Showing posts with label soil preparation. Show all posts
Showing posts with label soil preparation. Show all posts

Monday, January 18, 2016

The Nitty Gritty on the Down and Dirty

By Vanessa Spady


When it comes to growing iris, soil conditions will often dictate the quality and quantity of your rhizomes and blooms. Sure, other things make a difference as well—I for one think that a zesty combination of spoiling and neglect make for happy plants, but that’s for another post. About the soil...

Our little Comedy of Iris garden is located in central California, in a primarily agricultural area, which means we have a nice amount of space to start with (about an acre of open, slightly sloped land), but also some significant challenges when it comes to the dreadful native soil. As I mentioned previously, our soil has two basic textures—pudding when it rains, and concrete the rest of the time.

Luckily, the nutrient level is very low! (Hooray?) So trucking in good soil and amendments was a necessity. I had six yards of a really lovely loam delivered, and much to my astonishment, I have used it all. But, only the best for my newly purchased rhizomes, because, let’s face it, I want to see massive glorious blooms in the Spring!


Additionally, our hard ground is home to several kinds of critters that love it when we water—it makes the soil soft for them to dig through, and gives them something tasty and nutritious to eat. I, personally, do not like killing critters when they are in their territory, but no amount of reasonable conversation makes ground squirrels understand that they should go around the foundations of your barn when tunneling across your property. And gophers don’t care that the plant they just destroyed was a gift from your recently deceased mother... it was moist and tasty! Basically, any time you add water to our land, you attract the very vermin you want nowhere near your precious plants. Ugh.


Furthermore, it gets very hot here, and it’s quite dry. Because this is basically an irrigated desert, it’s over 100 degrees for weeks at time—so, really hot. And managing the watering (which requires more care during a drought) is also critical. Iris don’t like to be too wet (or they rot), and managing their moisture and nutrients is crucial for them to propagate and increase. But creating moisture means attracting critters that will eat their roots, if not the entire rhizome... wheeee?


So, even after we had good soil brought in, we faced challenges in keeping critters out of the beds, and not losing our stock to heat or rot. Time for some creative solutions.


When I was gardening back in my suburban setting, the soil was decent, critters were few, and the water was a spigot away... it was easy. All I had to do was not over-water, and feed once or twice a year, and I had gorgeous, happy iris all the time. After moving here, with the more challenging conditions, I have tried a variety of solutions, after losing most of a bed of named iris to a ground squirrel.


When I first planted iris in our country soil, they did so-so. I didn’t initially know how to manage the soil moisture and feeding was completely different here. But once I got it figured out, I saw lots of green growth, and happily awaited my first blooms. But they never came, and the number of rhizomes seemed to dwindle. Finally, a bit of loose soil at the back of the bed exposed the dirty truth: a ground squirrel had tunneled into the bed, from under my barn. He had been snacking on my lovely iris from beneath, and I hadn’t noticed him for weeks. This is when it started to get a little Caddy Shack...


I took up the few remaining iris, and dug out the entire bed to a depth of about one foot. I molded tight-weave chicken wire into an open-shoe box shape, and laid it into the hole where the bed had been. I then re-filled the bed, and planted a new batch of rhizomes, confident I had outsmarted the little blighter. Joke was on me, though. Several weeks later, as I was watering, I noticed a bump of loose dirt near the outside edge of the bed, and that dirt was moving.


“Ha!” I thought triumphantly to myself. “He’s just run into my chicken wire basket, and can’t tunnel his way through it!” I quietly laid down the hose, and watched to see what would happen. The little guy pushed the dirt out of the tunnel and popped his head above ground. I could see him looking around, so I held perfectly still. He ducked in again for a moment, then came up again, and to my outrage and astonishment, he got out of his tunnel, walked over the lip of the chicken wire barrier, and began to tunnel down into the bed, right in front of me!


The hours spent digging out the bed, making the chicken wire barrier, placing it in so carefully, and replanting the whole bed was undone in one moment. I had been played by a ground squirrel!


All bets were off after that. I dug up the remaining rhizomes from that bed and moved them into pots, but I never liked that solution, nor did my plants. Then I struck on using pallets as beds, which did a good job once I got the soil combination right. I placed the pallets on rocky ground, where the squirrels don’t really dig, and then filled all the slats with a combination of native soil, amendments, and planting mix. This
 had the added advantage of making it simple to keep iris from one bed or section from creeping into another section. I kept only one kind of iris in each pallet, and there was never any confusion. If we ever have an emergency, I can pick up the entire pallet and move it, bed and all. 


We knew from the beginning of this project that just digging up a little bed in the ground and plunking down the rhizomes was not going to be the method for success. For this initial growing year, we are trying a combination of kiddie pools mounted to pallets, raised beds (with a base of weed blocking cloth and wire mesh), and tires (with the same wire and cloth base). We cleared the surface of the soil of the dried and dead native growth (code for “weeds”), and began to layout the different kinds of beds we had to see how they might best work with the kinds of iris we ordered.


This was our preliminary layout, after we cleared the weeds, but before we put down the weed blocking cloth and wire. Ok, and before we painted the tires.


We opted to use only one level of these raised beds for this first year to see how they would do.

To give the iris the best chances for success, separating them from the ground was the smart move.  Besides, I don’t want to encourage any further comparisons between myself and Carl from Caddy Shack. 

The project has expanded considerably since this first phase, so you’ll have to keep your eyes peeled for updates and new photos. And you can bet there will be another load of the gorgeous loam heading our way sometime in the near future. Please, just don’t tell the gophers or ground squirrels.

And because I promised I would, here is a wonderful iris from Chris’ garden:


'Leave The Light On' Riley Probst, R. 2013) Seedling #U4WHXHM. IB, 22 (56 cm), Early, midseason and late bloom. Standards blue-purple with 1/16th gold edge; style arms bright yellow, vertical purple veining on style crests; falls blue-purple luminata pattern, bright yellow area with 1/4" white spear extending downward from beard; beards orange; pronounced sweet fragrance. 'Wild Hair' X 'High Master'. Fleur de Lis Garden 2013. Honorable Mention 2015.

Monday, July 8, 2013

Horticultural Vermiculite: For iris gardens from clay to sandy soil


It's almost time to dig and divide your irises... so now is the perfect time to take a look at soil amendments for better plant health. One of my favorite amendments is horticultural vermiculite. My southern bearded iris garden would not be possible without it, but even my moisture-loving Louisiana irises are happiest when this beneficial amendment is included in the soil blend. No matter what your climate or soil type, the addition of horticultural vermiculite can have a positive effect in your garden. 


'Flying Down to Rio' (Moores 2005) planted in vermiculite-amended soil

Vermiculite is a naturally-occurring geological material, more specifically a group of aluminum-iron magnesium silicates that closely resemble mica. When processed for horticultural use, vermiculite is introduced to intense heat, causing it to expand into multiple layers of very thin plates. The end result is accordion-shaped granules of sterile, disease-free planting medium. Vermiculite has been used by nurserymen and gardeners for decades, in potting soils and outdoor mixes, in turfgrass and outdoor plantings, for 100% vermiculite growing applications, and for hydroponic growing. Horticultural vermiculite improves soil aeration, assists in temperature regulation, and retains moisture and nutrients necessary to feed rhizome roots for superior growth.


Close view of coarse-grade horticultural vermiculite

Consider the following reasons for using horticultural vermiculite in your iris garden:
  • Soils amended with horticultural vermiculite are better able to retain air, nutrients, and moisture, and release them to the plant as needed. Therefore, a planting medium mixed with vermiculite promotes faster root growth for quick anchorage of newly planted rhizomes.
  • Because vermiculite has cation exchange properties, it holds ammonium, potassium, calcium and magnesium and makes these trace minerals available to the roots as needed.
  • Horticultural vermiculite is a perfect growing culture for irises. The pH of vermiculite is neutral to slightly alkaline (7.0-8.0). It will not deteriorate quickly like most planting materials, and it will not turn moldy or promote rot.

SOIL AMENDING OR CONDITIONING
Coarse grade vermiculite is preferred for outdoor horticultural uses, though medium grade may also be used. With heavy soil, the addition of vermiculite creates much-needed air channels to greatly improve soil aeration. When soil is sandy, the addition of vermiculite helps the soil retain much-needed moisture. Soils may be amended up to a rate of two parts soil to one part vermiculite.

With a large garden area, you may choose to condition only the planting rows. If this procedure is continued for three to four digging cycles, the entire garden area will eventually be conditioned. Because horticultural vermiculite is inorganic, it will continue to function for many years.

Medium grade vermiculite is preferred for potting applications. When used in potting new rhizomes, vermiculite improves soil aeration and diminishes the risk of tender roots breaking as the irises are transferred to the garden. If starting with commercial potting soil, check the label before adding vermiculite, as it may already be present. If making your own potting mix, vermiculite may be added up to a ratio of one part compost material or soil to one part vermiculite.


Planting mix of two parts soil and one part horticultural vermiculite

SUMMER MULCH
If you live in an area that has little to no summer wind, you can use vermiculite to mulch around the rhizomes in the hottest summer months. Vermiculite acts as a constant reservoir of moisture without promoting rhizome rot, protecting your irises from dehydration and scorching during dry spells. This can be especially helpful immediately after digging time, when replanted rhizomes are settling in. After the intense heat passes and winds return, you can remove the vermiculite mulch and save it for use in potting or amending the following year. Or, you can mix it into the soil in other areas of your garden. Used as a mulch, vermiculite may be applied up to 3 inches thick.

FLORAL ARRANGEMENTS
After your irises begin blooming, you will want to bring some of those lovely blooms inside to enjoy. Fill a vase with vermiculite, saturate with tap water, and allow the vase to sit for a few minutes. Repeat this process until the vermiculite is no longer absorbing and water is visible on top. Then, pour off the excess water. Arrange your flowers as you would normally. Your flowers will remain fresh for many days without refilling, and the stems won't develop that unattractive slime that normally occurs when a stem sits in water. When placing flowers in vermiculite, be sure to cut the stems at a slight angle to facilitate wicking.


Flowers being arranged in a vase filled with water-saturated horticultural vermiculite

HOLDING OR SHIPPING RHIZOMES
Vermiculite can also be used at digging time. After you have provided a bleach bath for your newly dug rhizomes, allow them to air dry in the sun. Be careful not to let them bake; the idea is to let the exterior dry without dehydrating the interior. After the rhizomes are fully dry, place them in a storage container and pour vermiculite around them. The vermiculite will prevent moisture fluctuation during the storage period and will provide protection against temperature changes. Though iris rhizomes should never be stored long-term like a bulb, use of vermiculite allows your rhizomes to stay fresh many days longer before replanting. An exact length of time cannot be predicted here, as the timing is dependent on the hydration level of the rhizome (internally) prior to placement in the vermiculite. Vermiculite can also be used when shipping rhizomes to friends.


Rhizomes being placed into a shipping box filled with horticultural vermiculite

A FEW WORDS ABOUT SAFETY
In the past, you may have heard about a link between vermiculite and trace amounts of asbestos. For almost seventy years, vermiculite was used safely and effectively for many purposes, including construction and industrial applications. Then, in 1990, asbestos particles were discovered in vermiculite originating from a mine in Libby, Montana. This mine was primarily used to produce vermiculite for industrial, not horticultural, applications, under the tradename Zonolite. The discovery brought worldwide production of vermiculite to a screeching halt as scientists and regulators worked to determine if any other mines were contaminated. Since that time, strict inspection and safety procedures have been put in place. Though a warning label may still appear on the bag due to past Libby-related incidents, vermiculite is not listed on the OSHA List of Hazardous and Toxic Substances. Gardeners can feel confident that the horticultural vermiculite found in stores today is non-toxic and safe for use in their garden. Just remember, it is wise to use caution when working with dusty garden amendments of any type, including use of a dust mask and watering the garden area prior to application. 

What amendments have been useful in your garden? Post your comments below!

Learn more about horticultural vermiculite with these resources:
Material Safety Data Sheet for Vermiculite, SunGro Horticulture, issued March 1, 2008. This publication details the chemical and physical properties of vermiculite, verifies that vermiculite is not considered a hazardous or  toxic substance by OSHA, and provides useful supplemental information.
EPA Sampling and Analysis of Consumer Garden Products That Contain Vermiculite, August 2000. This report details the results of the first large-scale study of consumer garden products that contained vermiculite. Since the publication of this report, significant advances have been made in the processing and inspection of horticultural vermiculite sold to consumers.