Gardening Questions

Q: How do I protect my plants from winter freezes?

When the year becomes the season of witches and goblins, quickly becoming the season of turkeys and pumpkin pies, growers of tropical and semi-tropical plants, begin planning for early frosts and winter freezes.  The spring is often a time of mushy brown leaves, burnt foliage and twigs, split bark and damaged fruit, so early planning is a must.

We will begin this article by explaining how plants turn into those mushy messes after a freeze. Explained very simply, when the temperatures begin to drop, foliage and fruit will begin to lose their heat.  The water inside a plant freezes causing ice crystals to form.  These crystals break the plant’s cell walls. When the temperature warms the cells lose their fluids, die and turn to mush.

Our most common challenge is the marginal freeze.  This only lasts a few hours with temperatures dropping to below freezing in the early morning hours, then back up above freezing by mid-morning. This is a quick temperature change, not too unpleasant but enough to kill any buds or blooms on fruit trees.  By planning ahead, we can do a lot to protect our plants.  Additionally, the less wind involved, the more effective our efforts.

Our most dreaded challenge is the “Nor’easter” that blows in a few times each winter.  It is usually accompanied by high winds, rapidly falling temperatures and rain or sleet. There is little we can do beyond moving plants into a greenhouse or garage. Most plants will suffer enough damage to set back production by a few years.  But, there are strategies we can use to at least keep the plant alive.

Site Selection

The first step in freeze protection is the initial site selection.  All tropical and semitropical plants should be planted on the south side of a windbreak.  This can be a fence, house, garage, shed or hedge. The windbreak will block much of the north wind and absorb heat throughout the day, releasing it during the night.

CoveringGraphic to show correct tenting

Tent the plant to trap heat and prevent radiation to a clear sky.  This could be plastic, sheets, tarps, or blankets.  You can also use large cardboard boxes, trash cans or build a frame of wood, covering it with cloth or plastic.  Of course, wind is going to be a problem so anchor your tent with bricks, lumber, buckets of water, or stakes.  When tenting, remember to use the covering like a tent.  It should cover the plant with the ends dropping to the ground.  It is not helpful to wrap the plant like a lollipop.  This method does not take advantage of the radiant heat coming upward from the ground.  The tent method will capture this heat and help you plant survive the freeze.

You can add additional protection by raking the mulch away from the plant.  Bare ground absorbs the sun’s heat while mulch will deflect the heat.  Another source of heat is lighting.  Add strands of the old-style Christmas lights, the new twinkly ones will not add heat.  A mechanics light, or bathroom heater will also work.  Do be careful with these last two so you don’t awake to flames in the backyard.

Water

When a big freeze is predicted, probably the last thing you think of is getting out to water the plants.  Seems counter-intuitive but water can protect plants. Plants suffering from drought are less tolerant of cold and suffer injury at warmer temperatures than normal.  Water plants several days ahead of cold weather.  Secondly, water absorbs heat from the sun, stores it, then releases the warmth slowly.  Watering before a freeze creates a source of warmth higher that the freezing point that will radiate through the night.  This alone will not save your tree but used in conjunction with tenting you should have good results.

Another method is using large trash cans or 5-gallon buckets filled with water.  Make sure the lid is on, this helps with radiation.  If you have a grafted plant, place several buckets of water around the truck to protect the graft union.  Along with tenting, this has proven to be a reliable method of saving the plant.

Another use of water is spray irrigation during the freeze.  You have probably seen fruit growers using irrigation to protect crops from a frost or freeze. For the homeowner, this method seldom works and often make things worse. The plants must be showered with a water spray from before the freeze but during the freeze and well after the freeze.  A homeowner’s irrigation system release too much water for this method.  For homeowners, this results in a soggy, muddy lawn with drowned plants.  The recovery is long and damaging.

Banking

Banking soil up the trunk of grafted trees is beneficial in saving tree grafts.  Covering the graft union will act like insulator.  You may lose the branches and leaves but the tree will regrow true to the scion you purchased.  Be sure to use soil, not mulch or leaves.  Only soil will provide the protection you need and aid in the radiant heat process.  To use this method, spray the trunk with a fungicide first.  Then bank soil all around the trunk and up beyond the graft union.  You can do this in November or with the first predicted freeze and leave until March.  After removing the soil bank from the trunk, spray again with a fungicide.  Also, make sure to remove the soil from around the roots.  Citrus roots are very shallow and will suffer if they become too deep.

Insulation

InsulationCovering plants is accomplished by using various objects to keep ice from forming in the cells of the woody parts of plants.  The use of pipe insulation, sheets, Styrofoam or plastic give spotty results and simply do not work well.  However, sheets of fiberglass insulation will work to protect from freezes.  You will need to wrap the plants prior to the freeze and remove as soon as the freeze has passed.  Otherwise the plant will overheat.  It is helpful to cover the insulation with plastic to keep dry.

Whichever method you use, the devil is in the details.  When it comes to freeze protection it’s all in the timing.  A sudden 30-degree drop will cause severe damage no matter the precautions you take.  A gradual cooling off may do no damage.  But, if a spring crop is important, you should have a plan in mind for winter protection.  Have your materials on hand and don’t wait until the “Nor’easter” is upon us…prepare as soon as it’s predicted.


Aster Yellow Disease

Q: Have you seen this in your garden?

If you see this, you may have Aster Yellows in your garden. Aster Yellows has been showing up in gardens around the county.  Click here to find out more about Aster Yellows and what to do if you have this on a plant in your yard.


Q: A freeze is predicted for this week.  Should I harvest my lemons now?

A: Predictions are often incorrect so it is best to wait before harvesting all your citrus.  Fruit freezes if the temperatures drops to 26-28 degrees for several hours.  With temperatures of 32 you may have foliage damage but the fruit will be fine left on the tree.  Learn more at https://aggie-horticulture.tamu.edu/newsletters/hortupdate/2011/mar/citrus_freeze.html


Q:Wooly aphids on a dwarf peach tree.  I have white powdery stuff on my dwarf peach tree. What can I do?

A:  The problem you see on your dwarf peach is woolly aphids.  Woolly aphids are tenacious little creatures but can be treated effectively with low-impact methods of control.  These aphids are a mixture eggs, larva, juvenile and adults.  The good news is they have lost their wings and cannot fly away.  Normally, we would suggest you leave them for nature to take care of but this is a huge infestation so it’s time to take measures to knock down their numbers.

The first action should be to take a cloth or simply put on a glove and wipe the majority off the limb and twigs.  Secondly, use a strong blast of water to wash as many off as possible.  Be sure to spray the trunk, limbs, twigs and under leaves.  This should remove the majority of aphids.  You can now decide to leave them to predators or take further action.  If you decide to continue, you should use a horticulture oil such as Neem oil.  Mix it as directed and follow the instructions on the bottle.  The purpose of the oil is to smother the remaining aphids and any eggs that may hatch.  Saturate under the leaves and in all the nooks and crannies of the trunk.  Should they reappear, just repeat these steps.  Most likely, some aphids will be able to overwinter on the plant so be prepared to use these methods in the spring.


Bark lice webbing on oak

Q:  I looked out at my lawn this morning and saw this shiny, gauzy white web all over my trees?  How can I remove it? Is it harmful? 

A:  Well, you are the lucky winner of the Bark lice Lottery.  We have two types of bark lice in this area, Archipsocus nomas and Cerastipsocus venosus.  Both are small soft bodied insects, rarely seen.  They are often referred to as tree cattle because they herd together as they feed around the tree truck and limbs.  They are rarely found on the foliage.  Bark lice are a great clean-up crew feeding on fungi, bacteria, dead insects and lichens.

Although some think they are unsightly, they are highly beneficial and should be left alone.  Eggs are laid under the protective web, the insect then goes through five to six instars.  With the first fall frosts, the group will begin to decline, along with the web.


Sooty Mold Q:  What is this black stuff on my lemon tree leaves?  How do I get rid of it?

A:  What you have on your leaves and fruit is black sooty mold.   We have a number of people complaining of sooty mold this year because we had a cool, mild, wet winter followed by high heat and humidity.  Perfect growing conditions.

Sooty molds are fungi growing and feeding on honeydew.  Honeydew is produced by sap sucking insects feeding on your plant.  These insects include white fly, scale, meaylbug, psyllids, aphids, just to name a few.  It is important to deal with the insect as well as the sooty mold.

Sooty mold can be a real problem for plants by restricting the sun’s ability to penetrate to the leaf reducing the plant’s ability to perform photosynthesis.  This reduces tree vigor and can result in leaf and fruit drop.

First step is to identify the insect.  Should it be scale or aphids, look for fire ants at the bottom or near to the tree trunk.  Fire ants will farm the insect in order to harvest and eat the honeydew.  You must control both the sap sucking insect and the ants.

Non-chemical control of the insects will be difficult but not impossible.  Do hit the foliage with a hard water spray early in the morning for several days and then several times a week thereafter.  You can also use an insecticidal soap but only if you don’t see any beneficial insects such as lady bugs or predators such as lizards.  A dormant oil can be used to suffocate the insects if the temperature is under 85 degrees.

Purchase a good fire ant poison and use as directed.  Should you need to use a chemical for insect management, do read the label, make sure it includes control of the insect you are targeting, then use as instructed.


Oak Leaf BlisterQ:  My oak tree is dropping leaves and looking bad.  What can I do? 

A:  It appears you have Oak Leaf Blister. This is a fungal disease that attacks most all varieties of oak .  Although the symptoms may begin after a cool, wet spring, most homeowners don’t notice the problem until leaves begin prematurely falling in late summer.  New leaves may have blisters and lesions while older leaves just look dry and blistered.

A good regimen of fertilization and watering will enhance tree vigor throughout the year.  It is useless to spray the tree unless you’ve had repeated years of symptoms.  In this case, you can spray the tree with a dormant oil before bud break in early spring.  Additionally, remove all fallen leaves and destroy to minimize reinfection.  If this is not possible, mow the leaves repeatedly then add a nitrogen fertilizer to add in a quick breakdown.

 

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