Number of Plants Blooming By Month in the San Gabriel Mountains in 1999

We have long wondered how the blooms vary by season. There are many possible ways to define this, but one natural and simple way is to use the 1999 Bloom Identification Guide, giving a month-by-month record of when plants bloomed in the SGM.

We have counted the number of plants listed as blooming in a given month in the following way:

There are 137 plants listed in our 1999 Bloom ID Guide, each observed throughout the year. A breakdown of the number by color is given below (see also a histogram). To avoid dealing with colors with small numbers, we have combined the colors as we have on the individual bloom ID pages, given in the second number column below.

ColorNumber (each color)Number (combined similar colors)
white43 43
cream6 43
pink9 24
yellow-green1 27

The number of blooms per month by color shows the surprising result that the number of blooms in 1999 actually peaked in June and July, not in the spring!

The most frequently encountered bloom color does change with time in the following sequence:

MonthDominant Colors
January - FebruaryYellow
MarchYellow and Blue
April - MayBlue
June - JulyWhite and Red
August - SeptemberRed

A plot of the percentage of a given color blooming per month shows that:

Thus, for example, the dominance of yellow blooms in January and February results from yellow flowers having the most uniform distribution over the year, and not because most of the yellow flowers bloom at that time. You are more likely to see a yellow bloom later, from March to July, but you won't notice the yellow as much due to the other colors present then. In January and February, you won't encounter very many blooms, but those you do encounter are more likely to be yellow than any other color.

These results of course combine observations for all altitudes, and hence observations at a given altitude will probably not follow these composite curves. See 1999 bloom observations by date and altitude.

Also, these results may not correlate well with the maximum bloom as measured by the eye, since some blooms are significantly showier than others. For example, few plants are so stunning as fields of purple lupine (April - July) or blue California Lilac (March - May). However, it certainly measures the number of different species blooming at a given time, and it happens that those particular plants match the peak bloom periods deduced for the color category as a whole.

Now, of course, the question is how representative the year 1999 was. Stay tuned - we'll update this page with later years as they become available!

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Copyright © 2000-2001 by Tom Chester and Jane Strong.
Permission is freely granted to reproduce any or all of this page as long as credit is given to us at this source:
Comments and feedback: Tom Chester | Jane Strong
Updated 5 August 2001