Reading leaves
This time of year, after the new plants have been in for a bit and the old deciduous ones have put out their new leaves, it's a good practice to be paying attention to how your plants are getting along. Leaves are the primary way a plant has to tell us what is going on with it. When they're lacking in water, they wilt. When insects or disease attack, it almost always shows up on the leaves. Same is true for the plants' nutrition. When the plant is lacking and sometimes overfed certain nutrients, the leaves will be the first indicator. So, here's a few tips on the nutrients and what to look for.
The macro nutrients. We humans have come to the conclusion that there are 3 nutrients that a plant needs the most of. (that's another post for when I'm feeling confrontational)! NPK is how they are listed on packaging and just like any product, the ratio of each nutrient is listed as the "ingredients" on the back of the packaging. It's the law! It's a good idea to get used to reading them when you're wanting to purchase a fertilizer, because some brands, well known brands, are heavy handed at nitrogen when there is no need for them to be.
So lets start with nitrogen.....think green growth. Lush grass that grows fast, when it is applied to a lawn. Nitrogen is essential for plant growth and a healthy dark green color to the leaves. It is also the most common deficiency in a plant. Nitrogen leaches out of the soil quicker than any other nutrient. You can tell, by the leaves, if a plant is needing N. All the leaves, top and bottom, will show a N deficiency. Many things can cause a leaf to turn yellow, but if a leaf is yellow with reddish veins, than it's nitrogen deficiency. A plant will come out of it quickly once you add nitrogen, but please be careful and don't overdo it. More is not better. You can kill a plant with too much N and it also makes the plant grow too fast and weak. Research has also shown that plants artificially fed high doses of N are more susceptible to disease and insects problems. Blood meal, fish emulsion, manure (aged first) and of course, compost are good sources of N.
The oldest leaves on a plant are the first to show these nutrient deficiency and the oldest leaves are at the bottom of the plant or next to the trunk. These nutrients travel to the shoots and new leaves at the top of the plant first and then make their way down the plant. (The plant is thinking of survival first and foremost and the "babies" get the food first).......
Phosphorus (P) - P is essential for cell division which has to happen for growth. It also helps a plant fight disease and for strong roots. What I remember it most for is it's essential for flowering which leads to seed production. If you notice on the packaging for fertilizers that help a plant flower, bloomboosters etc..., the middle number which is phosphorus, will be high. Deficiency starts on the old leaves as mottled yellow between the veins, but what I always notice first is the plant is stunted and the leaves have a purplish cast to them on the undersides of the leaves and the stems. The older leaves will eventually fill will brown spots, turn all the way brown and fall off. The newer shoots and leaves are also a duller green. I have seen with bagged soils that if there is any kind of nutrient deficiency, it will be in phosphorus. Bone meal, ground rock phosphate and compost are good sources of P.
Potassium (K) - K is vital to photosynthesis, helps a plant fight diseases, cold weather and drought. I always think of this nutrient as helping keep a plant strong and in good fighting condition. Watch the leaves and if the margins start to turn reddish, become scorched looking or grey, grow brittle and then fall off leaving just the center of the leaf hanging, you have a K deficiency. There can also be yellow streaks or spots on the leaves along with the scorching look. Greensand, granite dust, manure and compost are good sources. So are plant residues, so it's a good excuse to not be so tidy! Hey, I'm just helping the potassium!
Zinc and magnesium are micro-nutrients. The plants don't need such a large amount, but all nutrients are essential. Even a teeny-tiny amount of a nutrient that is not present can affect a plant. These two also show up in the older leaves. When zinc is in short supply the leaves will be misshapen and have a funny color to them. The leaves will usually fall by mid-summer. Magnesium deficiency can be told by the leaf being blotched either grey/brown or yellow with the vein remaining green and these leaves will fall off by mid summer too. Deficiencies are not as common with these two. Compost will solve it but if you need a quick fix, read the labels for the list of micro-nutrients.
There are many more micro-nutrients that a plant needs. Most are found abundantly in the soil as long as you add compost and don't over chemical fertilize your soil. This whole post is really the strongest argument for compost. Think of compost for a plant as we do food. We eat a balanced meal and through food get the nutrients we need as our body needs them. Slow and steady. Same with a plant and how it uses compost. It will take up from the soil what and when it needs certain things. Now think of the chemical fertilizers as we might a vitamin. Sure, we can get minerals and vitamins through a pill, but that can not sustain our bodies. Same as with chemical fertilizer and plants. You can get by with them for a season with an annual or as a quick fix, but in the long run, salts from the chemicals will build up and kill the plants. The bacteria and worms in the soil can not live on chemicals, not to mention the soil structure needs constant regeneration that it only gets through decomposition or through compost.
I hope this rambling hasn't been too boring, but before we figure a problem with a plant is a disease, as we all have done, stop and watch the leaves first. The plant just might be hungry! Our plants have a way of communicating with us when we stop and listen!
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