problems, AZ1492 April 2009 – John Begeman, Glenn Wright
  • University of Georgia Extension – Citrus Fruit for Southern and Coastal Georgia, Bulletin 804, 20154 – Gerard W. Krewer, Bob Westerfield
  • LSU AgCenter – Citrus Problems, 3/21/2015 – Daniel Gill 
  • University of Florida Institute of Food and Agricultural Sciences (IFAS) Extension – Citrus Problems in the Home Landscape, Publication #HS876 – Mongi Zekri and Robert E. Rouse
  • University of Florida Institute of Food and Agricultural Sciences (IFAS) Extension – Citrus Nutrition Management Practices, HS1292 – J. D. Burrow, T. Vashisth, M. Zekri, S. H. Futch, and A. Schumann
  • Virginia Cooperative Extension – VCE Publications / 426 / 426-613, Environmental Horticulture: Guide to Nutrient Management – Diane Relf, Extension Specialist, Horticulture, Virginia Tech
  • University of Minnesota Extension – Potassium for crop production
  • New South Wales Department of Primary Industries – Growing lemons in Australia- a production manual
  • Potassium Nutrition in Plants, Fact Sheet. A&L Canada Laboratories Inc.

16 thoughts on “Citrus Problems, Why Citrus Fruit Drops and Flowers Fail to Develop

    1. I agree with you, Potassium is amazing. I started using potassium on my citrus and Peper plants, what a difference it made this season. The problem I have is I’m not sure when to use it. Does one use it at the start of spring, once, or does one use it during the growing season? I’m not sure how much potassium sulphate or nitrate to use per liter of water and how often.

      1. Hi Paul, use potassium sulphate, and apply either once at the start of spring which is usually sufficient if you don’t have sandy soils, or a few weeks apart during the growing season.

        The application rate for potassium sulphate is explained in detail in this article subsection: How to Correct Plant Potassium Deficiency –

        Don’t use potassium nitrate, the nitrates fertilisers are used as a source of nitrogen, and will push out lots more new green growth instead of flowering and fruiting growth.

  1. My citrus is not flowering and the other is dropping all fruits. What could be the problem? Two of my other trees died. What am I doing wrong?

  2. Great article….i am getting a recurring problem….i have a hickson mandarin in sandy soil…..i have an imperial mandarin in a 50 litre pot…..both have grown a reasonable crop of fruit each year and the size gets good but just as they start to go orange…..they drop off one by one….they get fed in winter with compost and slow release ferts..watered twice a week through our hot dry summers….Dont know what i am doing wrong……do they need postassium when the fruits are maturing please?…i was told not to feed them when the fruits were ripening… i really dont know now ! …hope you can help….cheers Jon

    1. Hi Jonathan, potassium is required for flower and fruit retention, it’s water soluble and can easily leach out of soils. Potassium is more prone to leaching in sandy soils and in pots. Add lots of compost around the tree and cover the compost with mulch. Soil organic matter helps retain nutrients. You could also add some zeolite to increase moisture and nutrient retention. Don’t dig it in as citrus have very shallow roots near the surface of the soil.

      The reason why we don’t add nitrogen fertiliser when citrus trees are fruiting is that we don’t want to force new leafy green growth at the expense of the fruit. You can add potassium on its own in the form of potassium sulphate (sulphate of potash), or use a seaweed extract that contains potassium (check the label). With appropriate soil amendment and additional potassium, your trees will retain their fruit and ripen them!

  3. My problem is as follows:

    The oranges on the orange tree attract rats, the oranges are also VERY bitter, I do not wish to get rid of the orange tree, but I do NOT want it to bare fruit, so my objective is to STOP IT from fruiting.

    I have been told if I spray the orange blossom flowers when they open with horticultural oil this will stop the fruit from setting & they will fall off the tree before they ever get a chance to mature into fully developed oranges

    I would be grateful if you could recommend any oil based products that I could mix up & use as a HOSE-ON-SPRAY??? (rather than a regular spray, as the the orange tree is 3 metres tall & I can’t reach it with a regular spray)

    Or any other methods I could implement to cause blossom flower bud drop???

    1. Update; the orange tree is covered in what seems like thousands of orange blossom buds 🙁 so I am spraying it with diluted richgro urea, by putting it in an old empty yates hose-on pack/bottle & diluting it with urine, in a hope that the high nitrogen will cause bud/blossom drop.

      PLEASE advise what else I can do further???

      At the current time of writing I have not sprayed the orange tree buds/blossom with horticultural oil as the majority of the buds have not opened

      1. Spraying urea will just fuel more leafy green growth, which will make your tree grow larger, and unnaturally so, because urea is pure nitrogen, it has a NPK ratio of 46:0:0 which is ridiculously high, manures are about 3 or 4 in their nitrogen ratio! The soft, sappy growth will attract lots of aphids!

        If you really want to keep the tree, I’d recommend pruning it down to size and then summer pruning the new growth down to half to prevent it fruiting too much, as citrus fruit on young new growth. manually remove the little fruit that’s left if you don’t want it. That would be the easiest way to do it! It’s either a big tree with fruit, or a small tree with little fruit that is easily removed, those are the real-world choices. Hope that helps! 🙂

    2. Hi Jo, you’ve created the unsolvable problem for yourself here!

      First, are the oranges bitter, like grapefruit, or are the sour, in which case they might be Seville oranges, in which case they’re valuable.

      If the citrus is very thorny with bumpy looking fruit, you might just have the rootstock which has grown into a tree, which case is only good for grafting onto.

      Horticultural oil will clog up some of the flowers to prevent pollination, but won’t work 100%.

      By trying to prevent a large citrus tree from flowering and turning it into some sort of non-flowering hedge, you’ve set up an impossible task for yourself.

      Why does it have to be so big?
      If you prune off the ends of the branches where the flowers and fruit form, it wont fruit.
      If it was planted in a shady spot with less sunlight, it won’t fruit.

      There’s nothing safe that can be sprayed to induce bud drop unfortunately! 🙁

Leave a Reply