There are several reasons that address the question of ‘Why do vegetable plants turn yellow?’. My itty bitty pot of strawberries (leaves) turns yellow all the time. Drives me a little crazy. To be honest, I have yet to eat a strawberry out of that pot because if I am lucky enough for one to actually fruit some animal comes by and eats it before it fully ripens!
But I digress. Your garden plants turning yellow is definitely indicative of a problem. That problem could be one of a few things: nutrient deficiency, pests, overwatering, under watering, not enough sun. That’s basically it. Now, the solutions may not be so easy.
Why are my vegetable leaves turning yellow?
The condition of ‘Chlorosis’ is what causes your leaves to yellow. This is due to a lack of chlorophyll. The three main nutrient deficiencies that cause chlorosis are nitrogen, potassium and iron. There are others but those are the primary culprits.
Too little Nitrogen
You can tell if the issue is a nitrogen deficiency because the chlorosis (yellowing) normally appears at the base of the plant then moves up the stem to the leaves. According to my BF’s at Mother Earth News, this is a major cause for your leaves to turn yellow.
Correcting a nitrogen deficiency
You can organically correct a nitrogen deficiency by giving your plants nitrogen rich supplements such as compost with manure in it or fish emulsion. I am sure you have heard of the practice of putting coffee grounds in your soil to increase nitrogen? There is a legitimate basis for this thought as coffee grounds have about 2 percent nitrogen in them. Tread lightly though as studies have shown adding too much coffee will stunt the growth of plants.
If you’re planting in a garden (versus containers), you can also plant nitrogen-fixing plants which pull nitrogen from the air and pass it to the soil. This is a pretty common and popular gardening method. A couple of suggested edibles are beans, peas and lentils.
Keep in mind too that using these all natural methods may take awhile before you see any solid, positive results.
If you are in need of a quick pick me up, there are organic commercially prepared fertilizers out there such as bat guano. These are not long term fixes though. Your soil needs to be made healthy again. This is where well-balanced compost comes in.
Too little potassium
A potassium deficiency is obvious by the edges of your leaves turning yellow or brown and some may curl-such as carrot leaves.
Correcting a potassium deficiency
Similar to the nitrogen deficiency, potassium can be added to your soil through a mix of fish emulsion and liquid seaweed. Kelp meal is another good element to consider.
A compost that has a high content of food byproducts is also high in potassium (think banana peels). Another organic fix for potassium deficiency is greensand.
It is recommended that you test your soil before trying to specifically adjust your soil’s potassium. Be careful not to overdo things in your enthusiasm to healthify your plants.
Too little iron
Iron deficiencies typically show up as a yellowing in new leaves first (then moves to older leaves). Just like humans, iron is critical to a plant’s development.
Correcting an iron deficiency
Take a wild guess as to what I am going to tell you adds iron back to your soil? No, not fish emulsion. Good guess though! Well rounded compost! Manure (especially chicken), seaweed, garden and kitchen waste all will add iron to the compost thus improving the health of your soil. (Can you see the importance of compost in gardening?)
Check out that Mother Earth News article I mentioned to learn more about the importance of the nutrients in your soil.
Those pesky pests. The types of pests that are the causes of my plant leaf turning yellow are those with piercing-sucking mouthparts such as aphids, spider mites and whiteflies.
I had aphids down in Key Largo and effectively killed them with insecticidal soap. This is a common recommendation. Something else you can do is plant flowers that attract beneficial insects such as ladybugs and hoverflies. They feed on aphids.
Some plants that attract these beneficial insects are sweet alyssum, zinnias, nasturtiums (edible BTW), cosmos and zinnias. In fact, not killing off all the aphids means those new beneficial friends of yours will stick around-because you’re such a good host-giving them all that free food!!
Spider mites are really, really small so it is very hard to detect them. Instead, you see the damage. Insecticidal soap works for killing them too.
Additionally, attracting those beneficial insects is well, beneficial.
Spraying insecticidal soap is also effective in killing whiteflies.
Small warning on using insecticidal soap
Be careful in your enthusiasm to kill those little nuisances. Insecticidal soap can be mildly toxic to your plants. Some tidbits of advice.
· Spray only every four to seven days
· Dilute the spray even more than is recommended on the instructions (assuming you buy commercial insecticidal soap).
· If you have hard tap water, use rainwater or distilled water instead. The chemicals typically found in hard water can actually damage your leaves.
· If possible, buy a commercial soap (versus DIY) as they were specifically created to be sprayed on plants.
· Having said that, I did make my own spray and it did kill the aphids. I believe I may have killed a few spinach leaves in the process but definitely not the whole plant.
I talk about this quite often. I was terrible at watering-until I bought my moisture meter. That whole thing about sticking your finger in to see if the soil felt moist enough just did not work for me.
I am sure this skill comes with many years of practice. My moisture meter has helped me keep my plants alive far longer! Nuff said.
Not enough sun
Yet another cause for the problem of why my plants leaves are turning yellow!
This is a tough one too. Plants (especially vegetables) typically need an average of 6 hours of sun every day. Having said that, some plants like root vegetables can handle some shade. Additionally, you do not want to burn the plants. Not helpful either. If shade is a problem, can you move your plants to containers? Or can you trim your trees and shrubs to eek out as much sunlight as possible?
When we first moved to No Flo, before I planted anything, I spent days walking out to our yard during varying times trying to decide which part of the yard got the most sun (We are surrounded on all sides by pine, oak, piñon, etc. Gorgeous really-just gets in the way of my growing edibles.).
This actually turned out to be quite wise because the one part of our yard which seemed to be the most natural place to put the greenhouse was the worst for sunlight. The greenhouse needs to have a long side facing east without any obstruction. We had to do some serious thinking and maneuvering to make that happen but my plants are doing great in there.
Well, I hope I answered your question of why do vegetable plants turn yellow. It is clearly not an easy answer but thankfully there are fixes and remedies for everything. A small word of warning. Be very methodical about how you solve this problem. You want to research carefully (especially when trying to fix the soil nutrients) before throwing a band aid on the wound. However, with diligence and patience you can get those leaves green again in no time!
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