We hear the word carbon thrown around a lot: carbon copy, carbon footprint, carbon life forms.
 
But what is carbon, and what does it have to do with gardening?
 
Carbon is an element found in all living things. In fact, carbon is second only to oxygen in our bodies.
 
Carbon can take many forms. It can be the graphite in your pencil, the diamond on a wedding ring, a gas, or a liquid. It is also found in the compost, manure, and plants in your garden. That adaptability, paired with its ability to bond easily with other atoms and molecules, is probably why we find it almost everywhere, including in our garden.
 
How plants use carbon
 
Carbon is fundamental to life as we know it. Plants pull carbon dioxide from the air to use in photosynthesis in a process called the Calvin cycle. Carbon is also used to make cellulose.
 
Cellulose is what gives plant cell walls their structure. Combined with lignin, pectin, and a few other materials, carbon is what holds trees and plant stems upright.
 
Did you know that the cotton fibers in your T-shirt are one of the purest forms of cellulose? I didn’t either.
 
Carbon in the soil
 
Soil carbon is a term used to describe the amount of solid carbon found in soil. That carbon comes from inorganic carbonate minerals. It also comes from all the carbon-based life forms living in and on the soil, like beetles, microorganisms, and worms. When those creatures poop or die, their carbon becomes part of the soil organic matter that plant roots call home. The same is true of neighboring plants. As they decompose, their carbon is stored in the soil. Carbon improves soil structure and keeps plants healthy and productive.
 
It’s been that way for millions of years. Until recently.
 
Commercial farming and deforestation have created problems regarding soil carbon. The use of heavy machinery and excess digging kicks carbon into the atmosphere as carbon dioxide, contributing to climate change and reducing soil carbon levels. Reduced carbon levels also impact the effectiveness of nitrogen fertilizers. Or maybe it’s the other way around.
 
Research conducted at the University of Illinois at Urbana-Champaign discovered that farmed soils have shown a significant reduction in soil carbon levels since farmers started applying synthetic nitrogen fertilizers in the mid-1950s. The more nitrogen that was added, the more carbon was lost from the soil.
 
Fertilizers cost money. We don’t yet know if adding the fertilizer makes plants grow more quickly than the soil carbon can be replaced, or if it is something else. Too much nitrogen creates nitrogen pollution, as well. For me, this stresses the importance of lab-based soil tests. Our plants need nitrogen, but too much of a good thing can easily become a bad thing.
 
And lost soil organic matter translates into lost water. Healthy soil needs carbon, microorganisms, and time to process and store water effectively.
 
Putting carbon back into the soil is not a simple matter of burying some charcoal or using biochar. These things are delicate chemical interactions.
 
How to retain soil carbon
 
We can help our garden soil retain the carbon our plants need and reduce the amount of carbon lost to the atmosphere with the following tips:

• Add fruit- and nut-producing trees, shrubs, and perennials to your landscape.
• Avoid digging and rototilling when unnecessary.
• Consider transforming your lawn into a meadow or letting the grass grow taller.
• Improve biodiversity in our gardens and garden soil.
• Install more native plants.
• Protect soil against erosion with cover crops and green manures.
• Use compost and aged manure to fertilize your plants and return some carbon to the soil.
• Use fewer or no chemical pesticides and herbicides. They negatively impact biodiversity, and their production generates greenhouse gases.
• Use lab-based soil test results to only add necessary fertilizer.

 
We can improve soil health and soil carbon levels with just a little effort. I think it’s worth it.

Leaf drop is a type of abscission. It can be a normal part of a plant’s life, or it can be a clue to a problem.
 
As plants age, they often lose older leaves. That’s normal.
 
As days shorten and temperatures drop, deciduous plants break down the chlorophyll in their leaves before dropping them. That’s normal, too.
 
But sometimes leaf drop is a plant’s way of telling us something is wrong. Below is a list of the most common causes of abnormal leaf drop:

• Collision damage—high-traffic areas can be hard on plants
• Improper humidity or watering—too much or too little
• Inadequate or sudden changes in light levels (light shock)
• Nutrient deficiencies--iron, magnesium, nitrogen, phosphorus, potassium, zinc
• Pest infestations--mealybugs, scale insects, spider mites
• Temperature—drafts, sudden changes, too cold or too hot
• Transplant shock--dividing, repotting, relocating

 
The best way to keep your plants healthy is to start with species suited to your microclimate and USDA Plant Hardiness Zone. Then, place them where they will get the sun exposure (and any wind or traffic protection) they need.
 
Monitor your plants regularly for signs of pests or disease. It’s a lot easier to nip problems in the proverbial bud if they are caught early. And get your soil tested every few years. It’s the only way to see what your plants have on their menu.
 
The Number One cause of abnormal leaf drop is water.
 
Too much water can drown your plants. It can also make them more susceptible to pests and diseases, and generally make them miserable. Leaf drop is a symptom of too much (or too little) water.
 
Give your plants the water they need, and no more.
 
An inexpensive moisture meter can help you prevent overwatering. The easiest rule of thumb for most containerized plants is to wait until the soil starts pulling away from the edges of the pot before watering.
 
If leaves are falling off your plant at the wrong time of year, use these clues to help you find out why. Once you know the cause, you can find a solution to your plant’s problem.

Chipmunks, deer, groundhogs, livestock, mice, rabbits, rats, squirrels, and occasionally voles will also cause leaf damage.
 
Nutrient disorders that cause leaf damage
 
Healthy leaves are deep green, to one degree or another. It depends on the plant species.
When things start going wrong, they may turn into paler versions of themselves. This yellowing, or chlorosis, can be due to nitrogen or potassium deficiencies.
 
Other symptoms (and causes) of nutrient-based leaf damage include the following:

• Burnt or dead leaf edges may mean there is too much salt in the soil for that plant.
• Purple-ish older leaves may indicate a phosphorus deficiency (or low soil temperatures).
• Yellowing alongside green veins (interveinal chlorosis) may indicate an iron or magnesium deficiency. It may also mean poor drainage or high soil pH.
• Yellow leaf edges, combined with weak stems, indicate your plants may need more potassium.