Fall in the high country or temperate climates bursts upon the landscape with a riot of dramatic color changes. Fall in the low desert creeps in showing only subtle changes in plants.

The former is easily recognised the latter takes a sharper eye.

Plants growing in temperate climates respond quickly to the weather. Short days and chilly nights quickly trigger the trees into cycling their leaves' energy into the trunk and root tissue. The leaves then lose chorophyll and the green color leaving the color of the minerals remaining in the leaf. Thus we see the yellows, reds and purples showing through after the chorophyll leaves.

For most plants fall glides slowly into our mild winters and plants respond to the gentlness slowly.

The low desert offers the only short days and some relief from the heat. Plants, like humans find the relief from heat a welcome part it.

Plants respond by sighing collectively and starting a second flush of growth. This new growth often looks nturient deficient. It either looks yellowish or shows the classic iron defeciency symptoms of yellow leaves with green veins on new growth.

As explanation for the wymptoms we must remember that half the plant is underground. The air temperatures might be glorious for plant growth but the soils have quietly cooled underfoot without our noticing. Roots simply have a harder time absorbing the nutrients when the soils are cool.

If your plants exhibit iron deficient symptoms you can add an iron fertilizer to the soil and in two weeks they will green up. Or you can forget the iron application and in a fortnight the plants will green up. Its a matter of cool soils less than a lack of iron.

For the last month and until late March the days are shorter than nights. This daylength stimulus causes most plants to reduce their leaf load. Even evergreen plants begin a systematic dropping of older leaves. Hibiscus, citrus, silk oaks, bottle trees, pines etc. all drop at least some of their older foliage this time of year. Deciduous trees drop thier leaves in December.

Even some houseplants respond to daylength and drop older leaves. Its the daylength that triggers it and does not mean they are getting sich or need fertilizating.

Even though most plants growing in this climate offer little of the dramatic fall color, one native desert plant offers a nice leaf color display in October. In fact they are in full regale now out in the desert especially if viewed with when the sun is low. If you've seen it you know; if you've not seen it you should go.

I won't say the name of the plant. I will only give the clue that the first two letters of its name are the same first two letters of this month. Get out and seethe display soon before all the leaves drop.

Written by Terry Mikel, College of Agriculture and Life Sciences, the University of Arizona, 602-470-8086.
Material originally appeared in Arizona Republic
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