Garden Plot: All about bats and bulbs

Many people, restricted to home due to the coronavirus pandemic, are gardening in an effort to stay productive during this time.

Houseplants or habaneros — it’s too early to go out

Mary Ann in Hillandale, Maryland, writes: “When is it safe to put my houseplants outside on a screened porch?”

Most houseplants are tropical in origin, so the answer is the same as it would be for our favorite plants of summer, such as tomatoes, peppers, cucumbers and melons — and that’s when nighttime temperatures are reliably in the 50s.

Temperatures in the high 40s, such as 48 and 49 are fine — but it’s risky to go any lower.

Despite the perception that summer has already appeared, we recently had nights with temperatures in the 30s in the heat-sink of D.C. and that means frost in some of the surrounding suburbs.

So here’s the deal: Wait until May, check the 10-day forecast and if all the upcoming nights are in the 50s or high 40s, go for it.

Holy Bat-Poop, Batman!

Sina in Front Royal, Virginia, writes: “We recently installed a bat house on our property with hopes that the little dudes will help cut down our mosquito population and that they will be fun to watch from our yard in the evenings. I’ve read about bat guano being an amazing fertilizer but wanted to get your opinion since they are technically ‘meat eaters’ and your article on animal manures states that those are a big no-no. Any advice on collecting and using guano once our new residents move in? Or should I avoid it altogether?”

Bats are bug eaters — like free range chickens, ducks and such — and their guano is highly prized, although it can be very high in nitrogen.

The best way to capture it is to have a bin of shredded leaves underneath their home and mix it all up every once in a while.

Now, about those hopes that bats will eat mosquitoes…

The real ‘Batman’, Dr. Tom Kunz, Professor of Biology and Director of the Center for Ecology and Conservation Biology at Boston University, where the Kunz Bat Lab is named in his honor, explained the concept that bats eat lots of mosquitoes is a mistake based on a 1960s-era lab experiment using fruit flies.

Although bats do eat a few mosquitoes, their main diet is big, fat, juicy moths — almost all of which would have given birth to agricultural pests like the tomato hornworm, corn earworm and almost any other caterpillar that attacks crops.

So bats are great to have around vegetable gardens, but dragonflies are the mosquito eaters.

Not all bat houses make a respectable bat cave

Many bat houses go unoccupied because they’re too small, not placed high enough or are not near a source of fresh water.

Bats need to be able to move up and down inside the box during hot days and chilly nights to regulate their body temperature — so the bigger the better.

Bats are also very social and like to nest in large groups.

They need a long, straight drop out of the bottom to exit safely — and they would greatly prefer a habitat shaped more like a big martin house than a “box.”

It should be up on a pole to keep predators out, etc., etc.

Several years back, I interviewed a number of experts and wrote a very detailed article about bats and their needs for my public radio show, You Bet Your Garden.

Spring bulb procrastinator of the year!

Dot in Frederick, Maryland, writes: “I have bulbs that I purchased in the fall but didn’t plant. Some of the bulbs have started to sprout. Can I plant them now?”

Well, you can try — and if you are lucky — you will get leaves, but the flowers deep down inside those bulbs have not had the chilling hours required to produce the flower stalk that the flowers would otherwise have risen up on.

And you are really late — daffodils and crocus are long-done flowering and area tulips are wide-open and almost finished.

Although they’re called spring bulbs, you are supposed to plant them in the fall!

If you have a spare fridge in which no fruit will be stored, you can try and force them out of season.

Plant the bulbs in containers filled with potting soil, saturate them well with water and place the containers in a fruit-free (ethylene gas released by the fruits would ruin the bulbs) fridge.

A minimum 16 weeks for tulips, 12 weeks for other types.

Bring them out in September (any earlier and they would burn up in the summer heat, spring bulbs are cool-weather lovers), water well and, perhaps, amaze your friends and neighbors!

Mike McGrath was editor-in-chief of ORGANIC GARDENING magazine from 1990 through 1997. He has been the host of the nationally syndicated public radio show “You Bet Your Garden” since 1998 and WTOP Garden Editor since 1999. Send him your garden or pest control questions at

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