Cold Hardy Evergreen Oaks

Southern Live Oak
Southern Live Oak

There are a number of Cold Hardy Evergreen Oaks species that can grow in USDA Climate Zone 7 and even Zone 6. Quercus virginiana is commonly called Live Oak. This tree has a natural range from the southeastern part of Virginia through Southwestern Oklahoma through Texas into Northeastern Mexico.These are very distinctive trees. They are the iconic tree of the Deep South. They have a unique shape that is hard to miss. They can be wider than they are tall. They can reach from 40 to over 60 feet in height and from 50 to 100 feet in width. These heights and spreads are for trees in good conditions in their natural range. Trees grown in colder climates will not usually be as massive. The crown provides a dense shade and the individual leaves are shiny dark green with a length of up to 6 inches and a width of less than half an inch to 2 inches.

Live Oaks retain their leaves almost year round but are not true evergreens. They drop their old leaves in spring immediately before new leaves emerge. On Occasion this tree can be more like a semi-evergreen when grown in colder climates. The leaves will stay green until the the temperature get close to 0 Fahrenheit. The temperature can vary slightly based on tree health, moisture etc. The bark is thick and dark and can be deeply furrowed. These trees prefer sandy soil or sandy loam but they will grow in clay. They prefer a decent amount of water but once well established generally don’t need supplemental water. These are deep rooted trees which helps with the hurricanes they deal with in the coastal plain in their native range. These trees are able to deal with salt spray near the coast as well as dealing with some soil salinity. These are very long lived trees. There are trees that were planted in the 1700’s that are alive and well today.There is such a thing as cold hardy southern live oaks. This is a solid zone 7 plant.There are people who are growing these trees in USDA Zone 6 and even Zone 5.

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There are some related varieties of Live Oak that also should get mentioned. Quercus fusiformis also commonly called Texas live oak it differs from the common Southern Live Oak in that the acorns are bigger and the tree itself is smaller.It can reach from 25 to 40 feet in height. This tree can take dryer conditions and also may be slightly hardier than Southern Live Oaks.

Quercus geminata is commonly called Sand Live Oak. It is native from Southern Virginia through Southern Florida and along the Gulf Coast. It grows in sand dunes and forms scrubby forests. It is a smaller tree than the Southern Live Oak. In most cases it grows to around 50 feet tall but in exceptional cases can grow over 90 feet tall. It has thick bark and shiny leathery leaves that are around 2 inches long. So far I have not been able to find cold hardiness information for this tree but I suspect it is similar to the Southern Live Oak. Due to its nature of growing in sandy dry places it may have some greater cold tolerance as sandy barrens can get much colder than surrounding areas in winter due to radiational cooling.

Quercus minima is commonly called the Dwarf Live Oak or Minimal Oak. It is found in the Southeastern United States. It is a small tree growing no larger than 7 feet tall. It may have some potential for cold hardiness especially being a smaller plant but I have yet to find information regarding that.

Quercus turbinella is commonly called Sonoran Scrub Oak and Grey Oak it is native to the Southwest United States and Baja California. It’s range is as far north as Utah and Colorado. It has spiky leaves and usually stays a shrub under 20 feet though it can sometimes grow larger. Due to its more northern and mountainous range this species may have considerable potential as one of the most Cold Hardy Evergreen Oaks

Quercus chrysolepis this is commonly called the Canyon Live Oak. It is native to the West Coast of the United States from South Central Oregon all down the Pacific Coast of California. There are also populations of the tree in Nevada, Arizona and New Mexico. It also grows in northern Mexico. The leaves are glossy and they can reach from 1- 3 inches in size. It can be a shrub under 20 feet in size to a tree of over 100 feet in some cases making it one of the larger Cold Hardy Evergreen Oaks. This tree is quite hardy and can withstand below zero Fahrenheit temperatures.

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Quercus vacciniifolia this is commonly called the Huckleberry Oak. It is a very small shrub usually under 5 feet in height. The leaves are small and leathery. This tree is native to the mountains of Southern Oregon,California, Nevada and into Northern Mexico.I have not been able to find cold hardiness information yet on this plant but I would guess it may be fairly cold hardy due to it being native to higher elevations.

Quercus hemisphaerica is commonly called Sand Laurel Oak or Laurel Oak is a evergreen to semi-evergreen tree. It can grow fairly large over 100 feet although it is usually smaller around 60 feet or so. This is one of those plants that the colder the conditions the less evergreen it will be. The leaves are around 1 inch to almost five inches in length. It prefers sandy soil. The tree is native to the coastal plain from Delaware to Eastern Texas.

Quercus myrtifolia is commonly called Myrtle Oak is a shrub to small tree that can reach up to 40 feet in height on occasion. it is native from Coastal South Carolina to Florida and along the Gulf Coast to Mississippi. I have not been able to find hardiness information yet regarding this plant.

Quercus myrsinifolia is commonly called Bamboo Leaf or Chinese Evergreen Oak. It is native to South Korea, Japan, China, Laos, Thailand and Vietnam. It can grow up to around 70 feet in height. I have not been able to find cold hardiness information yet for this plant but seeing that it is native to South Korea makes a good case that it may be fairly cold hardy.

Quercus stenophylla is native to South Korea, Japan and Taiwan. I have not been able to find cold hardiness information yet for this plant but seeing that it is native to South Korea makes a good case that it may be fairly cold hardy.

Quercus semiserrata is native northeastern India, Bangladesh, Myanmar, Thailand, small parts of China and Tibet. This is a small tree to usually is under 30 feet tall. I have not been able to find cold hardiness information yet for this plant but it is native to higher elevations and it may be fairly cold hardy.

Quercus oxyodon is native to Tibet, Bhutan, Myanmar and Northern India and Southern China. This tree can grow to around 60 feet in height. I have not been able to find cold hardiness information yet for this plant but it is native to higher elevations and it may be fairly cold hardy.

Quercus glauca is commonly called Ring-Cupped Oak or Japanese blue oak it is native to South Korea, Southern Japan, China,Nepal, Bhutan, Northern India, Afghanistan, Myanmar and Vietnam. This tree can grow to around 60 feet in height.I have not been able to find cold hardiness information yet for this plant but it is native to higher elevations and it may be fairly cold hardy.

Quercus acuta is commonly called the Japanese Evergreen Oak. it is native to South Korea, Japan, Taiwan and China. I have not been able to find cold hardiness information yet for this plant but seeing that it is native to South Korea and Japan makes a good case that it may be fairly cold hardy.

I will keep researching this topic and I hope to get more information about Cold Hardy Evergreen Oaks. Many of the Asian species have promise I believe and I will update the post when I get more information.

Cold Hardy Southern Magnolias

 

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Cold Hardy Southern Magnolia in Philadelphia PA.

There are a number growing number of gardeners who are successfully growing Southern Magnolias outside the southern United States. Their natural range is the deep south of the United States. The states in the natural range of this tree include North Carolina, South Carolina, Georgia, Alabama, Mississippi, Louisiana and Texas. In their native habitat they can become very large trees over time. There are some older trees that are over 120 feet tall. They can grow from 1-2 feet a year in good conditions which is considered a slow growing tree. Their natural shape is somewhat like a pyramid with older trees sometimes growing quite wide. This is a broadleaf evergreen tree with large shiny dark green leaves that can be 5-8 inches long and 2.5 to 5 inches broad. The flowers are very showy and large. They are white and up to 12 inches across and have a very sweet fragrance. Southern Magnolia like a well watered but not boggy location and rich soil on the more acidic side. Partial shade to full sun is ideal.

In my personal travels I have seen Cold Hardy Southern Magnolias in Columbus 6A and Lancaster 6A Ohio as well as several specimens in the Toledo Ohio 6A, 6B area. I have also seen them in Philadelphia 7B and Washington D.C. 7A Some of the specimens in Washington D.C. are very old and massive. From my research trees in the wild or trees grown from seed collected from wild trees appears to be hardy to Zone 7A.

Southern Magnolia leaves and flowers
Southern Magnolia leaves and flowers

There are several cultivars that appear more cold hardy than the wild variety. There are two cultivars I am going to mention. The first Cold Hardy Southern Magnolias cultivar is Brackens Brown Beauty. This tree develops a dense canopy with smaller leaves than the wild variety. This is the variety that I have seen planted in Ohio and is possibly cold hardy to Zone 5B. The other cultivar that I have seen tried in the north is Edith Bogue. This is a vigorous tree with a pyramidal shape. Both of these cultivars are worth trying in colder climates than wild grown trees could tolerate. These can grow to decent size trees over time but don’t expect them to get as large as they would in the deep south.

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Cold Hardy Palms 101

The ultimate symbol of tropical or subtropical climates is the palm tree. That is why I wrote a post on Cold Hardy Palms 101. Many of us go on vacation to Florida or other warm climates and see the beautiful palm trees. While it is true that palm trees generally are native to warmer tropical or subtropical regions there are some species that are native to warm temperate areas and some that will grow in parts of the northern United States and Canada. The term cold hardy palm trees is a relative term. It all depends on what people mean by cold hardy. Is being able to withstand 10F cold hardy or what about 0F and for how long? Also some trees can stand colder temperatures in dry sandy soil or if they are in a location that is out of the wind.

There are two main kinds of palm trees. There are Fan palms and feather palms. Feather Palms have the type of leaves that a Coconut Palm has. Fan Palms have the type of leaves that Palmettos have. These are the familiar palm trees from Myrtle Beach. Generally speaking fan palms are hardier than feather palms.

In this article I am going to focus on palms that have a shot in climates that are Zone 7B and colder. The average minimum winter temperature in Zone 7B is 5-10F. The USDA has climate zones for the entire United States. These climate zones are separated in 10 degree F increments with half zones in between. Some cities in Zone 7B include NYC, Philadelphia, and Atlantic City etc.

In this article I am going to focus on palms that have a shot in climates that are Zone 7B and colder. Specifically gardeners in zones 5A to 7B. There are people that grow palms outdoors in climates colder than 5A but the winter protection involved can get pretty elaborate. For zones warmer than 7B you start to see a number of palm varieties out in the open with no winter protection. In future blog posts I will go into ideas for winter protection and report on other varieties of cold hardy palm trees when I find out about them.

The 2012 USDA Plant Hardiness Zone Map is the most commonly used climate zone map in the United States. This map was updated since the last edition came out in 1990 and the end result was that many locations moved a half zone or even a full zone warmer.

2012 USDA Plant Hardiness Zone Map
2012 USDA Plant Hardiness Zone Map

2012 USDA Plant Hardiness Zone Map
2012 USDA Plant Hardiness Zone Map
Zone 5B Major Cities

Lansing MI, Colorado Springs CO, Chicago IL, Denver CO, Des Moines IO, Omaha NE, Albany NY, Portland ME,

Zone 5A Major Cities Casper WY, Rapid City SD, Madison WI, Burlington VT, Bangor ME,

Zone 6 A Major Cities Durango CO, Topeka KS, Fort Wayne IN, Ann Arbor MI, Columbus OH, Buffalo NY, Springfield MA,

Zone 6B Major Cities Santa Fe NM, Wichita KS, Kansas City MO, Evansville In, Toledo, OH, Pittsburgh PA, Providence RI

Zone 7A Major Cities Boise ID, Grand Junction CO, Tulsa OK, Nashville TN, Richmond VA, Boston MA

Zone 7B Major Cities Albuquerque NM, Lubbock TX, Tupelo MS, Chattanooga TN, Charlotte NC, New York City, Parts of Cape Cod MA

 

 

Trachycarpus Fortunei Commonly Known as the Chinese Fan Palm
Trachycarpus Fortunei Commonly Known as the Chinese Fan Palm

Trachycarpus Fortunei

Commonly called the Chinese windmill palm this is most likely the coldest hardy trunked palm. There are various reports of the hardiness of this palm. In my research I have seen it listed as hardy from up to -10 F to 10 above F. My personal opinion is that it is hardy to somewhere between 10F and 0 F. I have grown small specimens using winter protection (Styrofoam Rose Cones) in Toledo Ohio Zone 6 B Climate. These plants are native to Mountainous regions of Central China, Southern Japan and Burma. They can grow up to 35-70 ft. tall in ideal conditions. They generally prefer cooler wet shady conditions except when planted in colder climates where they can take sunny conditions.

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Commonly called the Takil Palm
Commonly called the Takil Palm

Trachycarpus takil

Commonly called the Takil Palm this tree is native to areas of northern India and Nepal. It grows in higher altitudes in areas that can get snow in winter. This tree is native to areas of high humidity so regular watering is important. It can grow from 30-50 ft. in height. From my research it may be hardy from 5F to -5F. It is not common in cultivation yet. It is an attractive tree that looks similar to the Chinese windmill palm.

Nannorrhops ritchiana

Mazari Palm

This is a rare shrubby palm native to desert regions of Afghanistan, Pakistan and neighboring countries. It is reportedly very cold hardy with reports of it possibly being hardy down to -4 F. It is a picky plant and does not like damp conditions. This might be worth a try in warmer areas of New Mexico, Utah, Colorado and other areas with similar climates.

Sabal ‘Birmingham’

This plant appears to be a hybrid between Sabal Minor and Sabal Palmetto. The first time this plant was identified was in a garden in Birmingham Alabama. The plant was said to have survived may freezes over the years of 10F and at least one freeze of below zero. The original tree died sometime after it was transplanted but there are many descendants of the original tree that have been grown from its seed. Some of these trees have survived temperatures well below zero. It is a slower growing tree than Sabal Palmetto but it does grow a trunk and can reach a height of around 40 Ft. My guess would be with my research that this plant is hardy to somewhere between 10-0F with well sited healthy specimens with some winter protection hardy to -5F. This palm would most likely be pretty safe in a Zone7B area and in the right microclimate might make it in 7A or 6B.

 

Sabal minor Commonly called the Dwarf Palmetto
Sabal minor Commonly called the Dwarf Palmetto

Sabal Minor

Commonly called the Dwarf Palmetto this palm is usually trunkless and grows to around 3 ft. tall in most cases. In some cases after many years it can develop a small aboveground trunk and grow up to 9-10 ft. tall. This is one of the hardiest of the palms. These palms are native the southeastern US as far north as the southern tip of Virginia and southern Arkansas and Oklahoma. They also range into northern Mexico. The variety McCurtain from southeast Oklahoma is the hardiest known variety of sabal minor. It has been reported to survive -10-20 F without major damage.

 

Rhapidophyllum hystrix Commonly called the Needle Palm
Rhapidophyllum hystrix Commonly called the Needle Palm

Rhapidophyllum hystrix

Commonly called the Needle Palm this is probably the hardiest palm in the world. It is a trunkless palm in most cases but sometimes will have a short trunk. It can grow from 6- to 10’ ft. tall. It is native to Florida, Georgia, South Carolina, Alabama and Mississippi There are reports of the plant surviving -10-0 degrees. At 0 degrees or below expect some damage. Generally speaking this is a plant that likes hot summers. It is a good bet to try in parts of the eastern United States that are too cold for the larger trunked palms. There are needle palms along the Atlantic Coast including in New York City. This plant is known for having large needles or spines around the base. These needles can be from approx. 4”-10” long. They protect the plant from grazing animals in the plants native habitat.

 

Sabal palmetto Commonly called the Cabbage Palm
Sabal palmetto Commonly called the Cabbage Palm

Sabal Palmetto

Commonly called the Cabbage Palm this is a trunked fan palm that is common on beaches in the Southeastern US. These palms are very common in Myrtle Beach. They are native to the southeast US from coastal North Carolina to Florida and in the coastal plain of the states bordering the Gulf of Mexico. They commonly can reach from 40’-60 ft in height and in some exceptional cases up to around 90 ft. in height. I have seen reports that they are hardy down to 7-15 F. As with many palms it is the duration of the cold as well as how cold it is that is important. The coastal southeast gets periodic cold snaps but usually they are short lived.

 

Chamaerops humilis Commonly called the European fan palm
Chamaerops humilis Commonly called the European fan palm

Chamaerops

Commonly called the European fan palm this palm has the most northerly native range of any palm. It grows as far north as Latitude 43. This is the same latitude as Boise Idaho and Rochester New York. The difference being in Europe to the north and west is the Atlantic Ocean and not Arctic Canada. The natural range of the species is the Mediterranean basin and adjoining areas. This is a fan palm which usually grows in a shrubby manner with multiple trunks and growing from 4-20 ft. in most cases. It is hardy down to 12-8F for short periods. This plant does not like prolonged cold spells. It comes from places with a Mediterranean climate so for those experimental gardeners it may do best out west in lower humidity areas.

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Serenoa repens Commonly called the Saw Palmetto
Serenoa repens Commonly called the Saw Palmetto

Serenoa repens

Commonly called the Saw Palmetto This is a shrubby fan palm which usually does not develop a very tall trunk. It grows very slowly and can spread out over great distances. It can grow from 7-10 ft. tall after a long period of time. These palms are relatively common in Florida and adjoining areas of the southeast and grow in open pine forests and also along the coastline. This palm has spines along the stem and this is where it gets its common name Saw Palmetto. From my research it appears that the tree can survive from 5-0 F.

 

Butia capitata Commonly called the Jelly Palm
Butia capitata Commonly called the Jelly Palm

Butia Capitata

Commonly called the Jelly Palm this is a feather palm. This palm is native to Argentina, Paraguay, Brazil and Uruguay in South America. It can grow rather tall. It prefers full sun to partial shade. It can grow to around 20 ft. tall and in exceptional cases 30 ft. tall. In researching this plant I have seen it listed as hardy from 14 F to 5 F. This would place it in zones 7-8. This is a common plant in the coastal southeast. It is naturalized as far north as Virginia. It does not like extreme heat. There are specimens growing as far north as New York City on the East Coast and Coastal British Columbia on the West Coast. They have fruit which are used to make jelly and wine.

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Butia Eriospatha

Commonly called the Woolly Jelly Palm this is less common in the US than the Jelly Palm. It is a 15’ tall slow growing feather palm native to southern Brazil and northern Argentina. It prefers full sun to light shade. Is hardy without damage to around 15F and there are reports of it surviving below 10F.

 

Jubaea Chilensis Commonly called the Chilean wine palm
Jubaea Chilensis Commonly called the Chilean wine palm

Jubaea chilensis

Commonly called the Chilean wine palm this plant is native to central Chile. It can get up around 80ft in height and has a thick trunk that can grow over 4ft wide at the base. It is hardy down to 5F for short periods. It would not do well in an area with extreme cold all winter. These plants do best on the west coast from southern British Columbia to Southern California. There are also specimens in Arizona and New Mexico.

I hope this post was helpful for you. I will be updating it in the future.

Microclimates

Microclimates are very important to anyone with an interest in growing cold hardy tropical plants. A Microclimate is an area where the climate differs from the surrounding area. Microclimates can be very small such as the south side of a house or larger such as a densely built up city that has a different climate than the nearby countryside. Some Microclimate differences can be dramatic. New York City is a good example of an area with a very pronounced microclimate. New York City on the latest National Arbor Day Foundation Climate Zone Map is shown as Zone 8. The average minimum winter temperature in a zone 8 climate is 20-10 degrees Fahrenheit. This is the same climate zone as Atlanta Georgia.

Many species of subtropical plants can grow in a Zone 8 Climate. These include species of palms, many yuccas, Southern Magnolia’s, Crape Myrtle etc.
In New York City’s case there are several reasons for its warmer climate compared to other cities at a similar latitude such as Columbus Ohio or Indianapolis Indiana. The first is that New York City is at sea level. It will be several degrees warmer on average than a slightly higher city at the same latitude. The second reason is that it is surrounded by water. Water warms slowly and cools slowly compared to land. This means their summers will be slightly cooler and their winters slightly warmer than cities that are inland. The final reason for their warmer microclimates is the urban heat island effect. This happens when built up areas absorb and hold heat better than open countryside or forests. Other locations on the east coast can have warmer microclimates for similar reasons. Philadelphia, Cape Cod, Nantucket Island in Massachusetts and Block Island in Rhode Island all come to mind.

Picture of a Southern Magnolia in front of the Betsy Ross House in Philadelphia.
Picture of a Southern Magnolia in front of the Betsy Ross House in Philadelphia. The open courtyard around the tree is an example of a Microclimate.

You can use Microclimates to your advantage in growing cold hardy tropicals. The first example would be a south facing wall of a house. Another example would be a house on the side of a hill. The person living on the slope has less chance of late frost in the spring or early frost in the fall as opposed to the person down in the valley. This is because cold air is heavier and flows downhill. Other simple features can influence microclimates. An area right by a dryer vent can have soil that never freezes very deep even in the coldest of winters allowing plants such as Canna Lilies to survive much farther north than normal as the roots never freeze out. Growing up we had a large patch of Canna Liles surrounding our dryer vent. They were never dug up and survived the winter just fine. This was in an area of zone 6 winters. Normally Canna’s require zone 7-8 climates to survive the winter unprotected.

Microclimates can be created. Darker surfaces as generally warmer than lighter surfaces. Having black plastic mulch can raise soil temperatures by several degrees and in some cases protect lower growing plants from moderate frosts. Of Course the ultimate in creating your own Microclimates are various forms of winter protection such as cold frames and Greenhouses. I will touch on more of these types of winter protection in a future post.