You started your tomato seeds in March, planted them in the ground in May, and you’ve been taking good care of them since. You water, fertilize, and weed with care, or so you think. And finally, all your hard work is beginning to pay off. Your beautiful plants are producing colorful and beautiful tomatoes, and visions of tasty salads and tangy salsas are dancing in your head.
And then, it happens. You go to pick some of those beautiful fruits and you discover, to your horror, that several of them have hard, ugly, sunken, misshapen, gnarled black spots on their bottom halves, and your tomato dreams dissolve into nightmares. “What happened,” you cry.”Where did I go wrong!?”
What happened is a condition known as blossom end rot. Blossom end rot is caused by a deficiency of calcium within the plant tissues. This often happens when plants grow rapidly during a wet spring and then fruit set occurs when the weather turns dry. The plants are rapidly absorbing calcium which suddenly runs out. The fruit damage occurs when the fruits are first beginning to mature, and by the time the fruits become full size, the water-soaked, black, leathery spots become evident.
Several factors can cause this calcium deficiency. Fluctuating soil moisture levels, too much nitrogen in the soil (often caused by over-fertilization), root damage due to overzealous cultivation, cold soil, soil with too high a pH, and soils with excess salts.
So how can you prevent this awful condition? In several ways.
1. Make sure you are providing the soil with a consistent level of moisture. If rain has been in short supply, make sure that you water your tomatoes deeply (to a depth of about six inches) at least once or twice per week.
2. Mulch around your tomatoes to prevent moisture loss. As a side benefit, mulch will also suppress the growth of many weed species, which will reduce the amount of time and effort you have to spend weeding.
3. Spray the plants with a calcium supplement such as Tomato Rot-Stop by Bonide® or Enz-Rot™ Blossom End Rot Concentrate Spray.
4. Make sure the soil has warmed up in the spring before you put your tomatoes in the ground.
5. Go easy on the fertilizer, especially high nitrogen fertilizers such as manure. Use fertilizers that are lower in nitrogen, but higher in phosphorous.
6. Keep records of your garden. You may discover that certain tomato cultivars tend to be more susceptible than others to blossom end rot. Armed with this information, you’ll be able to plant the least susceptible varieties.
Follow the above advice, and you will be able to say, in the words of Lady Macbeth, “Out, out damned spot!”