Keep garden fertility in balance

Here in the middle of the growing season, most plants have been chugging along long enough to show wear and tear and the ravages of their advanced ages.

Bug holes are worn like badges of honor in the fight against invading pests. Leaf spots show evidence of continued battles with persistent fungi and bacteria.

At this point in the season, lots of calls start coming to my desk about plant problems that many think are diseases but actually are signs of nutrient deficiency or even nutrient overabundance.

Unfortunately, these disorders take a while to correct, resulting in plant damage and reduced harvest before the problem can be fully addressed. Catching the signs early will definitely help get plants back to a picture of health in no time.

Nitrogen balance

Many times over the course of the summer, frantic gardeners call me about what they think is a blight affecting their plants. Most commonly, it is about tomatoes or beans, but this problem can affect any garden plant, especially those that produce fruit.

The symptoms they describe are the yellowing and eventual death of the bottom leaves of the plant, but no other signs of trauma, such as leaf spots, blotches or holes.

Instead of suffering from a disease, these plants suffer from a lack of nitrogen. If there are spots or blotches, a disease is most likely the culprit.

The nutrient nitrogen is what we call a “mobile” plant nutrient. This means that when the plant has a lack of nitrogen, it takes it away from the older, bottom leaves to feed the new growth at the top of the plant. In effect, it is sacrificing the old to feed the young.

A little bit of this does not cause a problem, but over the long term it can affect the production of the plant.

To these gardeners I suggest an application of fertility that will boost the nitrogen level in the soil. You can use common fertilizers like basic 10-10-10 (that first number is the percentage of nitrogen) or even a small amount of straight nitrogen fertilizer like urea (46-0-0).

Composted manures do have nitrogen, with poultry manures having the highest level (the white part of bird manures is basically their urine, which is rich in urea).

But here is where we must keep a delicate balancing act. If we apply too much nitrogen too early to the plant, it greatly reduces the flowering and fruiting of the plant.

Nitrogen supports the growth of leaves and stems in plants. So much so that in excess, nitrogen can cause plants to bloom poorly or not at all, resulting in very little production.

This is why I suggest fertilizing with a moderate nitrogen fertilizer when planting and until after blooming and fruiting is well underway, then side dressing with the higher nitrogen fertilizers to keep the plants from declining.

Calcium conundrum

You wait patiently as your first tomatoes start to ripen, hoping for that first tart, juicy fruit of the year, only to find that the bottom part of the tomato has rotted.

This is another major issue I hear about from woeful gardeners this time of year. Those who aren’t in the know blame a blight or some other disease. Of course, they couldn’t be further from the truth. The problem here is a lack of calcium.

Fruits have lots of different compounds at work inside, from the sugars that make them sweet to the cellulose that gives them structure (and us fiber).

Calcium is an important element in the formation of plant cell walls, acting as sort of a “cement” to hold things together.

The blossom end of a tomato (or other fruit — it can happen to more than just tomatoes) is a rapidly growing area and therefore has lots of newly developing cells.

Unlike nitrogen, calcium is not mobile in the plant. Once the plant has exhausted its store of calcium, the new cell walls become weak and cannot support themselves. The walls collapse, resulting in necrosis (death) of the end of the fruit.

Unfortunately, this is an irreversible condition. Any affected fruit cannot be saved, and increasing the calcium needed to avoid further problems can take time.

This problem can be caused by a lack of calcium in the soil. Aside from raising the pH of the soil, adding lime adds calcium to the soil.

Lime is very slow acting in the soil, so once you see the signs of blossom end rot, adding lime will not help this year.

There are products available with an absorbable, quick-acting calcium such as calcium nitrate or calcium chloride that you can spray on the plant to correct the deficiency. But there are also other potential issues that can cause blossom end rot even if there is enough calcium in the soil.

One major problem we commonly experience is uneven watering.

Calcium is taken up into the plant through water entering the roots. If there is a lack of water, then new calcium isn’t taken into the plant. But overwatering can be an issue as well.

When we have periods of long-term rains (like we did in June or most of last summer), or if you overwater your plants, the very delicate root hairs that grow all along the roots can be killed off. These hairs are needed to help the plant take up the calcium, so losing them can result in blossom end rot.

Another problem that can cause or worsen blossom end rot is overfertilization.

If you make your plants grow too fast, the rapid growth makes it hard for the plant to take up enough calcium to keep everything happy. This problem typically arises from too much nitrogen or phosphorous. So here again, it is important to find balance in fertility and in water for the plant.

Getting a leg up

So here’s where I get to stand on an extension agent’s favorite soapbox and lecture about the importance of soil testing.

It is always our recommendation to test your soil in the fall and apply the lime you need before winter sets in so that it has time to break down in the soil. Soil testing will also tell you how much nitrogen, phosphorous and potassium you need for optimal plant health.

To have your soil tested for free, visit or contact your county extension office to find directions and download the form to accompany your sample when you send it to the lab. It might just help you avoid these issues altogether.

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