Garden Training for Excess Raining

I thought I had a handle on just how wet the summer has been. My rain gauge (that measures 100ths of an inch, I'm proud to say) recorded 9.30" for June. I just spoke with a fellow horticulturist who was telling me that she was pruning and found gangs of slugs hiding in yew branches four feet off the ground. We've revealed a new definition of saturation point: So wet that even slugs seek higher ground!

Short of dragging water-soaked containers under overhangs or setting up umbrellas over drought-tolerant perennials, there's only so much a person can do to stem the flood waters. Here are a few proactive things that may help save plants after the recent deluges.

Override the Sprinkler System 
Congrats to those folks that have automatic overrides. For those that have manual controls, please consider shutting off your system on an as-needed basis! We've all seen sprinklers gushing water in the middle of a downpour. In addition to the ecological benefits of conserving water, think about the dollar savings.

Drain Your Saucers
Plants in containers (with holes in the bottom) have much better drainage than plants in our clay-laden garden soils. Hanging baskets or decorative pots with saucers (attached or otherwise) must be checked daily and emptied. The potting mix will have absorbed all the moisture it can hold after 30 minutes. After that, roots are dying. So, be extra vigilant about water removal with all the rain we've been receiving.

Formerly full begonias

Remember to Fertilize
Nutrient deficiencies may start showing up in plants on a patio near you, namely yours. Most potting mixes are "soilless". They are either coarse peat or bark-based to promote drainage. They have minimal nutrient content regardless of whether the bag says "Fertilizer Added" or not. Constant rainfall, like our own frequent watering, leaches nitrogen out of the bottom of the pot. Nitrogen is responsible for leaf and stem growth, as well as leaf color. Add a complete fertilizer (nitrogen, phosphorous and potash-containing) to keep your plants in tip-top shape as needed.  

Control the Slugs
Populations of slugs and earwigs are exploding. Protect hostas, lettuce, spinach and other slug faves with the iron phosphate baits. They are applied directly to the ground under and around your ornamentals and vegetables. The varmints eat the bait and crawl away to die within a day or two.

Chewed on petunia

Check New Plantings Daily
Newly planted perennials, shrubs and trees that were container grown will need to be checked daily for water. Remember they've been potted in a coarse mix to promote drainage. That doesn't change because they're out of the pot and in the ground. It is possible that the day after a good rain the root ball of your new plant could be dry, even while the surrounding soil is wet. Never assume anything about rainfall and new plants.  

Check Before Watering
Wilting plants MAY or MAY NOT indicate a need for water. Ironically, plants wilt when they're standing in water just the same as if they're bone dry. So, before you water that wilting Hydrangea or coleus in the midday sun, check the mulch or soil surface to see if it's moist. If so, wait a few hours and revisit the plant in the cooler part of the day, and see if it hasn't returned to normal. If not, water may be needed.

Water stress-induced leaf roll on tomato

Preventative Treatments
Use fungicides preventatively on plants with a past history of fungal issues. Roses and black spot, tomatoes and blight(s), Garden phlox and powdery mildew, are among the common health issues to be expected with constant rainfall and high humidity. Again, prevention of further infection is the goal. Present symptoms will not be reversed.

Enjoy the lush growth in your garden because of, and in spite of, the incredible rainfall!!!

Rain sodden, down-trodden gardens

When the surface water is an inch deep for a full day in my delta “garden” I know the soil is saturated. (If you saw it, you would understand why garden is in quotes).  While my dwarf River Birch (Betula nigra ‘Fox Valley’) loves periodic flooding, few plants do. Landscape plants recovering from 2012’s  historic heat and drought  needed rain- no doubt. But the extreme flipflop to saturated soils is equally dangerous.

What are the immediate symptoms of too much water? 

Surprisingly, plants may wilt even though the mulch or soil surface is wet. Roots need oxygen to transport  water so they wilt in saturated soils.

Nitrogen (responsible for leaf color, vigorous growth) is highly mobile in soil and may be leached by heavy rain. Nitrogen deficient leaves will be pale throughout, including veins. New leaves of water-stressed plants  may be smaller than normal. Older leaves will show yellow first. It’s possible that even lawns may start looking lighter-than-normal green.   

Water-induced nutrient deficiency 

Unusual colors that might  otherwise be interesting may start showing at the edges or throughout the leaves between the veins. Yews, a landscape staple, are poster plants for wet soil damage. Their needles turn rusty-orange – all the way to the branch tips. Also, keep your eyes peeled for black, purple or discolored bands (cankered) stems on deciduous trees and shrubs.

Is there a difference between wet and flooded?

Absolutely. Areas that often have standing surface water for a day or more require  flood tolerant plants (or a great landscape firm to change the drainage!). For example, trees such as Bald Cypress, Swamp White Oak and River Birch (have you seen the cool dwarf cultivars like ‘Fox Valley’?) are perfectly happy with periodic flooding. While it seems logical please understand plants are not Wet-Dry vacs that will pump an area dry. Select flood-tolerant plants for these sites. 

'Fox Valley' River Birch

What about containers?  

Plants in containers with holes in the bottom drain better than plants in the ground. Most potting mixes are “soilless”, being coarse peat or bark-based, to promote drainage. The downside is minimal nutrient value. So, be sure to fertilize throughout the season (more frequently in sun, less for plants in shade) in years with heavy rain. Be sure that containers with saucers (attached or otherwise) are emptied religiously. After 30 minutes the soil will have absorbed all the moisture it can hold. After that, roots die.                                        

What about insects and disease?

Pestilence is most certainly in our immediate garden future. The jury is out on how this moisture will affect Japanese beetles. Slugs should be rampant. Protect hostas, annuals and other perennials whose foliage  rests on the ground. Earth-friendly baits, like Sluggo, contain iron phosphate and are safe even around edibles. Slugs eat the bait, get a tummy ache and crawl away to die in a few days. It’s alright. Chances are, you’ll never run across the proverbial slug graveyard.

Fungal diseases will abound. The usual suspects, black spot on roses, tomato blights, powdery mildew and a jillion leaf spots are a sure bet as we move into heat and humidity. Remember, fungicides must be applied ahead of the infection. They will not reverse symptoms that are already present.

Can I forego watering new plants?

Sure can’t. Rainfall is not cumulative. Do regular checks of newly installed trees and shrubs even after measurable rainfall. Water appropriately. Don't forget to overrride your irrigation system on days it's raining heavily and for a few days after substantial rainfall. Your plants will thank you!!!