Download Early November - 2014 - Louisiana Nursery and Landscape

LSU AgCenter
Ornamental Horticulture
E-News & Trial Garden Notes
Early November 2014
Nursery, Landscape & Garden Center Updates
Compiled by Allen Owings, Professor (Horticulture), Hammond Research Station, LSU AgCenter
Edited by Rick Bogren, Professor (Communications), LSU AgCenter
Phone 985-543-4125; Email [email protected]; www.lsuagcenter.com/hammond
Landscape News Articles (from Allen Owings and Rick Bogren)
Bed Preparation Key to Long-term Success – November 7
http://www.lsuagcenter.com/news_archive/2014/November/headline_news/Bedpreparation-key-to-longterm-landscape-success-.htm
Cold Protection in the Louisiana Landscape – Ornamentals and
Vegetables (from Dan Gill)
If you look around at some of our landscapes, particularly in south Louisiana, you would
think we live in the tropics. Indeed, some winters the temperature never does dip much
below the mid- to upper 20s, allowing tropicals to survive.
Despite the relative mildness of Louisiana winters overall, severe freezes do occur, and
they can be devastating to tropical plants growing in our landscapes. All it takes is one
night of temperatures in the low 20s or teens to severely damage or kill many tropicals.
Tropical and sub-tropical plants can be used effectively in the landscape, but they must
be protected or replaced when necessary. The best idea is to plant a good combination
of tender and hardy plants, so that your landscape is not totally devastated in the event
of extremely cold weather.
Although they are subject to cold damage or loss in winter, tropicals remain popular for
the colorful flowers, dramatic foliage and fragrance they bring to the summer landscape.
Nothing else performs as well as tropical plants during the intense heat of summer. But
using tropicals does mean that we sometimes need to help these plants to survive when
freezes do occur.
Hardy vs. Tender
Two terms are used when it comes to the ability of a plant to tolerate cold. If a plant will
endure temperatures below 32 degrees F with no damage, it is termed hardy. There are
degrees of hardiness. A plant that will tolerate a temperature of 15 degrees is hardier
than one that will be killed at temperatures below 25 degrees. Our commonly used
landscape plants, including trees, shrubs, ground covers, lawns and vines, are hardy to
at least 10 or 15 degrees and will not be damaged by typical winter weather.
Basically, a plant is considered hardy if it can reliably survive winter temperatures where
you garden with no protection or, at most, some mulch.
The term tender refers to plants that are killed or severely damaged by temperatures
below 32 degrees F. Surprisingly, many tropical plants are more cold-tolerant than we
give them credit for and will tolerate light freezes where the temperatures dip briefly
below freezing. But you do run a risk leaving them out or not covering them on nights
when even light freezes occur.
Many tropicals may survive a damaging freeze by coming back from their lower trunk,
crown, roots or below-ground parts (tubers, bulbs, rhizomes, corms). Since the ground
in Louisiana does not freeze, plant parts at or below the soil surface typically survive –
and this allows these plants to be considered hardy.
Basically, a plant is considered tender when it will not reliably survive winter
temperatures where you garden without extensive protection.
Types of Freezes
When freezes do come, they can be characterized as radiational or advective.
Radiational freezes or frosts occur on calm, clear nights when heat radiates from
surfaces of objects into the environment. These freezes are generally considered light
and primarily damage the foliage of tropicals. Plant damage from a radiational freeze
can be minimized by reducing radiant heat loss from plants by covering them.
Advective freezes occur when cold air masses move down from northern regions,
causing a drastic drop in temperature. Windy conditions are normal during advective
freezes. Although radiant heat loss also occurs during an advective freeze, the
conditions are quite different from a radiational freeze. The temperatures tend to be
much lower and are liable to last longer during advective freezes, and protecting
tropicals is more difficult.
Freeze Terms
What happens without protection
Frost – temperatures around 30 to 32 degrees
(little or no damage)
Light freeze – 28 to 30 degrees
(light damage mostly to foliage)
Hard freeze – mid-20s
(kills more tender tropicals, substantial damage to others)
Severe freeze – low 20s
(major damage or death to virtually all tropicals)
Catastrophic freeze – teens
(death to most tropicals)
Factors Affecting Cold Injury
The most important factors in how much damage a plant receives from cold are how
hardy it is and how cold it gets. There are, however, a surprising number of other factors
that can play a big role in how much cold injury actually occurs.
Make sure good care is given to your landscape during the summer growing season.
Plants, even hardy ones, doing poorly or in low vigor are more susceptible to cold
damage. Pruning and fertilizing hardy trees, shrubs and ground covers should be
avoided after September, as this can stimulate late growth which is not as cold-hardy
and may lead to freeze injury.
A sudden drop to below-freezing temperatures from a period of relatively mild weather
may cause damage even to hardy plants that might otherwise have suffered little or no
damage. A gradual decrease in temperature over a period of time will harden off plants,
allowing them to withstand freezing temperatures better. This is not true for especially
tender tropical plants, as they will not tolerate freezing temperatures regardless of the
preceding temperatures.
The longer below-freezing temperature persist, the more likely damage will occur. This
is because as time goes by, heat stored in plants, soil, walls, etc. that initially moderates
temperatures around the plant is lost. Freezes that last 8 hours or more are particularly
damaging to tender plants.
Where a tropical plant is located in the landscape can make a big difference in how
much damage occurs. The careful placement of tender or less-hardy plants in sheltered
areas that block cold north winds and trap the heat of the sun can help them survive
freezes. Planting in areas covered with overhangs or tree canopies will also help to
minimize cold damage.
Finally, plants do not “feel” wind chill. Do not focus on wind chill temperatures – it is the
actual temperature you need to pay attention to.
What to Do Before a Freeze
WATER
If the soil is dry, thoroughly watering landscape plants before a freeze may help them
better deal with the cold. Cold weather is often accompanied by strong, dry winds.
These winds may cause damage by drying plants out, and watering helps to prevent
this.
Wetting the foliage of plants before a freeze does not, however, provide any cold
protection. Neither will a layer of ice protect plants once the water is turned off. A spray
of water must continue through the entire freezing period for it to provide protection.
MOVE INSIDE
Move all tender plants in containers and hanging baskets into buildings where the
temperature will stay above freezing. If this is not possible, group all container plants in
a protected area (like the inside corner of a covered patio) and cover them with plastic.
If plants are kept inside for extended periods, make sure they receive as much light as
possible.
MULCH
For plants growing in the ground, mulches can help protect them. Use a loose, dry
material such as pine straw or leaves. Mulches will only protect what they cover. Mulch
at the base of a bird-of-paradise will help the roots but will provide no added protection
to the leaves. Mulches, then, are best used to protect below-ground parts or crowns or
may be used to completely cover low-growing plants to a depth of 4 inches. Leave
mulch that completely covers plants in place no more than three or four days. Mulch at
the base of a plant can remain in place all winter.
COVER
If they are not too large, individual plants can be protected by covering them with
various-sized cardboard or Styrofoam boxes.
Larger plants can be protected by covering them with fabric or plastic. Fabric coverings,
such as sheets, can get wet and heavy if rains occur. Plastic would be better in rainy
weather. However, wherever a leaf touches a plastic cover, it will freeze. Both of these
issues can be resolved by providing simple supports under the cover to support wet
fabric or keep a plastic cover from contacting the foliage. The structure holds the
covering off the foliage, preventing branch breakage and improving cold protection. It
need be nothing more elaborate than three stakes slightly taller than the plant driven
into the ground. The cover should extend to the ground and be sealed with soil, stones
or bricks. Clear plastic covers should be vented or removed on sunny, warm days.
The covers will work best for radiational freezes by preventing or blocking heat loss.
The extreme, prolonged cold that occurs during advective freezes is not so easily dealt
with. Many plants will still die even with protection. This can be helped by providing a
heat source under the covering. A safe, easy way to do this is to generously wrap or
drape the plant with small outdoor Christmas lights (not LED lights). The lights provide
heat but do not get hot enough to burn the plant or cover. Please be careful and use
only outdoor extension cords and sockets.
If necessary, you may prune back a large plant, like a hibiscus, to make its size more
practical to cover. For trees, such as palms and citrus, that are too large to cover, you
may at least want to wrap the trunk with an insulating material such as foam rubber or
blankets. Even if the top dies, you may be able to regrow the tree from the surviving
trunk. For palms, the trunk must be wrapped from ground level to the base of the leaves
to protect the trunk and crown.
If you are growing vegetables, harvest any broccoli, cauliflower, fava beans or peas that
are ready. Freezing temperatures will not hurt the plants but can damage the heads,
pods and flowers. Also, any ripe citrus fruit should be harvested prior to a hard freeze.
What to Do After a Freeze
Unless you are keeping them inside for the rest of the winter, move container plants
back to their spots outside. Plants do not mind being moved in and out as needed
through the winter.
For plants that you covered, remove or vent clear plastic covers on plants to prevent
excessive heat buildup if the next day is sunny and mild. You do not need to completely
remove the cover if it will freeze again the next night. You may leave plants covered
with blankets, sheets or black plastic for several days without harming them, but
eventually the covers will need to be removed so they can get light.
Do not prune anything for a week or more after a freeze. It often takes a week or so for
all of the damage to become evident.
Damaged growth on herbaceous or non-woody tropical plants, such as cannas,
elephant ears, birds-of-paradise, begonias, impatiens, philodendron and gingers, may
be pruned away back to living tissue. This pruning is optional and is done more to
neaten things up than to benefit the plants. However, if the damaged tissue is oozy,
mushy, slimy and foul smelling, it should be removed.
If you don’t prune before, be sure to cut back or prune these herbaceous tropicals in
spring after danger of freezes is past and before they make substantial new growth.
You may remove the damaged foliage from banana trees, but do not cut back the trunk
unless you can tell for sure that it has been killed. It will look brown, feel mushy, feel
loose in the soil and bleed a lot if punctured. The exception would be any banana trees
that produced a bunch of fruit last year. They will not send up any more new growth and
should be cut to the ground to make room for new shoots that will come up this
summer.
Generally, it’s a good idea to delay hard pruning of woody tropical plants, such as
hibiscus, tibouchina, angel trumpet, croton, ixora, schefflera, copper plant and rubber
tree, until new growth begins in the spring and you can more accurately determine
which parts are alive and what is dead. Dead leaves on woody tropical plants can be
picked off to make things look neater. If you can clearly determine which branches are
dead on a woody plant, you can prune them back. Try scratching the bark with your
thumbnail. If the tissue underneath is green, it’s still alive. If the tissue is tan or brown,
the branch is dead. Start at the top and work your way down to see how far back the
plant was killed.
Cold Tolerance of Commonly Grown Plants
These temperatures are cautious. You may find plants will take several more degrees of
cold than indicated in the chart. But to absolutely prevent damage, take action to protect
or bring inside when these temperatures are predicted.
Plants will often return from their crowns, roots or below ground parts (bulb, rhizome,
tuber, corm) if frozen back.
Plant
Agapanthus * (Agapanthus)
Agave * (Agave americana)
Allamanda (Allamanda cathartica)
Aloe (Aloe vera)
Amaryllis * (Hippeastrum)
Angel's Trumpet * (Brugmansia)
Ardisia * (Ardisia japonica, A. crenata)
Areca Palm (Dypsis lutescens)
Asparagus Fern * (Asparagus species)
Azaleas * (Rhododendron cultivars)
Banana * (Musa, hardiness depends on species)
Bamboos* (hardiness depends on species)
Bird of Paradise * (Strelitzia reginae)
Blue Daze (Evolvulus glomeratus)
Boston Fern * (Nephrolepis exaltata)
Bottle Brush Bush (Callistemon rigidus)
Bougainvillea (Bougainvillea)
Yesterday-Today-Tomorrow* (Brunfelsia)
Butterfly Vine * (Mascagnia macroptera)
Canna Lily *(Canna)
Temperature plant may be damaged
or killed
23 to 15degrees or below
23 to 15 degrees or below
32 to 28 degrees or below
28 to 23 degrees or below
28 to 23 degrees or below
28 to 23 degrees or below
23 to 15 degrees or below
32 to 28 degrees or below
25 to 23 degrees or below
16 to 10 degrees or below
32 to 28 degrees or below
28 to 23 degrees or below
25 to 23 degrees or below
32 to 28 degrees or below
28 to 23 degrees or below
23 to 15 degrees or below
32 to 23 degrees or below
25 to 23 degrees or below
25 to 23 degrees or below
30 to 28 degrees or below
Temperature plant may be damaged
or killed
Camphor Tree * (Cinnamomum camphora)
23 to 15 degrees or below
Carissa (Carissa grandiflora)
28 to 23 degrees or below
Cassava * (Manihot esculenta)
32 to 30 degrees or below
Cassia * (Cassia [Senna] species; hardiness varies)
25 to 23 degrees or below
Castor Bean (Ricinus communis)
32 to 28 degrees or below
Chinese Fan Palm (Livistona chinensis)
20 to 15 degrees or below
Rice Paper Plant* (Tetrapanax papyriferus)
25 to 23 degrees or below
Citrus (hardiness varies depending on type)
25 to 15 degrees or below
Clerodendrum* (hardiness varies depending on species) 28 to 23 degrees or below
Clivia * (Clivia miniata)
30 to 28 degrees or below
Queen Palm (Syagrus romanzoffiana)
23 to 15 degrees or below
Coleus (Solenostemon scutellarioides)
32 to 28 degrees or below
Confederate Jasmine* (Trachelospermum jasminoides) 23 to 15 degrees or below
Copper Leaf* (Acalypha wilkesiana)
30 to 28 degrees or below
Croton (Codiaeum variegatum)
30 to 28 degrees or below
Crybaby Tree * (Erythrina crista-galli)
25 to 20 degrees or below
Date Palm (Phoenix dactylifera)
20 to 15 degrees or below
Dracaenas (Dracaena species and cultivars)
30 to 28 degrees or below
Duranta* (Duranta erecta)
28 to 23 degrees or below
Elephant Ears* (Colocasia esculenta; Alocasia)
32 to 28 degrees or below
Eucalyptus* (Eucalyptus cineraria)
23 to 15 degrees or below
Fatsia* (Fatsia japonica)
23 to 15 degrees or below
Fig Vine* (Ficus repens)
23 to 15 degrees or below
Gerbera Daisy* (
28 to 23 degrees or below
Gingers* (many are root hardy)
30 to 28 degrees or below
Golden Rain Tree* (Koelreuteria bipinnata)
20 to 10 degrees or below
Hibiscus* (Hibiscus rosa-sinensis)
27 to 23 degrees or below
Impatiens (Impatiens walleriana)
32 to 28 degrees or below
Ixora (Ixora coccinea)
32 to 28 degrees or below
Jelly Palm (Butia capitata)
20 to 15 degrees or below
Lady Palm* (Rhapis excels)
20 to 10 degrees
Lantana* (Lantana camara)
28 to 23 degrees or below
Mandevilla (Mandevilla)
32 to 28 degrees or below
Mediterranean Fan Palm* (Chamaerops humilis)
20 to 15 degrees or below
Mexican Heather* (Cuphea hyssopifolia)
28 to 23 degrees or below
Night-blooming Jasmine *(Cestrum nocturnum)
28 to 23 degrees or below
Norfolk Island Pine (Araucaria heterophylla)
25 to 23 degrees or below
Oleander* (Nerium oleander)
20 to 15 degrees or below
Orchid Tree* (Bauhinia species)
28 to 23 degrees or below
Papaya* (Carica papaya)
30 to 28 degrees or below
Passion Vine* (Passiflora species and hybrids)
28 to 23 degrees or below
Periwinkle (Catharanthus roseus)
32 to 28 degrees or below
Split-leaf Philodendron* (Philodendron bipinnatifidum) 32 to 28 degrees or below
Plumbago* (Plumbago auriculata)
25 to 23 degrees or below
Poinsettia *(Euphorbia pulcherrima)
30 to 28 degrees or below
Primrose Jasmine *(Jasminum mesnyi)
23 to 15 degrees or below
Rangoon Creeper* (Quisqualis indica)
30 to 25 degrees or below
Rosemary (Rosmarinus officinalis)
20 to 15 degrees or below
Plant
Temperature plant may be damaged
or killed
Rubber Plant *(Ficus elastica)
28 to 23 degrees or below
Sago Palm *(Cycas revoluta)
20 to 15 degrees or below
Schefflera (Schefflera arboricola, S. actinophylla)
30 to 25 degrees or below
Shrimp Plant *(Justicia brandegeeana)
28 to 23 degrees or below
Spineless Yucca* (Yucca elephantipes)
23 to 20 degrees or below
Spider Plant *(Chlorophytum comosum)
28 to 23 degrees or below
Sweet Olive (Osmanthus fragrans)
20 to 15 degrees or below
Sweet Viburnum* (Viburnum odoratissimum)
20 to 15 degrees or below
Umbrella Plant *(Cyperus alternifolius)
25 to 23 degrees or below
Viburnum* (Viburnum suspensum)
23 to 15 degrees or below
Walking Iris* (Neomarica gracilis)
28 to 23 degrees or below
Walking Iris, Blue* (Neomarica caerulea)
25 to 20 degrees or below
Washingtonia Palm (Washingtonia robusta)
20 to 15 degrees or below
Wax Leaf Begonia (Begonia semperflorens-cultorum) 30 to 25 degrees or below
Wedelia *(Wedelia trilobata [Sphagneticola trilobata]) 28 to 23 degrees or below
Weeping Fig (Ficus benjamina)
30 to 28 degrees or below
Plant
* Plants will often return from their crowns, roots or below ground parts (bulb, rhizome, tuber,
corm) if frozen back.
Cold Protection for Winter Vegetables
Although winter vegetables are generally hardy, new plantings may need to be
protected from hard freezes as will certain vegetables near or at harvest stage. If
temperatures are predicted below 30 degrees F, young seedlings should be covered
with a layer of loose mulch, sheets or tarps. The cover may remain over the plants for a
few days, but remove it as soon as the freezing episode is over.
Even though the plants are hardy into the teens, broccoli and cauliflower heads are
tender. Also, the leaves of lettuce and the leaves, flowers and pods of peas may be
damaged by hard freezes in the mid- to low 20s. Although protection with covers is an
option, the gardener should consider harvesting all mature and nearly mature produce
before a major freeze.
The following lists will give you a quick guide to the ability of some vegetables to endure
freezes. Remember that such factors as the age of the plant, prior weather conditions
and the location of the plants are also factors in addition to the temperatures.
Less Hardy
Protect or harvest if temperatures are predicted to go below the mid- to upper 20s: fava
beans, broccoli heads ready to harvest, cauliflower heads ready to harvest, lettuce and
peas.
Moderately Hardy
Will tolerate temperatures down to the mid- to low 20s with little or no damage: Swiss
chard, Chinese cabbage, kohlrabi, mustard, spinach, radishes and turnips.
Very Hardy
Will survive temperatures in the low 20s and teens: beets, Brussels sprouts, carrots,
celery, collards, garlic, onions, parsley, leeks and shallots.
Louisiana Super Plants – 2015 (from Allen Owings)
Citrus and Cold Weather (from Alan Vaughn and Dan Gill)
Louisiana has its coldest temperatures in January, but freezes can begin as early as
November and occur well into early March (sometimes later). Protection of citrus trees
becomes important when severe freezes occur. It is difficult to pin point a "threshold"
temperature at which it becomes necessary to protect citrus trees. The biggest difficulty
in making such a determination is the difference between various types of citrus in their
tolerance of cold.
Satsumas, for example, do not need protection until the temperatures approach 20
degrees F. Lemons, limes and oranges generally need to be protected when the
temperature dips below 26 degrees F. However, theses trees may be killed or damaged
at these temperatures if they are not sufficiently hardened with enough pre-conditioning
cold temperatures to halt their growth.
The length of time citrus trees are exposed to sub-freezing temperatures is also
significant. Exposure to sub-freezing temperatures for more than 24 to 36 hours can be
devastating. But if the temperatures moderate to above freezing prior to this time,
damage is usually light.
All ripe fruit should be harvested from trees prior to a significant freeze. Temperatures
cold enough to damage the tree will also ruin the fruit. It takes temperatures in the midto low 20s five to 10 hours to freeze the fruit.
Three factors are basically involved in determining freeze susceptibility of citrus trees:
1) The type and age of the citrus. Satsumas are the most cold-hardy of the commonly
grown citrus species in Louisiana. Kumquats follow with just a slight less amount of cold
hardiness. In order from most cold-hardy to least cold-hardy: satsuma, kumquat,
orange, grapefruit, lemon and lime.
A citrus tree increases in hardiness as it gets older. Trees with larger, denser canopies
deal with the cold better because they trap more heat.
2) Threshold temperatures are approximately 20 degrees for satsumas and kumquats
and about 26 degrees for all other citrus.
3) The duration of the sub-freezing temperature is very significant. If the temperature is
below freezing for 24 to 36 hours, damage can usually be expected.
Generally, when freeze injury occurs, damage is inflicted mostly to cell membranes by
freezing and thawing. The least cold-hardy tissues of citrus trees are new buds, flowers
and small fruit. The more cold-hardy part of the tree is the mature wood of major
branches and the trunk.
If a citrus tree is gradually exposed to cooler temperatures, a process called hardening
occurs and trees become more tolerant to freezing temperatures. Citrus trees are
evergreen and never become full dormant, but trees that are slightly dormant (preconditioned by gradual cold) are less likely to be damaged by cold. So, chilly but abovefreezing nights (30s and 40s) that occur during fall and early winter before major freezes
make the trees more cold tolerant. Severe freezes taking place when only mild weather
has occurred previously are more likely to cause significant damage.
The best way to lessen cold damage to citrus is to maintain healthy trees. Cultural
practices that tend to induce and maintain dormancy in winter should be used. These
methods include no late-summer or fall fertilization or pruning. Vigorous trees may
recover from cold injury. Weak trees that are showing disease, insect damage or
nutritional deficiencies are the ones most severely damaged and are the slowest to
recover after freezes.
Seven steps are suggested to reduce freeze damage:
1) Clean cultivation under the canopy of a tree, mechanically or by herbicides, prior to
winter is recommended. Grass, weeds and straw mulches prevent heat from entering
the soil during the day; therefore, less heat energy is stored in the soil under the tree for
release at night.
2) For trees too large to cover, banking the lower trunks with soil or using tree wraps of
bubble wrap, foam rubber or Styrofoam will help prevent cold damage to the trunk. This
must be done before the first killing freeze and can be left on through the winter. Trunks
should be treated with a copper fungicide before wrapping or banking to prevent root
rot. Or the coverings may be applied during freezes and removed during mild weather.
Although tree tops may still be lost during freezes, a tree can recover if its trunk and root
system are intact. Banking or wraps should be removed in the spring.
3) If the weather has been dry, several days in advance of a cold front the soil beneath
citrus trees can be irrigated. Good soil moisture acts as a cold buffer, and trees that are
drought stressed may experience more cold damage. This must be done well in
advance of the freeze. If this is done at the time the front arrives, evaporation may occur
and result in colder temperatures near the tree.
4) If pruning is needed, it should be done in spring to allow tree growth to mature before
winter. Do not prune in late summer or fall. Cuts should be made at branch crotches
leaving no stubs. Prune to maintain a full, dense canopy. Trees need good leaf
canopies to cut wind speed through the canopy and reduce the rate of cooling. Leaves
radiate heat to each other. Outer leaves may be lost to a freeze, but complete loss of
inner leaves is averted by a thick canopy.
5) Fertilizer should be applied to citrus trees in late January or early February. A
complete fertilizer such as 8-8-8 at the rate of two pounds per year of tree age may be
used. Stop increasing the rate when you reach 15 pounds. If using 13-13-13, the rate is
one and one-half pounds of fertilizer per year of tree age. Stop increasing the rate when
you reach 10 pounds. Spread the fertilizer around the edge of the branches in the area
of the feeder roots. Apply a subsequent application of nitrogen when good soil moisture
exists in June. Late-summer or fall applications of fertilizer should be avoided as they
can reduce the hardiness.
6) Oil sprays used to control insects and mites decrease cold tolerance and should not
be used later than August 15.
7) To protect a single smaller tree, construct a simple frame over trees and encase the
tree with one or two layers of translucent plastic. This is generally most practical for
smaller trees. In southeast Louisiana, such an extreme practice would be needed only
on a few severely cold nights.
Before covering, the tree could be generously draped and wrapped with small, outdoor
incandescent Christmas lights to provide additional warmth and increase the level of
protection. Incandescent Christmas lights will not damage the tree even if they come
into contact with it.
The frame and cover can stay in place indefinitely but will need to be vented. Air
temperatures within should not be allowed to go above 85 degrees to 90 degrees F.
Venting should be provided on sunny, warm days to prevent overheating and to
maintain a supply of fresh air.
LSU AgCenter Plant Diagnostic Clinic
LSU AgCenter Soil Testing and Plant Analysis Lab