Keeping Asters Green

I am not a high-maintenance gardener, so sometimes when my plants just look great on their own I am thrilled.  I plant things that don’t need a lot of babying with few exceptions. An exception, though, is Asters.  They epitomize fall and add too much lighthearted warmth to the garden to just give up on them.

This fall, some of my Asters have surprised me with their health.

Asters, Sedum, “Autumn Joy“ and Japanese Anemone

Asters require two main types of maintenance.  The first is that you should pinch them back a couple of times prior to the first week of July, to make them bushy and encourage heavier flowering (and to delay flowering if you wish).  The second type relates to Rust and mildew, and that’s what this post is about.

Rust and mildew occur mainly in humid summer conditions, like those in Southern Ontario.  My relatives on Vancouver Island do not have this problem with Asters and Phlox due to their dry summer air.   This difference forces them to water constantly, and even that kind of watering does not bring about this diseased condition, since their climate dries the plants as soon as they are done.

Mildew and rust developing in Summer Phlox

Mildew and rust developing in Summer Phlox.  Note white splotches on remaining lower leaves.

The result of mildew and Rust is that the leaves and stems will begin to turn brownish and crumbly from the ground up, in late summer.  This will work its way up the stems, which will look anaemic and become bare so that by the time your poor flowers bloom, the plant itself can be scarcely worth looking at.

You’d think you could just tuck them behind another plant so that only their flowers show, but this prevents air circulation and makes it worse.  Also, some of the cutest Asters are low and would make a nice edging for your borders, if only they could stay healthy.

Here are the four best ways to combat this plague:

1.     Plant susceptible plants where air circulation is good, in a fairly open place, rather than tucking them into still corners or closing them in with too much other foliage.

2.     Water early in the day if necessary, deeply and infrequently, giving the plants the rest of the day to dry off.

3.     From mid-summer or once the humid period really sets in, spray the plants with an organic fungicide or other product designed for this purpose.  You usually have to re-spray after a heavy rain and with a certain frequency, soaking the plants with it–follow the package directions, of course.  This is where I tend to fail my Asters and Phlox, I will admit.

4.     Clean up whatever fallen pieces you can, and remove cuttings of mildewed or Rust-infested plants right out of your garden.  Do not compost them either.  At least, this way, you minimize the spores that remain in your garden to affect subsequent growth.

Asters and Grasses are a good fall combination–these ones don`t have quite enough air circulation

Other plants that are susceptible to this nuisance are Monarda, Bee Balm; Phlox; Alcea Rosea, Hollyhock; and most Roses.  Now, West Coast gardeners, I am sure you are glad you don’t have to bother with all of this!Asters



Good luck enjoying these starry fall beauties.


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About patinaandcompany

I am a compulsive beautifier of all things habitable. Give me your ugly, non-functional and visually repellent, and I am in my element. Also, an avid and experienced gardener determined to share my horticultural experiences with others. See more at "About"
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4 Responses to Keeping Asters Green

  1. Pingback: Bittersweet October | patinaandcompany

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