Zucchini Blossom End Rot Treatment: Fixing Blossom End Rot On Zucchini Squash

By Amy Grant

If you have ever container grown tomatoes, as I did this summer, you may be familiar with blossom end rot. While tomatoes are prone to blossom end rot, many types of squash are also susceptible, specifically blossom end rot on zucchini squash. What causes zucchini blossom end rot and is there a zucchini blossom end rot treatment?

What Causes Blossom End Rot on Zucchini Squash?

Blossom end rot on squash manifests itself at the onset as a small bruise on the blossom end of the fruit, gradually softening and darkening in color until it eventually rots.

Blossom end rot is a calcium deficiency that is recognized by the secondary issue of the dark rotting area caused by a fungus. This lack of calcium in the soil is brought about by a number of factors including extreme soil moisture fluxes, over fertilization, or root damage usually caused by cultivation. In the case of root damage, the feeder roots may have been damaged by hoeing.

Plants that bear heavily are also more likely to get blossom end rot since they have a greater need for additional calcium.

Calcium is necessary to the growth process as it engenders healthy cell wall growth. Once the plant has taken up the calcium, it no longer moves from the part of the plant it has been taken to; therefore, it needs a continuous supply of calcium throughout the growing, flowering and producing season.

Preventing Blossom End Rot on Zucchinis

Preventing blossom end rot on zucchinis would be preferable to trying to treat them once they are already afflicted. Test your soil prior to planting to see if it has adequate levels of calcium. The local extension office can help with soil tests.

Also, maintain consistent irrigation and keep the soil evenly moist. Mulch the plants to aid in water retention with organic mulch, like straw, or inorganic mulch, like black plastic. Use care when cultivating around the zucchini as well as tomatoes, peppers and eggplants so you don’t sever the feeder roots which will make the plants think they are under moisture stress and trigger blossom end rot.

Zucchini plants do not need high amounts of nitrogen, which can result in lush, healthy foliage and little to no fruit. Excess nitrogen also causes blossom end rot on zucchini squash, as it blocks the absorption of calcium. Avoid high nitrogen fertilizers and ammonia fertilizers (such as fresh manure) that will stimulate foliage growth, add more salt to the soil and block the absorption of calcium. This is especially true for zucchini, or any cucurbit, grown in containers. They need a fertilizer containing micronutrients, including calcium.

Zucchini Blossom End Rot Treatment

If the plant already shows signs of end rot in the early fruiting phase, you can probably “fix” it by following the above advice along with the addition of calcium in the soil. Calcium is not taken in well by the foliage, so avoid a foliar spray. Calcium needs to go directly to the roots.

Calcium carbonate tablets, or anti-acid tablets like Tums, can be inserted at the base of the plant. They will then dissolve and within a few hours, calcium will be available to the plant.

You can also run calcium through a drip system. Use either calcium chloride or calcium nitrate. This procedure is optimal when the weather is warm and dry. With lovely summer conditions, the plant goes into growing overdrive, using the available calcium at such a rapid rate that the soil is stripped. Feeding through a drip system will give a continuous supply of calcium during the peak growing spurts as well as providing a steady irrigation to avoid water stress which is connected to blossom end rot.

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