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If your lilac bush isn’t blooming properly, there’s only one likely culprit

  • Author: Jeff Lowenfels
    | Alaska gardening
  • Updated: July 9
  • Published July 9

I hate to be repetitive, but I guess this is the nature of a garden column that centers on what you should be doing from week to week and spans some years. New readers arrive and ask the questions that are asked every year. I can’t ignore these, but I can abbreviate answers so as not to bother too many loyal readers.

First, those dead blotches on your lilac leaves are caused by moth larvae, Caloptilia syringella: tiny, quarter-inch-long caterpillars. They appeared in epic numbers last summer. They mine tissue between leaf covers and get all comfy inside. Next, they use a “silk” thread to roll up leaves while they continue eating them. They pupate over the winter.

Many lilac bushes in Southcentral Alaska are showing brown spots on their leaves this year (Photo by Jeff Lowenfels)

If the problem proves to be as bad as it was last year, perhaps next spring, as lilacs leaf out, we might consider doing something organic to try and control things.

Hopefully, however, natural predator populations will adjust to deal with the problem. Don’t spray and don’t fret.

Once you see them, the damage is done and spraying not only won’t help, it will harm those predators.

While on lilacs, why didn’t yours flower? After many years of this question, I can almost promise you it is because a moose, or more, ate the flower buds during last fall or winter, leaving your plants barren.

I know. I know. How can this be, when some plants on the property are in full bloom? Trust me on this. It is also the reason your lilacs may only bloom on top of the shrub, where the buds were above winter’s moose “reach line.”

Next, the appearance of the spittle on plants, which is alarming so many, is caused by a tiny insect that pumps air and water out of its abdomen. It is a neat trick designed, probably, to keep the bug moist and safe. They are harmless, far and few between and do not need any eradication, as if there was one!

OK: lots of tomato flowers, but no fruits? This is probably caused by one or both of two problems. The first are too-cool temperatures at night. Shut the greenhouse door at night to keep it above 55 degrees so the flowers don’t fall off.

Second, indoor greenhouses may lack the insects and air currents necessary for pollination. Add a small fan. Or you be the insect. Use a small paint brush or Q-tip and move from flower to flower. Touching an electric toothbrush to limbs to make them vibrate, imitating the bumblebee you are missing and works as well.

What about only getting male squash flowers? This happens at the start of the season. It is early, yet. Female flowers will appear soon, and you will be glad the males are there to provide pollen.

Next, is there a way to keep the neighbor’s cat out of your garden? Grrrr! Don’t get me going, again, on this issue (and send me email, as I won’t read it). Do we need a hunting season on feral cats? They are everywhere and they are killing tons of birds. The rest of Alaska’s cats, of course, are safe and sound in their respectful, good citizen owners’ homes.

You can trap cats humanly. And you can try the old motion-activated sprinkler to scare them off. Look these gadgets up on the web. You will find some are sold locally.

Ah, I knew it was coming: What is that purple flowering vine that is all over the place? It is Vicia cracca, aka “bird vetch”, a legume. introduced to Alaska at Ramparts in 1909. It fixes natural from the air so it can be utilized by plants. It is now all over Alaska.

To control vetch, mow it down during the season so it doesn’t produce flowers and then seeds. This won’t kill the plant, because it spreads by underground rhizomes as well as seeds, but it will control it. A weed eater works great.

It is tempting to spray a 2-4-d-based herbicide on vetch. Please don’t. Real gardeners and Alaska yardeners do not spray toxics. I know I said I hate to be repetitive. Still, I repeat myself on spraying again and again.

We gardeners have simply become too accustomed to reaching for applicators of premixed herbicides and pesticides to make our lives easier. Please don’t. Love thy neighbor and family over your lawn or gardens. I will keep repeating that.

Jeff’s Alaska garden calendar for the week

What’s in bloom? The Alaska Botanical Garden is open and the website has a listing of what is in bloom. Lots more on and at the garden.

Radish: Do you need to harvest and plant more? Don’t let it get too pulpy.

Snap peas: Should be producing. Harvest when young for the best taste. The plants will continue to flower and produce all summer.

Clover: I like it and want to encourage it, so I am letting ours flower and go to seed.

Watering: 1-2 inches or so between you and mother nature per week for the lawns, trees and shrubs. A traveling sprinkler and water timer really are musts.

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