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Citrus trees, beloved and bewildering

That little orange is doomed -- sustenance has been cut off by the tree and it
will fall off soon. It's "June drop" time. (Photos: Kathy Morrison)

Home garden favorites have a range of quirks

Question: How is an orange tree like a pet cat?

Answer: You love it, even though you don't understand it most of the time.

Really, every lemon, orange, lime, grapefruit and mandarin sold to backyard gardeners should come with an instruction booklet -- or, more realistically these days, a YouTube mini course.

Right now, orange tree owners are flummoxed by a regular occurrence: the "June drop" of excess tiny fruit.

"Aw, gee, look at all these oranges falling off! Must be something wrong. Or maybe it's the weather."

Nope. It's normal. The tree is self-selecting how many oranges it can grow this year. It'll drop as much as 95 percent of the blossoms and fruit it had in spring.

With thanks to UCCE master gardener Bill Krycia, whose citrus class I took in April, here are five more fascinating, flummoxing facts about citrus trees:

1) Commercially sold citrus trees in the U.S. are grafted onto rootstock for hardiness and better production. But the rootstock can and will take over the tree if you let it. Example of the reaction when this happens: "My lemon tree was great for years but now it's producing these bumpy thick-skinned lemons." A significant part of the tree probably died back for some reason -- frost, maybe -- and suckers from the rootstock have taken over. The weird fruit is from the rootstock.

(P.S. The rootstock used for dwarf citrus is called Flying Dragon. I love that name.)

Can't thank the bees for these beautiful navels-to-be,
on the same tree as the one above. Navel oranges
do not depend on pollinators to set fruit.
2) Bees do not pollinate navel oranges. Navel oranges are parthenocarpic (Satsumas, too), meaning they set fruit without pollination or fertilization. All those early blossoms are merely floral -- fun for bees! The later blossoms produced by the tree are the ones that turn into oranges. Seedless oranges, of course. Yes, weird.

3) Citrus trees are evergreen -- they don't drop all their leaves in fall, like apple or pear trees  -- and the leaves are multi-taskers. They make food for the tree via photosynthesis, of course, but their additional role is storage. Along with the twigs, branches and roots, the leaves also store excess food (aka photosynthate) through winter. These storage sites are most packed in late winter and early spring, just before spring bloom. This is why citrus shouldn't be pruned then: The fruit yield will be much lower.

4) Citrus varieties easily cross, and the origin of certain varieties is not certain. But this also means new hybrids are being created all the time, especially at UC Riverside, a hotbed of citrus research. The red-fleshed "Valentine" pummelo, for example, is the result of a UCR cross of a pummelo, a blood orange and a mandarin.

5) Some citrus trees, especially mandarins, produce in two-year cycles, with a heavy crop one year, followed by a lighter one. Pruning the tree during the summer before the heavy crop ripens actually can even out this cycle, but who's willing to sacrifice that crop? I know, I know, but do prune if the tree is overburdened and the limbs could break.


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Garden Checklist for week of April 14

It's still not warm enough to transplant tomatoes directly in the ground, but we’re getting there.

* April is the last chance to plant citrus trees such as dwarf orange, lemon and kumquat. These trees also look good in landscaping and provide fresh fruit in winter.

* Smell orange blossoms? Feed citrus trees with a low dose of balanced fertilizer (such as 10-10-10) during bloom to help set fruit. Keep an eye out for ants.

* Apply slow-release fertilizer to the lawn.

* Thoroughly clean debris from the bottom of outdoor ponds or fountains.

* Spring brings a flush of rapid growth, and that means your garden needs nutrients. Fertilize shrubs and trees with a slow-release fertilizer. Or mulch with a 1-inch layer of compost.

* Azaleas and camellias looking a little yellow? If leaves are turning yellow between the veins, give them a boost with chelated iron.

* Trim dead flowers but not leaves from spring-flowering bulbs such as daffodils and tulips. Those leaves gather energy to create next year's flowers. Also, give the bulbs a fertilizer boost after bloom.

* Pinch chrysanthemums back to 12 inches for fall flowers. Cut old stems to the ground.

* Mulch around plants to conserve moisture and control weeds.

* From seed, plant beans, beets, cantaloupes, carrots, corn, cucumbers, melons, radishes and squash.

* Plant onion sets.

* In the flower garden, plant seeds for asters, cosmos, celosia, marigolds, salvia, sunflowers and zinnias.

* Transplant petunias, zinnias, geraniums and other summer bloomers.

* Plant perennials and dahlia tubers for summer bloom.

* Mid to late April is about the last chance to plant summer bulbs, such as gladiolus and tuberous begonias.

* Transplant lettuce seedlings. Choose varieties that mature quickly such as loose leaf.

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