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Garden Help Desk: What caused these hard cores in my tomatoes?

By USU Extension - | Jan 21, 2023

Courtesy Meredith Seaver

Hard white cores or tough fibrous tissue in tomatoes can result from problems with the balance of nutrients in the soil. Extreme weather problems and also affect the tomato fruits. Good gardening practices can reduce the risk of problems like these.

Most of my tomatoes this year had hard white middles that I could hardly cut through. By the time I finished trimming it away there wasn’t much tomato left. What happened?

Tomatoes with hard white tissue in the center of the fruit have a physiological disorder called internal white tissue (White Core). Garden tomatoes can also develop woody or fibrous cores. It’s common for the affected fruits to look perfectly normal on the outside. There are a few things that can cause the problem.

High temperatures during the ripening period can trigger the symptoms and sometimes it happens because of problems with the soil fertility and the fertilizer program. Some tomato varieties are more prone to the problem than others. Sometimes, insect damage can cause hard or woody cores.

What can you do to improve your chances of a good tomato harvest next year?

You can’t do much about extreme heat next year, but you can do a couple of things to ease the effects. Let the soil warm a bit in the early summer and then mulch the soil around each plant with an inch of compost, a few layers of newspaper, paper grocery bags, etc. This will keep the soil a few degrees cooler. Shade cloth will also help with afternoon heat. Just 20-30% shade will be enough to reduce the temperature of the plant canopies by 2 or 3 degrees, even though it won’t feel shady to you.

Courtesy Meredith Seaver

Late spring frosts can damage the flower buds on plants like the pomegranate.

Get a soil test before next year. Adequate potassium is important for good tomato production. Utah soils are usually high in potassium, but a soil test will tell you whether your garden’s potassium level is too low, too high, or just right. Don’t use potassium fertilizers if your soil is adequate or high in potassium.

High potassium combined with low nitrogen levels can cause white core, as can high doses of nitrogen. Make sure you apply nitrogen in small, regular amounts during the early months of the gardening season instead of infrequent, large applications.

Choose varieties that mention white core resistance or heat tolerance in their descriptions.

Scout frequently for insects like aphids or white flies and protect your plants with insecticidal soap or horticultural oil as needed.

What pomegranate tree grows best in Payson?

Courtesy Meredith Seaver

Pomegranate trees produce lovely blossoms, but our unpredictable weather in the spring and the fall can make successful fruit production difficult.

Most pomegranates need warmer winter conditions for reliable survival and consistent production than you can provide in Payson. There are a few varieties that are described as “hardy,” and claim they will do fine in our hardiness zone. These hardy pomegranate varieties may survive here until we have an unusually cold winter, but you need to consider more than just whether the tree will survive our winters.

Like many other fruit varieties that are somewhat hardy in Utah County, a hardy pomegranate will be more cold tolerant while it’s dormant, but once it begins to break dormancy in the early it will be more susceptible to cold injury. A late-season hard freeze could damage or kill your tree. Or your tree might survive a late spring frost but have all its flower buds or blossoms damaged, leaving you with a “fruitless” tree.

Another common problem we have with trees and shrubs in our area is damage caused by sudden frigid weather following a long, mild autumn. Your pomegranate tree would be more likely to be damaged than other woody plants in your landscape.

Your best options for success are to 1) explore your landscape and identify a sunny, protected microclimate for your tree, 2) grow your pomegranate tree as a potted tree that you can bring into a sunroom or greenhouse during the winter, or 3) move your potted tree into a shed or unheated garage where it will be protected from severe weather once it’s dormant and where it will stay dormant until it’s ready to break dormancy. No matter which you choose, it will be a bit of a gamble.

Some gardeners choose to keep their pomegranate trees pruned in a tree form, but pomegranates are naturally shrub-like in their growth habit. Keeping your pomegranate as a shrub instead of a tree may make it easier to protect during the winter or to move in and out of protected areas as a potted plant.

Here are three pomegranate varieties that may survive here with the right care and planning. Keep in mind that descriptions in plant catalogs and on gardening sites can be optimistic.

Kazake: A bit hardier and more compact, so it’s easier to manage in containers.

Red Silk: Not especially cold-hardy but it has a compact growth habit, making it suitable for container growing.

Salavatski (AKA Russian Red): It’s more cold-hardy than some of the popular varieties.


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