Ciscoe Morris, The Seattle Times garden writer, offers tips on thinning raspberry vines, so you get a good crop next year; dealing with "mini-volcanoes" in your yard; and blossom end rot on Roma tomatoes.

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Q. What and when is the right way to thin raspberries? Our patch is huge.

A. Summer-bearing raspberries are easy to prune as long as you understand their growth cycle. Every spring, new canes grow from suckers. These canes will produce fruit the following summer. Once they’ve finished fruiting, they will never produce again. Therefore, remove each cane that fruited by cutting it to the ground as soon as the harvest is over. That will prevent the new canes growing up from getting tangled with the old unproductive ones.

After you remove the old canes, thin the new ones to about every 6 inches, culling out weak canes and allowing only the strongest, most vigorous ones to remain. By the end of the season, the new canes often reach 8 feet or more in height. You can leave them tall, allowing them to bend down over the top support wires, or you can prune the tops off at 6 feet tall to encourage branching and (in theory) higher fruit productivity.

Q. I couldn’t figure out why my mower has been bouncing every which way when I cut the lawn. Then, on close inspection, I found hundreds of little half-inch mini-volcanoes on the soil surface. What in the world is causing this, and how can I make my lawn smooth again?

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A. You’ve got a classic case of too much of a good thing. The little volcanoes are made up of highly nutritious castings (polite way to say worm poop) from night crawlers. Despite the fact that these castings are making your lawn bumpy, it’s good to have plenty of these beneficial creatures around. They aerate and distribute nutrients as they eat their way down through the soil; plus they eat and reduce thatch buildup, improving air, water and fertilizer penetration.

That said, if populations get too high, mowing becomes a jarring experience, and the result is an uneven cut. Fortunately there’s an easy solution: Water the lawn heavily early in the evening, causing lots of the night crawlers to migrate to the surface. Then invite friends over to gather up the worms and take them home to their vegetable and ornamental gardens.

To smooth the bumps, rent a power dethatching rake in mid-September. The machine will not only remove your excess thatch; it also will break up the volcanoes and disperse the nutrients throughout the lawn. Don’t give in to the temptation to push a heavy roller over the lawn to smooth it out. It won’t flatten the bumps, but instead will cause such serious compaction, you’ll beg your friends to bring your worms back.

Q. My Roma tomatoes are finally ripening, but the bottoms of several tomatoes are turning black and rotting. What can I do to stop this disease from rotting my tomatoes?

A. Your tomatoes don’t have a horrible disease; instead, the problem is caused by a physiological condition known as blossom end rot. The trouble starts with a water-soaked spot on the blossom end of the tomato, which soon turns dark and leathery and eventually expands to blacken most of the bottom half of the tomato. The good news is that as horrible as it looks, once you cut off the rotten part, the rest of the tomato is totally safe to eat, and tastes great.

Prevent this from happening next season by working in about 10 pounds of calcium-rich agricultural lime per 100 square feet after harvest this fall. Then, for extra insurance, when you plant your tomatoes, work in a handful of bonemeal under each one.

Finally, try to keep the soil evenly moist around your tomatoes. Tomatoes can absorb calcium only if there is adequate moisture in the soil, and if it gets too dry between waterings, you’ll suffer the same symptoms, even if there is adequate calcium available in the soil.

Ciscoe Morris:; “Gardening with Ciscoe” airs at 10 a.m. Saturdays on KING-TV.

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