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Question of the Week © 2017 Mike McGrath

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When Forsythia Becomes a Ground Cover

Q. I currently have a forsythia that is growing along the ground. I heavily pruned it after flowering last year (after letting it grow out of control for years). Is there something I should do to control it now? Or just leave it be?

----Jason in Kettering, Ohio

A. This topic always reminds me of the time I famously tried—and failed—to kill a forsythia. There were three huge shrubs in front of our house when we moved in. They bloom magnificently in the Spring; an amazing burst of bright yellow. But I needed to plant some other things out there and tried to dig the center one up. I finally had to host a 'forsythia removal party'; it took eight guys to pull the enormous root ball out of the ground. It then lay there on its side for a week until I could 'convince'—the prefix of which is 'con'—a different bunch of guys to come over; and we finally muscled it into the woods.

…Where it continues to bloom every Spring some twenty years later. On its side.

Yes, forsythia is 'easy to grow'; a phrase that has many meanings. But the survival of my specimen is a clue to what's going on with Jason's plants in Kettering: "layering". Some plants can be propagated simply by pressing one of their branches down against the soil. Sometimes you need to put a rock on top to keep the soil contact, but with forsythia—and tomatoes—a branch that droops down low enough will do this naturally.

Tomatoes?!

Absolutely. If you grow a big vining 'indeterminate' variety without proper support, any part that touches the soil will send down roots. Some gardeners in long season climates will deliberately put out plants without support, wait a week, sever the rooted portions and move them to different locations as new plants. It's also a good way to salvage a damaged plant early in the season.

At any rate, my 'Lazarus Plant' isn't unique; a lot of forsythia grow sideways. Now: Is this related to the reported heavy pruning? (Which was performed at the correct time of year—right after blooming.) Or did Jason just reduce the height enough to notice all the lateral growth for the first time? My shrubs often send up aerial shoots that are fifteen feet tall, which pulls your eyes up high. But I've learned to also look down; and so I'm always pulling out 'crawlers' in between the plants.

…Which makes this shrub sound like running bamboo; which, BTW, is being outlawed in many communities because its invasiveness can undermine the structural integrity of neighboring buildings and roadways. But I can't put forsythia in that rogue's gallery. It isn't hard to control—my 'layered' plants pull up easily from wet soil. And more importantly, the spectacular spring display forsythia puts on attracts a slew of beneficial insects. For three big reasons…

1) The number of individual flowers on a mature plant can almost be beyond comprehension.
2) Those individual flowers are smallish, and small flowers attract the greatest diversity of pollinators and beneficials.
3) And early Spring bloomers like forsythia are crucial to the long-term survival of native bees—insects that both pollinate our food crops—and many of the beneficial insects that prey on pests. But, as they say on TV, there's more.

A free ShamWow with every shrub! ("Just pay a separate handling fee!" )

Seriously, forsythia flowers are yellow; that's THE favorite color of hundreds of species of native bees; non-stinging, solitary nesting creatures of all shapes and sizes that don't make honey but do provide pollination for many of our fruits and flowers. But that's not all!

"We'll double your order!"

No, but we will cut in half the number of grubs in your soil—before they can emerge as plant-destroying Japanese beetles, June beetles, rose chafers and other destructive members of the scarab beetle family. Forsythia is one of the plants that produce what are called 'extra-floral nectaries'; glands not involved with pollination that pump out massive amounts of sugar.

One of the insects most attracted to this forsythia sugar is a predator known as the Spring Tiphia Wasp. It gets an energy boost from the sugar water and then hovers over the nearby soil, listening for the distinctive vibrations of awakening grubs. Then she—it's always the females who do the hard work—burrows down into the soil, stings and paralyses the grub and lays an egg on it whose occupant will feed off the dying grub.

That baby predator will then spend the summer, fall and winter underground and emerge as an adult wasp the following Spring to sugar up on forsythia blooms and then attack that year's grubs. And these insects are super-effective. In a study performed in Connecticut*, 61% of Japanese beetle grubs had been "impacted" by the wasp. That works out to half as many beetles ravaging your roses!

* http://ipm.uconn.edu/documents/raw2/The%20spring%20Tiphia%20a%20natural%20enemy%20of%20the%20Japanese%20beetle/The%20spring%20Tiphia%20a%20natural%20enemy%20of%20the%20Japanese%20beetle.php?aid=167

Another good article:
http://drmcbug.com/parasitic.htm


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