Dear Miss Floribunda,


I shared your June column about the quickest/easiest ways to have a vegetable garden with my son and his housemates. The idea was that they’d stop raiding my tomato patch and grow their own stuff. Because they are less-than-athletic “mouse potatoes,” I expected them to go out and buy pots of tomatoes. Instead, they told me they were looking to the future and were going to prepare an in-ground bed they could use every summer. Well, my digerati are way too high-tech to dig with spades, so they went out and bought a battery-operated posthole digger. It actually worked well, and the tomato plants they put in are looking good, full of flowers. 


I do have a quibble, though. While they don’t keep a compost pile because they generally eat out or just nuke a pizza or something from a package, they do keep their Nespresso Prodigio coffee machine in almost constant operation, sometimes by using their smartphones when they’re out so they can have coffee as soon as they get home. These caffeine fiends throw mega amounts of coffee grounds directly on their tomato plants every day. I’ve tried to tell them this isn’t a good idea for their plants, not to mention what the caffeine and acid is doing to them personally. They must have read your last column about soil pH and hydrangeas in the online Streetcar Suburb News, because they sent me the following text: “Ms. Flo says worm dirt OK on mopheads Y not tomatoes?” OK. “Y” or “Y” not?


Grounds for Concern on Gallatin Stree


Dear Grounds, 

DSC 8489
Overly acidic soil can result in tomatoes with blossom-end rot.
Courtesy of Corey Twyman

Actually, your digerati are correct to call coffee “worm dirt.” It makes good mulch, and worms do like those spent grounds. Once used, coffee grounds lose most of their acidity but are still full of such beneficial elements as copper, magnesium, potassium and phosphorus. They also judiciously release nitrogen and promote the development of important microorganisms in the soil. And while coffee grounds do attract worms, they repel slugs, snails and ants, and I’ve even heard wild claims that in quantity they keep squirrels away. It’s true that over time too many such grounds would lower the soil pH (“potential hydrogen,” or hydrogen ion concentration, and a measurement of the acidity or alkalinity of soil) and make it more acidic. However, tomatoes are happy in slightly acidic soil. 


Knowing that my cousin Parsimony collects large quantities of grounds from coffee shops each evening to use for mulch, I decided to ask her how much would be too much. She told me stunted growth and blossom-end rot on the tomatoes would be an indication. Parsimony mulches her azaleas, camellias and hydrangeas very heavily but goes more lightly on tomatoes and plants that like neutral soil. She does not use the grounds at all on peonies, lilies or other plants that like a more alkaline soil pH. 


Another usually discarded food byproduct she uses is eggshells. She fills eggshell halves with soil, plants seeds in them ― avoiding the cost of expensive peat pots ― and puts them directly in the soil when the seedlings are ready in spring. In summer, she adds washed and well-crushed eggshells to the coffee grounds she spreads on her tomatoes. She surmised that your son might be able to pulverize them finely in a coffee grinder. Eggshells sharpen blades, and some people even toss in bits with coffee while it’s brewing to give it a smoother, less acidic taste. However, you wouldn’t want to swallow sharp pieces of shell, and a fine grind will biodegrade much quicker in the soil.  


The real danger of the soil eventually becoming too acidic is that it would inhibit the intake of calcium. This would result in the blossom-end rot mentioned by Parsimony, a disorder that can spoil part of a tomato. It’s not a fungus or bacteria but the result of nutritional deficiency. Eggshells not only provide calcium, but elevate the soil pH to facilitate its absorption. Additionally, when raked into coffee grounds, the roughly textured eggshells keep them from caking into an impermeable irrigation barrier.


Periodically, Parsimony will also mix in some compost. She advises your son and his friends to start collecting grass cuttings and leaves, and throw in fruit and vegetable scraps. Some of these scraps, such as banana peels and apple cores, can be dug directly into the soil, but citrus fruit peelings have to go into a compost pile first because until they are broken down, they will repel, rather than attract, earthworms.


Parsimony also noted that your son and his friends eat pizza, and because she hates waste so passionately, she wants them to know they can put the empty pizza boxes out every Monday morning in a trash can or brown paper grocery bag for the City of Hyattsville to pick up. Pizza boxes are among the items that don’t go into regular recycling but that can be composted by the county. For more information about this program, which also includes the collecting and composting of fatless meat scraps, bones and garden waste you don’t choose to compost yourself, just go to


I hope you will come to the next meeting of the Hyattsville Horticultural Society (, which is cautiously scheduled for October and will be open to anyone who is vaccinated. There will be specifics in next month’s column.