The Garden Professors™

In this edition of P&P we’ll be exploring the life of the “Father of Texas Botany”, Ferdinand Jacob Lindheimer.

On May 21, 1801, Herr and Frau Lindheimer of Frankfurt, Germany welcomed little blue-eyed Ferdinand to the family. After schooling at the Frankfurt Gymnasium and a Berlin prep school, Ferdinand spent the next 30 years studying at universities in Bonn, Jena, and Wiesbaden.

In 1833, for political reasons, Ferdinand decided it was best for him to leave Germany. By 1834 he was in Belleville, Illinois. Not finding Belleville to his liking, he caught a boat down the Mississippi to New Orleans, LA.

After some time he and a few companions tried to go to Texas. But the Texas revolution was heating up and they wound up being sidetracked to Mexico, eventually winding up in Veracruz. There he worked on a banana plantation for over a year all the while becoming infatuated with the regional flora and fauna. But he still wanted to go to Texas and left Mexico just as the hostilities in Texas were escalating. In an effort to reach Texas he tried joining the Texas revolutionaries but alas, it was not to be. He wound up ship-wrecked on the Alabama coast near Mobile.

So close and yet, so far.

Being the headstrong German that he was, he tried once again to reach Texas and finally arrived at San Jacinto (pronounced Hah-seen-toe) the day AFTER the final battle of the Texas Revolution on April 22, 1836. Despite missing most of the action he joined the army of the new Republic of Texas and served 19 months. During this time and after his discharge in 1837 he spent any free time exploring the flora of his new home.

An old friend from Frankfurt, Georg Engelmann, invited Lindheimer to spend the winters of 1839–40 and 1842–43 with him in St. Louis. (Englemann had immigrated to America in 1832 and dabbled in botany as a hobby.) Lindheimer brought preserved Texas plant samples with him on these visits. Via their friendship Lindheimer’s collections came to the attention of professor Asa Gray, founder of the Gray Herbarium at Harvard University and author of the original Gray’s Manual of the Botany of the Northern United States. The plants from the Republic of Texas generated quite a bit of excitement in old Harvard Yard.

In 1843 arrangements were made for Lindheimer to collect plant specimens for Engelmann and Gray. He spent the next nine years collecting from a variety of Texas areas, including Chocolate Bayou, Cat Springs, Matagorda Bay, Indianola, and Comanche Springs. 

Over the next thirteen years, Lindheimer collected over fifteen hundred species in central and south Texas for Engelmann, Gray and others who were building collections. The samples had to be pressed and dried with multiple changes of blotting paper, then mounted and shipped. The collection date, location and habitat were logged for each specimen. Lindheimer earned $8 for each hundred specimens submitted. Occasionally he sent seeds or cuttings so Gray could try propagating the plants at Harvard. Using his own knowledge and whatever reference materials he could find, Lindheimer could place most plants in the appropriate family and make a good guess at the genus. But official classification was left to the scholars who received his samples.

In 1844 Lindheimer was granted land on the Comal River in the new community of New Braunfels, TX. and remained in the area for the rest of his life. He kept collecting, started a botanical garden, and in 1852 was elected the editor for the town newspaper, Neu Braunfelser Zeitung, one of the earliest newspapers in Texas. He was associated with the paper for the next 20 years, eventually becoming the publisher. Legend is that it never missed an issue, not even during the Civil War when newsprint was not to be had. Lindheimer printed on butcher paper, wrapping paper, and leftover paper from his plant-preserving supplies.

In 1872 Lindheimer ended his association with the paper to devote more time to his work as a naturalist. He is credited with discovering several hundred plant species and his name is used to designate forty eight species and subspecies of plants and one species of snake. ( I really wanted to put a picture of the snake here but was advised that some people don’t like reptiles as much as I do. Sigh)

In 1879 his essays and memoirs were published under the title Aufsätze und Abhandlungen.

Lindheimer died on December 2, 1879, and was buried in New Braunfels. His grave is registered on The Historical Marker Database and his house on Comal Street in New Braunfels, is a museum, a Registered Texas Historic Landmark and is on the National Register of Historic Places.

Lindheimer’s plant collections can be found in at least twenty institutions, including the Missouri Botanical Gardens, the British Museum, the Durand Herbarium and Museum of Natural History in Paris, the Harvard University Herbaria, the Smithsonian Institution, and the Komarov Botanic Institute in St. Petersburg

Want to learn more about Ferdinand Lindheimer?

https://biodiversity.utexas.edu/news/entry/the-father-of-texas-botany#:~:text=Many%20species%20in%20central%20Texas,shows%20up%20in%20people%27s%20houses.

https://www.tamupress.com/book/9781623498764/the-writings-of-ferdinand-lindheimer/

https://www.tamupress.com/book/9781585440214/life-among-the-texas-flora/

https://archive.org/details/mobot31753003757678

I saw an article describing an atmospheric phenomenon called the “pneumonia front” this week and it made me start thinking about local kinds of wind and their names. No matter where you live, in the United States or elsewhere in the world, you have wind patterns that are related to your local geography. These winds can affect gardens, especially if they are persistent over time, but I enjoy hearing about the different names for wind too.

What causes the wind to blow?

Wind is the movement of air from one place to another. The air movement is driven by differences in air pressure from one place to another—the atmosphere tries to even out the pressure so air molecules are always moving from areas with higher density and pressure to areas with lower density and pressure. Since density and pressure are related to temperature (remember your ideal gas law from high school chemistry?) and temperature frequently changes as the sun moves across the sky or lakes and oceans warm and cool, the air is nearly always moving except where there is locally no variation in pressure such as the center of a high-pressure area.

Two common types of local winds

Winds are often linked to specific geographic features. For example, sea or lake breezes are located along the shores of large water bodies and are driven by pressure differences related to the relative temperatures of the land and water. When the water is colder than the land (for example, on a hot summer day), air pressure over the hot land is lower than over the cold water due to rising air over land (you can often see clouds where this is occurring). Air from over the water blows onshore in response to the lower pressure on land, leading to a cool breeze flowing over the hot land, cooling things off. At night when the land cools off more quickly than the water, the flow reverses and becomes a land breeze. Monsoons like the ones in India, the Southwest US, and other places are the largest-scale version of a sea breeze over thousands of miles and develop over weeks instead of hours.

Another geography-linked local wind is the katabatic wind. Katabatic winds are related to differences in elevation that cause temperature variations that result in density differences in the air. In a katabatic wind, air at upper elevations cools off at night, creating a pool of very dense air that rushes down the sides of the mountains to pool in the valleys, creating pockets of very cold air. Vineyard owners know this and plant vines on the sides of hills so that the vines are not exposed to the coldest air (and to take advantage of sunlight, too). The recent frost in New England caused severe losses of apple blossoms in the bottom of valleys while orchards in higher elevations were less affected. In your gardens, this occurs on a small scale with frost pockets that can form in the lowest-lying areas of your yards and garden plots. Antarctica has some of the strongest katabatic winds, with shallow winds that can reach up to 200 mph due to extreme temperature and elevation differences in that continent.

Other local wind names

There are many other location-specific winds and weather patterns linked to wind that occur in other parts of the world. Some are driven by elevation differences, with wind blowing through gaps in mountain ranges (the mistral in France and the tehuantepecer in Mexico, for example). Others blow in specific directions where mountains prevent air movement in some directions, funneling the air into channels that bring characteristic weather to the local area. In northeast Georgia, for example, we have frequent incursions of cold air from the northeast, with air pushed south due to high pressure in northern latitudes that is prevented from spreading to the west by the Southern Appalachian Mountains. We call that phenomenon “the Wedge” due to the shallow and dense wedge of surface air that is pushed by the wind flow into our region numerous times a year. Areas with very persistent topography-driven winds often have trees with most of their limbs on the downwind side of the trunk.

How does wind affect gardens?

Wind causes many effects on gardens. It can blow frigid air into a region from the poles towards the equator, leading to advective frost which causes damage to fruit blossoms in spring. If the humidity of the wind is low, it can quickly remove soil moisture and desiccate plants where irrigation is limited or unavailable. When strong, it can rustle leaves, break limbs, and even topple entire trees, especially where wet ground weakens the anchoring of tree roots. In fact, one measure of wind speed, the Beaufort Scale, uses an empirical scale related to the appearance of waves (on the sea) and tree movement (on land) to categorize wind strength. Some wind is a good thing for many plants because it provides stresses that help strengthen the stems and trunks, but too much can cause a lot of damage from wind-blown debris or direct force on the plants.

What local winds do you see and what impacts do they have on your gardens?

This blog has reached 194 different countries with many thousands of unique visitors a year, so the variety of local winds you experience must be amazing. Some of them are variations on the winds described above, either topography-driven winds like katabatic or anabatic (the opposite of katabatic, with up-valley winds during the day) or foehn winds. Others may develop due to unique geographic features of your area such as the Columbia River Gorge with winds so strong it is a haven for windsurfers. We’d love to see a comment on your local winds and how they affect your gardens!

I close by quoting the famous poem from Christina Rossetti that provided our title for this blog post, one of my favorites:

Who Has Seen the Wind?

Who has seen the wind?
Neither I nor you:
But when the leaves hang trembling,
The wind is passing through.

Who has seen the wind?
Neither you nor I:
But when the trees bow down their heads,
The wind is passing by.

I am constantly slaying horticultural snake oil dragons. There is so much misinformation on the web and even within University/Extension publications. In this blog I turn my attention to compost–a subject that is almost universally cherished by gardeners, gardening groups and horticulturists. Unfortunately there are a lot of misnomers about compost.

Plants are composed of cellulose and cellulose is a complicated polymer of glucose molecules. Compost is made from the decomposition of organic matter—usually plant debris. The composting process can be fast or slow depending on aeration, mixing and pile size. Composting requires a carbon source and enough nitrogen to allow microbial respiration of the sugars contained in the plant material being decomposed. Since the laws of thermodynamics indicate that no chemical reaction is 100% efficient, some of the energy of respiration is lost as heat. Billions of respiring microbes heat the pile creating a very hot environment where thermophilic organisms propagate quickly. As all the available sugars in leaves and other less woody components of the compost decompose the thermophilic organisms lose temperature and the readily available sugars necessary for growth. Other organisms begin to grow and attack the cellulose in the wood fibers, attacking the more recalcitrant carbon in the pile. Eventually most of the sugar bound in plant residues is attacked and only the difficult to decompose materials are left, these contain lignin and form the basis for humus. When the compost will no longer heat after turning it is beginning to mature. Once all the easily broken down carbon is utilized, the microbes die off or form spores and go into a resting phase. The compost is now screened to remove large undecomposed particles and is ready for use in the garden

It’s NOT NATURAL

I have often heard composting touted as a natural process. It is not.
Composting is a process that is “man made”. The alternative is litter fall and mulching which is a natural process that processes organic matter much more slowly. Composting is a process that requires a specific mass of feedstock, sufficient oxygen for respiration, reactions provided by air or by frequently turning the pile, moisture maintained by adding water if needed, and heat which is maintained within the pile itself. These are not natural conditions easily found in nature. They are carefully manipulated by those monitoring the compost process.

The fungi and bacteria on the initial feedstock are part of the ecosystem and are generally not directly manipulated in the process. Fungi and bacteria have the enzyme systems necessary to break the bonds that link the glucose molecules and then utilize the energy in glucose for their own growth.

Composting does not help the environment

As I have discussed, composting liberates carbon dioxide increasing the amount of greenhouse gasses in the atmosphere. On a large scale composting adds many tons of CO2 to the atmosphere as well as oxides of nitrogen which are also potent greenhouse gases. Composting can also release mineral salts into underlying soil and runoff from large composting operations, especially manure composting, can pollute waterways. There is nothing about composting that is helping the environment per se.

Compost is not full of life

Sometimes you hear that compost is “full of life”. Sort of true but not really. The biological processes that break down the compost happen in the pile. As compost matures microbes die, their growth is reduced and they form spores or other resting structures. Once compost is ready for use, it is not particularly biologically active because all the energy has been utilized to make heat and decompose the feedstock. When the energy (carbon, sugar, cellulose) is used up, the microbial activity declines.

What is it good for?

Since compost is a distillation of feedstock minerals it makes an excellent fertilizer. Since compost is mostly fine textured, it is suitable for use in soil as an amendment. The lignin molecules resident in compost help bind nutrients in organic matter and retain them for later uptake by plant roots. Compost can increase the fertility of a sandy soil which has low nutrient binding capacity. Compost is full of secondary metabolites left over from the microbial activity produced when the pile was hot. These compounds can confer disease protection when pathogens are present in soil. Since feedstocks are variable this can not be predicted. Finished composts with a carbon:nitrogen ratio (C:N) of less than 25:1 do not perturb the nitrogen dynamics of most soils and in many cases may be a source of nitrogen in the amended soil. Since compost is mostly broken down feedstock it does not deteriorate as fast when mixed in garden soil. It resides longer than other more labile amendments. Compost is also a great container medium if mixed with coarse materials to assure aeration. Because the compost feedstock is well decomposed, the material has a longer life as a growing medium.

Since composts get hot as the feedstock is broken down, they tend to sanitize the pile of pathogens. Composting kills food-borne pathogens and plant pathogens easily since most do not survive the high temperatures (>140F) found in an active compost pile for more than a day or so. For effective pathogen kill it is important to turn the pile frequently.
Some plants may survive high composting temperatures, e.g, tomatoes are a notorious compost weed. Yellow nutsedge and bermudagrass stolons can also resist the high temperatures found in compost piles.

It’s not a good mulch

One of the amazing things about mulch is undergoes the same processes that make compost and it does have a place in your garden. The microbial processes that decay arborist wood chips on the soil surface happen slowly over months of time. The chips are mineralized but more of the carbon enters the soil rather than the atmosphere because soil fungi, especially mycorrhizal fungi, transform the energetic carbon molecules (labile carbon) into a soil stabile polysaccharide called glomalin. This in turn binds soil particles which increases soil structure. Note: When these processes happen in a compost pile they can not happen again in your garden. The energy is gone.
Texturally fine compost will make greater hydraulic conductivity with the underlying soil and allow for greater moisture loss through evaporation. In some cases compost layers may impede infiltration of water and prevent newly planted root balls from being watered. Compost layers may also impede gas exchange to underlying soils. Depending on the feedstocks, composts may also contain viable weed seeds or other propagules that contaminate landscape soils. Composts make bad mulches.

References

Daugovish, O.,Downer, J., Faber, B. and M. McGiffin. 2006. Weed survival in yardwaste mulch. Weed Technology 21: 59-65.

Downer, A.J.,D. Crohn, B. Faber, O. Daugovish, J.O. Becker, J.A. Menge, and M. J. Mochizuki. 2008. Survival of plant pathogens in static piles of ground green waste. Phytopathology 98: 574-554.

Chalker-Scott, L. and A. J. Downer. 2022. Garden Myth-Busting for Extension Educators:The Science Behind the Use of Arborist Wood Chips as Landscape Mulches. Journal of the NACAA 15(2). https://www.nacaa.com/file.ashx?id=6c7d4542-7481-4f0a-9508-d8263a437348

This time of year, I often get asked for a forecast for the coming growing season. Will we have a drought? Will it be warmer or colder than normal? Will we have any tropical storms in our area? All of these things affect how farm crops (and gardens) will perform over the next few months and how big the yield might be when it comes time to harvest. In this week’s blog, I will look at some of the factors that go into seasonal forecasting and how it all comes down to numbers.

How are seasonal forecasts made?

Seasonal forecasts use computer models to look for large-scale patterns in weather that affect what the climate is likely to be on monthly to seasonal time scales, but also use statistical methods based on observations from previous years to determine what the most likely climate conditions are. The predictions are usually based on several factors, including current conditions, long-term trends, and other regional variations like El Niño Southern Oscillation (ENSO), which we’ve discussed before.

Current conditions are important because they define the starting point of the prediction. If you are starting from a drought, for example, you would not expect that next month would be much wetter than normal because the dry conditions would make it hard for rain clouds to form unless you have an unusual event like a tropical storm or atmospheric river that comes along and changes conditions on the ground quickly. Long-term trends are important because they define the base state of how the climate is behaving. If you are on an upward trend towards warmer temperatures, as we are now with global warming, it is more likely that you will observe a month or season that is above normal than below normal. If there were no trend in temperature, then seasons that were colder or warmer than average would be equally likely. You can find climate trends for your local area using the Climate at a Glance tool and picking your own country, state or county.

Knowledge about regional variations like ENSO also contributes to seasonal forecasts because the atmospheric and oceanic climate conditions which help define those oscillations can last for months or sometimes even years, making long-term prediction easier. The pattern of the atmospheric waves associated with those oscillations defines where warm and cold air are located as well as the position of the jet streams that blow storm systems around. In some respects it is like putting a rock into a river—when you have warm water in the Eastern Pacific Ocean as we do now in advance of the coming El Niño, thunderstorms develop vertically over that warm water, and those towers of rising air divert the flow of air currents that push weather systems around just as a rock diverts the flow of water in a stream. If the warm water were not there, the atmosphere would likely have a very different pattern.

Oirase Mountain Stream – Towada, Aomori, Japan, Daderot, Commons Wikimedia

Forecasts based on ENSO work best when it is at one extreme or the other and in areas where the differences between El Niño and La Niña conditions are most pronounced. That makes ENSO more useful for making seasonal forecasts in the Southeast United States and in northern states where statistical relationships are well-defined than in the central U.S., where there is a weaker statistical relationship between the ENSO phase and the local climate. Climatologists look at similarities between different El Niño years using statistics to identify recurring patterns that can help to predict the climate the next time an El Niño occurs, although other factors can come into play that throw off the forecasts.

How do seasonal forecast maps depict the future climate?

For the United States, seasonal forecasts are presented as maps with probabilities of above, near, or below normal temperature or precipitation. If there was no hint in any of the predictors of what would happen, each of the three categories would have equal weight, or a 33% chance of that climate category occurring. Those forecasts are based on current conditions, what they expect to happen in the months after the prediction made, the long-term trends that are pushing the temperatures or precipitation upward or downward, and the expected state of oscillations like ENSO. You can see the whole suite of 3-month forecasts for the next year for the United States at https://www.cpc.ncep.noaa.gov/products/predictions/90day/.

In the maps above, the outlook for December 2023 through February 2024 is shown. In the temperature map, the climate has a higher probability of being warmer than normal in the northern part of the country, especially the Northeast. This is consistent with the expected pattern of temperature in an El Niño winter. But the prediction of warmer than normal weather in the Southeast is not what we expect if we look only at El Niño. It also includes the effects of greenhouse warming, which is likely to overcome the cooler conditions that would be expected in the Southeast from El Niño alone. On the other hand, since there is not much long-term trend in precipitation, the precipitation outlook on the right shows a clear El Niño signal with wet conditions along the Gulf and South Atlantic coasts and dry conditions in the Northwest and to a lesser extent, in the Upper Great Lakes. In the Southeast, El Niño winters are expected to be cooler than normal because all the clouds associated with the rainy conditions keep daytime temperatures down.

What do we expect for this year?

Because the El Niño is coming on strong, I expect it to drive a lot of this year’s growing season climate. While it is still weak, it won’t have much impact on our regional climate variations, which makes summer difficult to predict. In that case, we look more towards the current conditions and trends to conclude that areas that are already experiencing drought are likely to get worse, and areas that are starting out wet may get a reprieve from drought conditions for a few months.

The biggest impact of an El Niño in the growing season is in how it affects developing Atlantic and Eastern Pacific hurricanes. In El Niño years, tropical systems in the Atlantic tend to be fewer in number and weaker because the strong jet stream aloft keeps tropical cyclone circulation from strengthening into tropical storms or hurricanes. In the Eastern Pacific, it is just the opposite, with more storms forming than usual. That can help feed moisture into the Southwest. Of course, it only takes one storm coming over your home and garden to cause tremendous damage, so you need to prepare for storms if you live in a hurricane-prone part of the United States or other Northern Hemisphere location.

By fall, the El Niño is expected to be well developed and areas where El Niño usually brings rain could see the wet conditions start earlier than usual. For farmers, that means harvest could be difficult if conditions are wetter than usual, and it might be hard to get that last cutting of hay. Winter could be drier than normal in the northern states since many of the rain-bearing storms will be farther south than usual, although you will certainly see some rain.

I just returned from one of my self-imposed retreats where I have no cell phone service nor internet. This means I can focus on writing without interruption. One of my projects this year is to publish a scientific critique of permaculture (stay tuned for that late 2023). Part of my process is to read popular permaculture publications and I am focusing on Gaia’s Garden.  Earlier I’ve posted some general critiques of the book (you can find them here, here, here, and here), but until yesterday I had missed a big, fat problem: a section labeled “The Power of Sheet Mulch” (pages 71-75 in the first edition).

First of all, let me state that part of permaculture philosophy is to follow nature in our gardening practices. There are few examples of sheet mulching in nature. The only one I can think of occurs in deciduous forests, where fallen leaves can create a sheetlike cover several inches deep. Combined with microbial activity and wetter soils, these sheets create low soil oxygen conditions. During the winter the leaves are broken down and by spring have degraded to the point that air and water movement have resumed enough to support plants as they break dormancy.

In contrast, here’s what permaculture recommends. At the outset, let’s acknowledge that none of the practices discussed remotely resembles any natural process. Furthermore, there are no science-based citations to support the practices or the claims of success. It’s completely anecdotal.

A sidebar provides the methods and materials for constructing the “ultimate, bomb-proof sheet mulch.” Here’s a condensed step-by-step breakdown:

1. “Soil amendments, depending on your soil’s needs” are added to the top of the soil before the sheet mulch is applied. How you determine your soil’s needs involves either “us(ing) a soil test or your own understanding of your soil’s fertility to guide the type and quantity of soil amendments.” These include “lime, rock phosphate, bonemeal, rock dust, kelp meal, or blood meal.”
2. A “thin layer of high-nitrogen material” is placed on top of the amendments.
3. Next we “…apply a layer of weed-suppressing newspaper or cardboard (or even cloth or wool carpet).”
4. On top of the sheet mulch another thin layer of high-nitrogen materials is applied.
5. Next we are to add “about 8 to 12 inches of loose straw, hay, leaves…” or any other bulk mulch materials recommended.
6. Then we should add “an inch or two of compost” or “you can substitute manure or several inches of easily compostable material.”
7. Finally “2 inches of…straw, fine bark, wood shavings…” or other listed “weed- and seed-free organic matter” adds the finishing touch.

So. Much. Stuff.

So let’s add this up: a half-inch or more of sheet material, an inch or more of high nitrogen material (from those two additions), 8-12 inches of bulk mulch, another 1-2 inches of compost (or several inches of the substitute), and 2 inches of “the finished look” materials. That’s at least 12 inches of wet (oh, each layer is sprayed down with water as it’s applied), poorly drained material on top of the soil.

I’m all for following nature in how we manage our gardens and landscapes. But deep sheet mulching isn’t natural. It’s bat-sheet crazy.

I think I have a pruning fixation. I take most opportunities that come along to write about pruning. I have not blogged yet about Spring pruning. It can be a useful way to achieve some pruning objectives. Like all practices it is not necessarily the method or timing of method of choice for all plants. Spring Pruning can have some specific impacts on development of deciduous fruit trees that may help in the home orchard.

Springtime may not be the most obvious time to prune–in fact springtime within the geographic context of this blog requires definition. For this discussion, springtime is the period during which buds are opening, shoots are elongating, flowers are pollinated, and fruit is set or is rapidly enlarging. These are changes in the tree phenology that are critical to fruit production. As you may recall from previous blogs on pruning there are some basic impacts that pruning has. Pruning is growth limiting. Pruned parts will grow less than unpruned parts. Spring pruning is an opportunity to regulate fruit retention.

Spring growth and tree phenology are not timed to be the same. Apricots will flower before or after peaches, plums, pears or apples. This can happen in different months depending on latitude of your garden. Spring is in set time back to another vegetative shootand Spring pruning is thus variable across location and species in your garden.

So why is pruning in Spring at all helpful? The main reason is to reduce the number of fruit that are set on a tree. Reducing fruit count will allow more sugar to enter fewer fruit increasing the size of remaining fruit and improving quality.
Pruning during bloom is risky, we don’t know what the fruit set will be until a few weeks later. Also changes in weather such as spring frosts, wind, or even hail and snow can destroy a crop in its juvenile stages and if you have already pruned, you have lessened your changes for fruit later. It’s best to wait until fruit have set, are growing, enlarging and that you are pretty sure the crop is under normal progression.

With a Spring prune I like to remove about half the set fruit. This would involve trimming the ends of branches (that have fruit) by 50 percent. You may still need to thin fruit later because the remaining fruitful stems you leave on the tree may have too many fruit to ensure quality. Thinning peaches to about one every six inches in late Spring, reducing pear and apple clusters to one fruit per spur and minor thinning of plums will suffice. Apricots usually need little thinning for adequate quality.

Another reason to thin in Spring is to reduce disease incidence. Peach leaf curl is usually well developed even as fruit is setting. The best control of peach leaf curl is with a dormant fruit tree spray prior to bud break. But, if you miss that opportunity to spray, pruning out the infected leaves and shoots will decrease the inoculum for next year. Dispose of the infested shoots in the trash (although correct hot-composting will likely kill the inoculum as well).

Spring pruning is not recommended in areas where there are frequent rains, bacterial diseases such as bacterial canker or when your trees are not vigorous and otherwise healthy. Pruning creates wounds that allow pathogens to enter the tree and a wise gardener will avoid pruning during warm showery weather. If conditions are dry and sunny, Spring pruning can be effectively used to slow growth and increase fruit quality for the coming summer harvest.

For more information on the science – and myths – behind pruning, Dr. Chalker-Scott and I published a peer-reviewed article on this recently.