Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
4/9/01
Contacts:
Mark Gleason, Extension Plant Pathology, (515) 294-0579,
mgleason@iastate.edu
Elaine Edwards, Continuing Education and Communication
Services, (515) 294-5168, eedwards@iastate.edu
Yard and Garden Column for the Week Beginning April 13, 2001
Garden Clean-Up -- It's Not Too Late
By Mark Gleason
Extension Plant Pathologist
Iowa State University Extension
The snowdrifts have finally passed into memory, except in northernmost Iowa. All of a sudden, green shoots are poking impatiently through last year's crust of dry, flattened plant debris. Now is the right time for a thorough spring cleaning -- of your garden.
Why bother picking up the leftovers from last season's garden? Wouldn't it be more "natural" to let everything decay in place?
"Natural" may not always be best, though. Here's the problem. The plant debris from your 2000 garden is protecting disease fungi that are waiting patiently to bring your plants down in 2001. If you don't want to get caught with your plants down, cleanup is a must.
Some plants in your garden need cleanup worse than others. Let's start with peony, the traditional star perennial of Iowa gardens. You may have noticed large, purple-brown spots on your peony leaves last year. The problem, called leaf blotch, is caused by several species of fungi.
These fungi lurk all winter in the dried peony leaves that collapse in a circle around the plant. If we have a wet spring -- as some meteorologists are now predicting -- these furtive fungi will wake up, start multiplying and pounce on the newly emerging leaves. This nightmare scenario means brown, withered leaves by the time flowers appear at the end of May. The combination of fresh flowers and dead leaves is not what you are seeking from peonies.
To delay peony leaf blotch, or even prevent it entirely, cleanup is essential. Within the next week or so, clip off the old stems at the soil line and rake them clear of the peony bed. This simple step removes almost all of the surviving fungi, so they can't overwhelm the new shoots.
Irises also appreciate a cleanup. Many varieties of German, or bearded, iris fall prey to iris leaf spot, a fungal disease that produces rounded, wet-looking, brown spots on leaves and eventually turns the entire leaf brown. Wet weather and no cleanup equals sick leaves when the irises bloom.
Cleaning up an iris bed calls for a pair of stout shears or scissors. Clip off the old leaves at the base and rake them out of the bed. In fact, German irises are better off surrounded by bare soil than dead leaves. The reason is that the moth that gives birth to the iris borer likes to lay its eggs in dead leaves.
The iris borer is a fat, shiny larva that tunnels from the leaves into the corms, accompanied by stinking, slimy decay bacteria that rot the corm. Encountering these larvae and their bacterial cronies is among gardening's most disgusting moments. If you would rather avoid this trauma, cleanup is definitely the way to go.
Once you've tackled the peonies and irises, don't forget the roses. Black spot, the bane of rose growers in Iowa and elsewhere, is a fungal disease that causes, yes, black spots on the leaves, and often defoliation, too. Hauling out last year's dead leaves will slow down black spot in 2001. Take care to avoid excessive blood loss from thorns during the cleanup process. But highly susceptible roses, such as hybrid teas, will need more help -- probably in the form of regular fungicide sprays -- to stay healthy-looking all season.
In the vegetable garden, the mantra is "rotation." And for good reason, since shifting particular types of plants -- tomatoes, for instance -- to different parts of the garden each year effectively suppresses their common diseases.
But many home vegetable gardens are too small to allow much in the way of rotation. Whether you rotate crops or not, it's helpful to uproot all the dead plants from the 2000 garden, rake the soil surface clean of all plant debris and then roto-till or spade the soil. This final step speeds the decay of whatever bits of last year's plants still remain.
In a perfect world, all of this virtuous cleanup would take place in the fall, soon after growth stops in late September or October. Since we don't live in that world, we can still reap most cleanup benefits by catching up now.
What should you do with all that contaminated plant debris? How about dumping it in your compost pile? If your pile is like mine, don't do it. Most so-called compost piles are actually mere heaps of organic debris. Without layers of fertilizer and soil, and repeated watering and turning, organic debris piles won't develop the heat needed to kill off the bad fungi and bacteria.
Like fall cleanup, true compost piles exist mostly in the imagination or in extension bulletins. In the real world, it's prudent to burn (if legal where you live), bury or dispose of disease-infested garden leftovers. Even though I hate to throw away yard waste, I make an exception when it comes to contaminated debris.
Spring cleaning is cheap, low-tech, effective, provides beneficial exercise and involves no genetically modified organisms. Your garden will thank you for it.
ml: isugarden
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