Monday, December 10, 2012

Season's Greetings!

Welcome back to the first of the holiday episodes of Lost In The Farmer’s Market where we examine the horticultural trends as though we were a horticultural Myth Busters on steroids! Today we have the promised continuation of the house plants-oriented discussion but also a special additional discussion regarding a common but often misunderstood occurrence in most gardens on the east coast of the United States.  Since we are in the early days of the winter give or take the occurrence that has been included in today’s discussion is frost.

This Lemon Drop Pepper plant is showing the immediate after-effects of frost exposure, it is still green but all soft tissues have collapsed making the plant look wilted.

Commonly frost is thought of as what happens when a plant freezes and typically dies afterward. This assertion is partially true; yes frost does its damage through freezing of a plant’s soft tissues. There is no doubt that for the gardeners in the north east the dead annual plants have stacked up already. In the southeast particularly Fayetteville we have had several incomplete frosts starting around the second week of November.

In this case a much more hardy Lemon Verbena shows the typical scorching of leaf tips inward. Note that frost damage missed the actual growing tips of this herb entirely yet the peppers in the earlier picture, which were much taller were wiped out. The two plants were inches away from each other in the same garden bed.

For clarity, frost is what occurs when the ambient air temperature is 32 degrees or less and an exposed plant suffers severe cellular damage. Typically the cold itself causes cells in leaves and stems to freeze causing the cell walls to burst as the water contained within expands. This effect is devastating to the plant and should it survive it is often stunted and mangled never quite being able to return to its former stature in most cases. The effect is similar to frostbite for a human being, as the damaged areas are effectively dead and begin to go necrotic as other decomposing organisms often move in. The amount of humidity in the air can effect which type of frost is visible in an given area, typically either frost or hoar frost.

This sweet basil was utterly destroyed. Apparently having frozen and thawed more then once overnight you can see where the early stages of necrosis are occurring in the brown portions of the leaf tips. Annuals such as basil are very dramatic in displaying the effects of frost injury.

Normal frost manifests itself as clear ice crystals on surfaces; typically it’s the glittering stuff you see in the lawn as you walk across it in the morning on a cold day. In that case specifically the frost is formed from morning dew that has frozen in the leaf blades of the grass. More often then not you will not see this frost but you will see its damage the next day. In exceptionally long periods of cold this sort of frost

Hoar Frost which mind you is so much fun to say is the sort of frost that results when there is higher ambient humidity in the air. Hoar frost manifests itself as white or gray ice crystals on surfaces that often take on very unique patterns. On plants Hoar frost will show it’s damage like traditional frost however, some times across leaf surfaces it will miss an area or leave entire leaves alone. The name Hoar while fun to say does not mean the same thing as Whore in fact something described as ‘Hoary’ has a white or grey fuzz or light hair of the same color.

This rose scented geranium persists despite exposure, it's fuzzy leaves no doubt negated some or most of the killing frost's effects.

In this image you can see the areas of damage as the tan colored dead areas at the leaf tips. Frost damages by dessication as much as it does by cold thus it makes sense the leaf tips are what get damaged the most. In the case of the basil above since the leaf margins die first it makes sense that necrosis occurs there first and decomposing organisms such as mold and bacteria appear there first.

I admit the frost situation sounds bleak, but there are a few things you can do to save your prized tender perennials and or annuals from the ravages of frost. If the plant in question is a perennial that has been planted recently or still is in a pot make sure to water it but do not get the foliage wet if possible.  Tender perennials under the same circumstances will require watering and protection perhaps by temporarily burying them in leaves, wrapping them in burlap or fabric or if posted being moved to a more protected location. Annuals present a tougher alternative, it is easiest to move them indoors or take cuttings but alternately if this is not heavy protection may be the only way to protect such plants. Moving onwardto something cheerier today's plant selections involve two succulents from the Heurnia family.

The lifesaver cactus is named for the red ring on the flower as seen above which resembles a cherry life saver candy.

You can identify a lifesaver cactus by the fact it has four rows of fleshy spines, but the stems contain no glochids, thorns or other prickly bits.

Dragon Cactus seems to get it's name from the impossibly red sparkling flowers. In the right light the flowers sparkle as if their petals are composed of the scales of some lizard. They are a bit on the small side but appear in numbers from September through January.

Unlike the life saver cactus the Dragon Cactus has six points on the stem. It also lacks any thorns or glochids on the stems making it equally easy to handle.

Heurnia’s not to be confused with Hernias are commonly confused with the Stapellia family of succulents and both are often commonly called starfish cactus. The two are somewhat related however the most obvious difference is the fact that Heurnia lack a well known trait of the stapellia group. Stapellia are commonly also known as carrion flower for the coloration of their flowers which resembles bloody meat and the scent resembles road kill. The heurnia typically have similar flowers but without the smell and as you can see in the pictures included today, great variability in shape. The first plant is commonly called Lifesaver Plant, as you can see in the photo this is because it has a unique red ring in the flower which is quite unique. The second plant is called Dragon Cactus for its fiery red flowers which when combined with the pointy foliage resembles a fire breathing dragon perhaps.

For note the Heurnias are members of the Apocynaceae family which also includes Plumeria, Vinca, Oleander (Nerium) and Madagascar Periwinkle (Catharanthus). For the succulent enthusiasts out there this group also includes Pachypodium, Ceropegia (String of Hearts) and, Adenium (Desert Rose) all three of which can be found in the trade readily.

In terms of care, the one thing to remember is that Heurnias do not like to have wet foliage or constantly wet soil. If kept we you can be sure to see how devastating root rot can be to a succulent. The good news is that if you do mess up and root rot sets in you can take a 2-5” long cutting allow the end to dry out and try to start a entirely new plant. Occasionally a heurnia will drop stem segments of its own volition and these ‘natural cuttings’ can be potted up as new plants without delay.   

While photographing these plants as if on cue the Dragon cactus shed three stems. Occasionally these plants will shed even while not under stress of any sort.
The soil you use is not important as long as it is not heavy in clay, any normal potting mix or cactus mix will do as long as you adjust your frequency of watering to compensate for the moisture retention of the soil. It is important to remember that hernias can tolerate nearly year-round exposure but must be protected from freezing. Hernias will also do well in full sun in the north east but down south may need some protection in the south to avoid scorching.

This concludes this week’s episode of lost in the farmer’s market, I hope you enjoyed these plant ideas and found the information about frost useful. In the next post I will be discussing another interesting set of plants and a garden oriented topic, thank you for reading and remember folks Keep ‘em Growing.


  1. I just recently purchased a Heurnia that is of the monstrosus type. I seperated one long growth with the intent to replant in another pot. I am waiting now for the wound to heal. The grower advised me that he has never seen this plant bloom. I plan on taking some photos today.

  2. Interesting; I'm curious though, do you mean Monstrose (ie deformed) or monstrous as in Larger? The stapellias and Heurnias are within the same family and generally the former is bigger then the latter. For note, stapellias are called carrion flowers because the blooms smell like road kill.