Sign up for Greenhouse Gases -
a weekly-ish newsletter that will teach you the science behind regenerative gardening, with action steps to help you make a difference in your backyard.
Have you ever wandered through your garden, only to stop in your tracks when you notice something... off about your plants?
Maybe you noticed yellowing leaves - or even weirder, a purple tinge. It might be the oddly shaped carrots or radishes you only notice at harvest time, or the squashes blooming before its time.
I'm here to tell you -- these aren't just quirks of your plants. They're messages. Kind of like little postcards from the underground world of your garden. Each plant issue is signal about what’s happening beneath the surface.
Learn to interpret the signs, so you can understand the nutrients your crops are craving. Eventually, you'll become fluent in a language that your garden speaks. It helps you turn any nutrient problems into an opportunity to nurture your soil back to health.
So, before you rush to pour some fertilizer on the soil with abandon, let's take a moment to decode these leafy messages. By understanding what your plants are saying, we can give them exactly what they need. You'll be able to grow healthier food and build a more balanced garden ecosystem.
Check out the decision chart below. You can match your plant's symptoms with their potential corresponding nutrient shortage.
I recommend that you keep reading to learn more about the nutrient deficiency. In certain instances there's a fine line between deficiency and toxicity.
Over-fertilization can lead to ecosystem damage and pollute surrounding waterways. You can harm soil in a way that is difficult to fix. Remember: we're here to be sustainable!
Have a look at the interactive table below. You'll see a list that clarifies the distinction between each "postcard message" on plant foliage.
Observe the feedback your crops are telling you. They’re like soil interpreters themselves. But you have to be able to understand their language to understand the translation.
Plant health reflects your garden's conditions and microbial activity.
It’s best to look at this from a holistic approach rather than in isolation of a specific nutrient. How can you make a change in the soil ecosystem in addition to fertilizer?
Deficiency Symptoms:
• Older leaves yellowing
• Yellowing moves from tip of the leaf down to the base
• Overall growth can be stunted
Are your older leaves turning yellow from top to bottom? This is a way that vegetation communicates with you about their nitrogen levels (hawaii.edu).
Nitrogen can move around in plants. This means you'll usually see indicators of low N (yellowing) on older foliage. As an adaptive strategy, the plant gives any of the precious nitrogen for the younger leaves (iastate.edu).
I saw this happening this year with my garlic crop. It was planted in an area that could have benefited from a good dose of our goat manure. I decided to supplement with blood meal and compost. These aren't instant fixes, so it took a few weeks for me to notice a shift in overall health.
Here's an important consideration when looking at organic vs. synthetic inputs: Crops can't absorb around 50-70% of applied synthetic nitrogen fertilizers (Yamaguchi)!
This is bad for three reasons:
Be mindful of the environment, and avoid over-fertilization. It's always best to apply organic amendments to your garden (more on that later).
Wool pellets are a great source of slow-release nitrogen, especially for heavy feeders that are prone to getting eaten by slugs. Slugs aren't big fans of the texture of wool. I like to form a mulch circle of these pellets around brassicas for this reason. Aged chicken manure, worm castings, or nitrogen-fixing cover crops like hairy vetch or fava beans are other ways to add accessible nitrogen to your garden. Nettle compost tea is another easy-to-source fix to try (moulton college).
Nerd out with further reading from USDA & Frontiers in Plant Science
Deficiency Symptoms:
• Older leaves turn reddish-purple-blue
• Plant tissue can also be an unusually dark shade of green
• Root growth and overall plant growth can be stunted (hawaii.edu)
Have you ever seen a plant leaf turning shades or red, purple, and blue? It can be both beautiful and surprising. You might see this more often in colder weather. Did you know that low temps can actually limit phosphorus availability in the soil (iastate.edu)?
The reason for the color change? It's due to anthocyanin accumulation in the leaves (PSU). Anthocyanin is the pigment responsible for the deep reds, purples, and blues that you see, and offers protection to the plant (Journal of Biomed Biotechnol). It's a stress response -- this helps the leaves balance light stress while maintaining photosynthesis (Plant Stress).
It's important to mention that some plants have foliage that is actually meant to be blue or purple! Some examples include purple varieties of Asian greens or blue cultivars of leeks. I recommend that you make sure the leaves aren't supposed to be these hues before you add phosphorus.
Natural inputs like fish bone meal, manure, and vemicompost are great sources of phosphorus. Cover crops like grasses and radishes help with P accessibility (Cover Crop Strategies). No-till practices that encourage mycorrhizal relationships can also help. Mycorrhizae -- beneficial fungal networks in the soil -- help make phosphorus more accessible (UNL).
Want to go deeper? Have a look at PMC10421280
Deficiency Symptoms:
• Older leaves turn yellow, from tips through the edges
• Yellow can also show up as spotting (uconn.edu)
• Stem/stalk will become weak
• Fruit will be small or abnormally shaped (hawaii.edu)
Potassium is a mineral that causes me a bit of a conundrum. As you likely know, it's a major nutrient for crops. Potassium isn't easy to source, especially in natural amendments. Have you noticed that the NPK levels in your organic fertilizers are never that high for the last number?
Organic potassium is available from mining rocks, which usually isn't a sustainable process (UNEP).
Are there other sources? Wood ash has potash in it, but levels are never predictable. Worse still, applications can shift your land into uninviting conditions (aces.edu).
Wool pellets are a decent source of potassium, with a NPK of 9-0-2 (the 2 is the potassium amount). I love to add wool pellets around plants prone to slug damage, since they don't like the texture. Comfrey is a permaculture darling plant that accumulates potassium. You can chop and drop the leaves or make a compost tea fertilizer (Horitculture).
If you live on the coast, you might be able to harvest kelp and other seaweeds for a slight K boost (ucanr.edu). Be sure to look up local regulations before harvesting.
I've seen new products with high levels of potassium sourced from aloe vera. However, I've yet to try them out myself. One example is VivaBoost. Their product is a North American-sourced brand and OMRI listed for organic farms.
Additional info: Biology (Basel), Plants (Basel)
Deficiency Symptoms:
• Older leaves become yellow or orange, but veins remain green (hawaii.edu)
• Base of leaf can also remain green (UFL)
• Older leaves will have dead spots (iastate.edu)
A magnesium deficiency can be like a domino effect. Magnesium helps other nutrients to move around the plant properly (Front. Plant Sci). So once Mg is low, plants may start to show signs of other issues too. Even if those nutrients are present, low Mg levels can render them inaccessible to your crops.
Interestingly, over-fertilizing your crops with potassium and ammonium can deplete magnesium availability. This is especially true if your garden is sandy or acidic (Int J Mol Sci, iastate.edu).
How can you fix low magnesium levels? It can be challenging to find Mg in organic fertilizers. It's included in the blend by Organic Plant Magic, which is one of my favorites to use in my garden. Azomite and dolomite are other sources.
A common household fix for magnesium that I've seen gardeners apply is epsom salts. There are a few downsides to this that you should know:
• It can make your soil's saline levels too high, which can be a detriment to vegetable crops (Clemson).
• Salty soil can negatively effect beneficial microbes (Petrić et al).
• While magnesium helps with nutrient transport, too much of it can actually cause the opposite issue. This limitation is especially true with calcium. So high levels of magnesium can lead to blossom end rot in your tomatoes and peppers (NDSU).
Further Resource: frontiersin
Deficiency Symptoms:
Low calcium is usually what comes to mind when we see blossom end rot in our garden. Plant cells need calcium to form their membranes. So low levels of this mineral can cause tissue in the fruit to not form properly (UWM, UGA).
An important note that I learned a few years ago when I saw BER on my tomatoes: uneven watering can cause inconsistent access to calcium (UWM). At that point, I hadn't installed drip irrigation in that part of the garden yet. Once I got that set up on a regular timer, the issue resolved the following year.
Look for balanced sustainable fertilizers that have calcium added. I like Organic Plant Magic for this purpose. You can also use eggshells too. Be sure to watch this video from Canadian Permaculture Legacy to see how to process them.
Deficiency Symptoms:
As regenerative gardeners, we're likely already helping our crops access sulfur in the soil. Since sulfur can be brought to plants through mycorrhizal relationships, a no-till garden high in organic matter likely won't have a sulfur issue (iastate.edu).
In my research, I learned that sulfur is part of the nitrogen fixation process -- where nitrogen gas from the atmosphere is turned into a form that plants can absorb as a nutrient. This is important to know for legume crops (Frontiers Plant Science).
How do you solve low sulfur? Look for full-spectrum fertilizers with soil microbes (Frontiers Plant Science). For example, Organic Plant Magic has both sulfur and beneficial microbes that help deliver it to root systems. Debris from brassica cover crops can provide this element for the next season, too (Schwab).
Gypsum is often recommended for a lack of sulfur, but there are a lot of caveats to this input. Gypsum is only really beneficial for compacted heavy clay that also is saline and sodic (Down to Earth).
Learn More: nih.gov
Could your efforts to boost plan growth inadvertently harm your backyard ecosystem? The balance of micronutrients is more delicate than you might think.
I've intentionally not included a lot of information about micronutrients in this article. This isn't because I don't want the article to be comprehensive. It's because I don't want to recommend that you target these nutrients without a soil test.
My caution is due to micronutrients being easy to "over-fix" to the point of toxicity. This can spell disaster for your garden's health, your crop yields, and the environment too.
If you suspect a micronutrient deficiency, it's important to confirm with a soil test. I'd also try to solve the issue with a local source of herbicide-free manure. Well-ages compost and manure contains a wide range of elements. This can support your land without overloading it, and nurture a balanced ecosystem.
Deficiency Symptoms:
Chlorosis is the botanical term for yellowing of leaves.
Iron insufficiency is more common in soils that have a high pH (alkaline) and are high in calcium (iastate.edu). Need an easy ways to boost iron levels without risking toxicity? Add compost, herbicide-free poultry or rabbit manure, or seaweed. Blood meal can also support iron levels while boosting nitrogen, too (Farmonaut).
Dive Deeper: mdpi
Deficiency Symptoms:
Another point to consider when diagnosing your plants is that this mineral is usually only low in sandy spots or in the tropics. A word of warning: If your soil is acidic, it's at a higher risk for manganese toxicity (wisc.edu). In general, applying a straight manganese amendment isn't recommended.
Further Reading: nih.gov
Deficiency Symptoms:
Sources: nih.gov, hawaii.edu, UFL
Deficiency Symptoms:
Do not amend with copper without running a comprehensive soil test first. This shortfall is usually seen in sandy areas.
Sources: umn.edu, UFL, hawaii.edu
Deficiency Symptoms:
Sources: msu.edu, iastate.edu, nih.gov, hawaii.edu
My plants clued me into a boron deficiency when I saw my radishes and beets grew hollow, and brassica stems were hollow, too. This issue presented itself in the first year gardening in previously uncultivated spot. Adding aged manure, growing cover crops, and mulching did the trick to fix the issue.
Highly recommend testing soil before supplementing with boron to avoid toxicity.
Deficiency Symptoms:
Usually molybdenum only occurs in soil that is very acidic (iastate.edu) or sandy. In legumes, you might see this paired with a nitrogen problem. Molybdenum is needed for bacteria and plants to work together and fix nitrogen (hawaii.edu).
Chlorosis is the botanical term for yellowing leaves. It's a symptom that needs to close examination to accurately diagnose nutrient issues.
University of Hawaii points out the following distinctions. Yellowing on...
The plant forming in a funky way could be either a boron or calcium problem. According to the University of Hawaii:
A boron deficiency is usually seen in root vegetables. Signs include elongated roots that are thin, and in general misshapen. Radishes, beets, and carrots can even have a hollow center. You might also see this in brassica stems -- they can be hollow, too.
A lack of calcium shows up as curled or concave young greenery. Blossom end rot can also cause dark spots on the bottoms of your tomatoes, peppers, and squash.
When fixing nutrient levels, it’s important to make sure you're using an organic product.
Organic fertilizer feeds the microbes that build relationships with plants. Soil microbes can deliver nutrients to your crops. We want to foster this relationship!
On the other hand, synthetic fertilizer skips over this process. Microbes don't need to deliver these nutrients. Over time, crops stop forming beneficial relationships with microbes. This is not something a regenerative gardener wants. Soil life builds soil health to give us a more resilient garden (teaming with microbes).
Natural fertilizer needs the microbiome to make the nutrients available to plants (OSU).
There are other reasons why we want to only apply organic fertilizers to our crops. Synthetic fertilizers have a high carbon footprint because they are typically made from petrochemicals (POPSCI).
Did you know that synthetic nitrogen fertilizers account for 2% of global emissions (phys.org)? Put into perspective, that’s the same amount released from commercial aircraft globally!
The use of synthetic fertilizers, particularly nitrogen-based ones, significantly impacts the environment. When applied excessively, nitrogen can leach into waterways, leading to pollution and contributing to algal blooms that deplete oxygen in water bodies, harming aquatic life. Excess nitrogen in the soil can volatilize into the atmosphere, forming nitrous oxide—a greenhouse gas approximately 300 times more potent than carbon dioxide in trapping heat in the atmosphere (phys.org).
To mitigate these effects, prioritize using organic fertilizers that release nutrients slowly, reducing the risk of runoff and volatilization. Growing cover crops and practicing no-till farming can also help retain soil structure and fertility. It's possible to promote natural nutrient cycling without the need for synthetic inputs!
A fascinating fact I learned while researching this article: nutrients fuel photosynthesis.
Quick refresher: photosynthesis is how plants use sunlight to synthesize food from carbon dioxide and water, releasing oxygen.
The healthier a plant is, the better it will be at processing sunlight into a food source for itself.
But here's a connection that few gardeners think about. We can support plants with nutrients to optimize photosynthesis... which in turn improves carbon sequestration in the soil. Carbon sequestration is a process of capturing and storing atmospheric carbon dioxide -- a greenhouse gas that contributes to climate change -- in the soil.
Why? Well, during photosynthesis plants work together with their microbe friends to bring atmospheric carbon down into the soil. This is one of the most promising nature-based solutions to climate change.
Look at it a little more closely:
Since you read about the role of sustainable inputs earlier, you know conventional fertilizer isn't a climate change solution.
Instead, it's a slow and intentional process of building up a balanced ecosystem. It's not just organic fertiizers alone. It's also other no-till practices, like mulching, compost, manure, and cover crops.
It's not a one-and-done solution. It's a continual tending to the land.
In this series, we've explored the leafy messages of your garden, from nutrient signals to soil health indicators. Each symptom and solution brings us closer to understanding how to nurture a resilient and flourishing garden. Ready to decode more messages? Dive into the next installment to keep your garden thriving.
