Thursday, March 19, 2009

Amazing Ivy by Gardener Dave

Boston Ivy

Are you an “Ivy Fan”? I am – up to a point. I use English Ivy (Hedera helix) as a groundcover for shade and semi-shade, and Boston Ivy (Parthenocissus tricuspidata) as a wall climber/cover in sunnier areas. Ivies can be used to “soften” a bare wall behind other plantings and provide added cooling and humidity in our dry climate. They can help to alleviate scorching and discourage spider mite infestations in sunny walled areas.

Part of my fascination with ivy is its ability to cover large expanses of ground, walls or fences quite quickly. I also like the evergreen (depending on our winter) qualities of English Ivy, and I like the fall reddening of Boston Ivy. I am also fascinated with the clever means by which these ivies climb walls and other vertical surfaces.

There are many other “ivies” and climbing plants that use different means of attachment, such as tendrils which wind around any supporting structure (and itself) in order to reach and grow upwards. I am only detailing here the ivies with which I have had personal experience. I also have some Virginia Creeper (Parthenocissus quinquefolia) – also sold as Engleman’s Ivy – coming into my yard from a neighbor’s. It does turn red in the fall, and it is very hardy, but it can be extremely invasive, and it is susceptible to powdery mildew which can spoil the fall color. Of the three types, English Ivy is the only one that is “evergreen” here (* See “Cautions” below).

In 1865, Darwin wrote about ivy at length in his book The Movements and Habits of Climbing Plants. The following are some of my own observations: My English Ivy has little “rootlets” that grow sideways from the main stems and take advantage of any little spaces on brick or stone walls, fence slats (or almost anything) to wedge itself in. The “rootlets” also adhere to surfaces very tenaciously. My Boston Ivy has little “feet” or “hands” growing from the main stems (please excuse my not using botanic terms for these appendages). Each “foot” has several little separate sticky pads that can seemingly attach to ANY surface with an extremely strong glue-like bond. They even attach to undersurfaces such as eaves and patio ceilings!

English Ivy

Geckos are famed for their ability to walk on walls, thanks to nanoscopic hairs on their feet called “setae”. http// Ivy uses another nano-scale trick to defy gravity. Several articles I have read lately describe an exuded form of “nano-sized [cementing] globules” that allow ivy to cling tightly to surfaces. Researchers at the University of Tennessee in Knoxville have studied the process in depth, and say their tests reveal something like 19 different primary compounds in the ivy bonding process. I promise I won’t go into the chemical analysis of their research, but they report that millions or even billions of weak adhesion or hydrogen bonds (not bombs!) that the ivies produce, add up to make a very strong adhesion to climbing surfaces.

Researchers are also working on ways to counteract these forces with the goal of making paints that can protect surfaces from ivy damage. Also, researchers at University College Dublin in Ireland think that “…studying plants like ivy could uncover entirely novel nano-materials.” Perhaps new “miracle” adhesives?

Cautions: My ivies are not parasitic; they do not obtain nourishment from the trees, etc. that they climb on. But they will take advantage of any surface they can get their little “rootlets” into, “sticky pads” onto, or “tendrils” around. My ivies climb my brick house walls and fences and trees in my yard. They can also creep into windows and between (fairly tight) window panes. It looks “quaint” on a house wall and adds green interest to the overall landscape, but if you want to remove it, it can pose some problems. In our dry climate, the problem takes the form of leftover adhesions when you pull it off. A paint scraper or similar tool can help remove them, but they will never come off 100% unless the surface is vigorously sanded. Also, (*) English Ivy may winterburn in more-exposed areas, losing attractiveness and requiring some trimming back in Spring.

By way of interest – in moist climates, large overgrowths of ivy can bring down weakened tree branches, and its long-term decay against brick or stone walls can form humic acid which is capable of dissolving carbonate stone and some mortars. I seem to remember reading where some ivies are considered noxious weeds in moist climates, but in our area this should not be a problem with the three types I have mentioned.

Virginia Creeper

So – as I said earlier – I am an “Ivy Fan” up to a point. If you are willing to cut them back when you need to, they can be a nice green addition to your landscape. Don’t let them become too invasive, especially the Virginia Creeper or Engleman’s varieties. I have learned my lesson. Use them with this in mind and you will be happy with them. They are interesting, useful and decorative plants.

Gardener Dave

Saturday, March 7, 2009

Sneaky Water Bandits or “The Great Rain Robbery” by Gardener Dave

How Much of This Will Get To Your Roots?

There are some subtle, perhaps even “insidious” natural forces at work “stealing” our water. When we hear reports of several inches or even feet of snow in our watershed areas, in the foothills, or (rarely) even on the plains near Denver, we really can’t assume that is the amount that will finally be available to us. Let’s look at these natural forces, and let’s ignore the water absorbed as it moves downslope to reservoirs. That part is very beneficial to trees, shrubs and other vegetation – I don’t consider that to be “stolen”. But, as an old English proverb says: “There’s many a slip ‘twixt the cup and the lip”.

1) Sublimation – This process turns snow directly into a gaseous state, bypassing the beneficial liquid water state entirely. I have no actual estimate of how much of our snow moisture is lost by this process, but it can be significant, and we certainly need all the moisture we can get. Have you ever noticed that sometimes snow can shrink a lot even before we get the warm Chinooks and sunshine? Some shrinking is from compaction, and some is because of sublimation.

Sublimation occurs at below-freezing temperatures. It is the same phenomenon used in the commercial freeze-drying process. It also explains why Grandma could hang her clothes out on the line in below-freezing temperatures and later retrieve them all nice and dry. Our very dry and many times fast-moving winter air also accelerates the sublimation process. In case you’re interested, this is also how “frost-free” freezers keep their walls and shelves free of frost and ice, by using a fan within the freezer compartment to circulate dry, cold air. Even ice cubes in open trays will sublime and get smaller if left unused for a long time.

To further illustrate the sublimation process by way of something that we may be more familiar with, frozen carbon dioxide (dry ice) sublimes at atmospheric pressure and room temperature. That’s how our stage acts, plays and movies create all that spooky “fog”. The opposite of sublimation is “deposition”. Frost is an example of this. In frost deposition, water goes from a gaseous vapor directly to solid ice crystals.

2) Evaporation – We lose a lot of water by evaporation, especially from the surfaces of reservoirs, lakes and even streams. Again, our dry air and winds speed up this process. We are all familiar with this process, so I won’t belabor it here, except to give you an estimate of how much water can be lost. For arid regions, I have seen estimates of over 25% of the water, stored to be used for human purposes, can be lost to evaporation.

3) Virga – You may have said “Gee, look – it’s really raining heavily from that cloud”, only to find out that it never actually reaches the ground at all. And – you guessed it – our dry air also contributes to this effect.
Now, in my mind, virga qualifies as one of our Sneaky Water Bandits because if we see rain falling from the sky – it sure would be nice if it reached the ground and soaked into our lawn and gardens… oh well, maybe some other time!

The word virga is derived from Latin, meaning twig or branch (go figure that out), and a popular “backronym” (ever hear that word?) in meteorology is "Variable Intensity Rain Gradient Aloft”. (See, we learn something every day if we pay attention). Interestingly – one effect of virga can be pockets of cold air that descend rapidly, creating dry air called microbursts which can be extremely hazardous to aviation.
4) Run-off – When we see water running downhill we can all spot this one, right? But perhaps less-known is the fact that all the water that falls on our property doesn’t actually belong to us. According to Colorado Water Law, we can’t just use rain-barrels on our downspouts or a big catch basin to retain every possible drop. I may be selfish if I consider this run-off water “stolen” (from me), but if rain falls on my property – I’d like to keep it!

However – Colorado Water Law requires that precipitation fall to the ground, run off and into the river of the watershed where it fell. An individual may not capture and use water to which he/she does not have a right. Also… the reuse of household water (gray water) is regulated by Colorado State Board of Health Guidelines. Colorado Water Law allows each customer just one use of the water before it goes down the drain, through a wastewater treatment plant and back into the river for others to use. By law, Denver Water customers are not permitted to take their bath or laundry water (“gray water”) and dump it on their outdoor plants or garden. After this water is used once by Denver Water customers, it must return to the South Platte River where it will be used seven or eight more times before it gets to the state line (Nebraska).

Gardener Dave