Garden Questions Answered — Empress of Dirt

Answers to garden and garden art DIY questions submitted by readers of the Empress of Dirt newsletter.

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Your Garden Questions Answered

When I get more questions than I can fit in the mailings, I’ll do my best to answer them here.

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90. If I plant different colored irises together will they stay true to their colour or morph to the dominate one ?

Irises do not change color. You can plant as many different colors side by side as you like—they’ll stay true to their original hues. But there’s more to the story.

What can happen is that certain varieties may be more vigorous than others. Over time, the stronger growers can take over, making it seem like your irises have changed color when in fact only one variety is dominating the bloom that year.

Some types of iris, including bearded irises, may not bloom every year. This can also create the illusion that colors have changed, when it’s simply a matter of which plants are flowering and which are taking a break.

While cross-pollination is possible, it would only affect the next generation of plants grown from seed—not the color of your existing irises.

89. How can I know what type of mint I’m buying at the grocery store?

The mint sold at the grocery store is usually spearmint. You can try photographing the leaves at the store and asking Google Lens to identify it. But typically it is spearmint (sometimes labelled as “sweet mint”) and not peppermint which has a bolder taste and armona that many do not like for cooking. It would be nice if plants were always properly labelled but these things tend to be mass produced and labels only supply information required by law.

88. Does fertilizer have a shelf life?

I checked with several brands and they all say the same thing. The plant fertilizer products we buy for home use have no specific best before date or use by date so long as they properly stored.

Proper storage includes:

Keeping the product in its original container with a tight lid in a cool location.
Avoid exposure to high humidity, water, and temperature fluctuations.

Do not use if:

Any signs of mold, unusual odor, bugs, distorted appearance.

Older products may be in cardboard containers that did not protect the product from exposure to these things.

The problem with using altered fertilizer is you cannot know the efficiacy rate. The application instructions on the label may not deliver the desired dose but we have no way of knowing.

When in doubt, start fresh.

87. I’m an organic gardener. How can I stop snails from destroying my vegetables?

Everything I know about slugs and snails and how to outsmart them is here: Dealing With Slugs & Snails Without Harming Your Garden.

86. Where can I find a good resource to design a layout for a garden bed?

Hello! Would this be for a vegetable garden or perennial garden?

For vegetable gardens, the book Week-by-Week Vegetable Gardener’s Handbook is helpful. I also have an ebook, Growing Vegetables: A Weekly Indoor & Outdoor Seed Sowing Plan for Beginners that shows how and when I sow from late winter to fall.

For other plantings, I’m sure you know there are a lot of general resources (sites, books, apps) available but what works is so dependent on your conditions (soil, water, light, location, climate) and plant preferences that there’s probably always going to be some custom planning required.

I realize this isn’t very helpful but feel free to ask a more specific follow up if you like.

85. What is double digging and should I do it?

Double digging is a (supposed) soil improvement method that was commonly recommended to gardeners in recent decades. The idea was that you could improve your soil by adding soil amendments by deeply turning the soil (double the depth of the shovel head) to incorporate them.

What I learned from double digging (back in my early gardening days) is that it’s naive to think you can change the underlying nature of your soil. There’s just too much of it.

In my case I had heavy clay soil and was advised to add compost and peat to “loosen” it up. In reality, any benefits are shallow and temporary (and therefore a waste of money) because all the new materials disappear as the seasons go by.

I eventually realized that, if I wanted better soil, I should build up with compost and manure and organic “waste” on top of the poor soil instead (without digging). This gradually creates a whole new, better growing layer. It’s an approach that works very nicely and I now use with my current sandy soil garden as well.

84. Is it ok to water houseplants with ice cubes?

There isn’t a lot of research on it but the gist seems to be that the cold probably won’t be an issue but the amount of water the melted cubes provide is likely too little for many plants. In other words, it could result in under-watering. This explains more in detail.

83. What does “days to maturity” mean?

Days to maturity tells us how long it take the plant (in typical, favorable conditions) to reach its maturity or harvest date. It’s an estimation to assist with our timing. Seed companies are getting better at listing how they calculate it on the packets. This explains the two main definitions depending on whether you’re starting from seed outdoors or transplants.

82. How can I discourage voles in the garden?

This is one of those questions that comes up a lot and I don’t think there is a satisfying answer. If we start with the premise that we’re here to support the ecosystem, harmful “solutions” are not an option. I can tell you the typical responses, but they are all either aspirational or perhaps not realistic.

One of the best long-term strategies is to encourage natural predators like owls, hawks, and even garter snakes—adding a raptor perch or leaving some wild areas nearby can help. This is likely not an option in an urban or suburban garden and we can try to attract these species but they have their own agendas.
You can also make your garden less inviting by keeping grass trimmed, removing brush piles, and using less mulch around plants.
For prized trees and shrubs, try using hardware cloth barriers underground to protect roots. But long-term, this will be very hard to maintain.
Some gardeners use castor oil-based repellents or plant vole-resistant species like daffodils, but results vary and it seems unrealistic to keep up with it.
In some cases, it may be easier to accept a bit of damage—vole tunnels often disappear on their own by late spring, especially as predator populations catch up.

81. What should I do with potted tulips after flowering?

Flowering bulbs get confusing because there are many varieties and there’s no guarantee they’ll bloom again next season.

This explains in greater details which spring flowering bulbs are likely perennial and which should be regarded as annuals.

If you want picture perfect flowers, plant new tulip bulbs each fall.

If you don’t mind less than perfect flowers (or the risk of no blooms), continue growing old bulbs and see what you get.

After flowering in spring, you can remove the stem and old flowers but not the leaves. The leaves gather energy for the next flowering cycle and that takes a number of weeks.

When the leaves have browned and withered away, you have a few options.

Plant the bulbs in the ground (unless squirrels are watching)
or
Remove them from the potting mix and wrap in newspaper or repot them in fresh potting mix and keep them in a cool (ideally 50°F / 10°C or a bit lower), dry location. In fall, you can plant them in the ground or overwinter them outdoors in containers. Exposure to winter cold is essential for bulbs that require a cold period (for many weeks) to facilitate spring flowering.

Whenever buying bulbs, check if it should bloom more than one spring. Typically, special tulips and daffodils (fancy hybrids) tend to be one and done while other bulbs like species tulips and snowdrops which naturalize (spread through the ground further and further each year) last for eons.

This bulb planting guide has more tips on best practices.

80. What can I do with leftover seeds from previous years?

Sow them (and expect lower germination rates) or give them away (letting recipients know what year they are from). You can also test them using these tips.

79. Did you know earthworms are attracted to (and eat) banana peels?

Yes.

78. How do you grow a lemon tree from seed?

I have a complete tutorial here: How to Grow Lemon Trees from Seed (& Other Citrus Fruits). You can use this tutorial to grow lemon, orange, tangerine, kumquat, and more.

77. Are coffee grounds good for the garden?

I see contradictory information about using coffee grounds in the garden. Could you get to the bottom of this and give us the real, er, dirt?

The benefits of coffee grounds are greatly exaggerated but they are fine as a normal part of composting. See What to Know Before Adding Coffee Grounds to Your Garden for the complete scoop.

76. Is there any truth to using copper tubing in your garden to help your plants grow?

No.

75. How can I stop insects from biting while I’m weeding?

I probably don’t have an answer you haven’t already thought of and many common suggestions have drawbacks.

Your question isn’t specifically about mosquitoes but that’s something I have to think about because I get allergic reactions to the bites so it’s a good example.

Last year mosquitoes were so prolific in my region that I resorted to wearing head-to-toe protective clothing including a mosquito head net. It wasn’t really convenient but it did help.

Sometimes a pest is more active at a particular time of day or in moist conditions so I work around that too.

If you are thinking about other tactics, there are plenty of myths about repellents. This article has some details on what does and does not work.

Ultimately, if for some reason some insects are really pesky, I just wait it out. All things must pass. And it’s not worth trying anything that could harm the ecosystem in the process.

I wish there were more (safe for all) solutions.

74. Where can I get seeds in small quantities?

This article on 10 Easy Ways to Cut Costs on Garden Seeds has lots of tips. Whether you want to save on costs or simply don’t want surplus, the tips are the same.

73. Can you propagate boxwood from cuttings?

Yes. See answer 14 (scroll down) for details.

72. Why are my Brussels sprouts only growing leaves and stems?

Check your seed packet to see the typical days to maturity. Some are very slow growing. If growing conditions are optimal, that’s the most likely reason.

I sometimes grow them in a part of my garden that is almost always shady. That really slows things down, taking many months longer than expected in addition to a winter growing hiatus.

71. What can I plant during warm spells during the winter?

This is a bit tricky because a warm spell followed by more frosts (sleet, rain, snow) isn’t going to jump start the garden.

An exception could be seeds that need cold moist stratification, assuming there will be an adequate number of cold days between sowing and last frost (to suit that particular plant).

If spring fever is severe (I feel it every single year!), you could experiment with sowing in pots so you can control their weather exposure in the weeks ahead (by covering them or moving them around). Just be sure to choose seeds recommended for direct sowing outdoors before last frost.

70. Can I overwinter ferns indoors?

Every so often I receive a question that sends me down a giant rabbit hole and this is one! There are so many different ferns—from all over the world—with different tolerances and needs—which means the answer is it depends.

The first step is to find out what type of fern you have. Once you know the name and its natural climate, you’re set. I have ferns here in my cold climate garden that won’t even tolerate transplanting. Others commonly grown as houseplants or potted plants may tolerate a transition to indoor life for the winter. The trick with all overwintering is to do it when outdoor and indoor conditions are most similar (so the plant barely notices).

See if you can identify your fern (or maybe you already know it’s botanical name). From there you should be able to find overwinter recommendations online.

69. When and how should I prune my raspberry plants?

I wish there was a single answer but there is not. It depends. But here are some general guidelines.

For any woody plant, it’s fine to remove dead, damaged, diseased, or crowded branches at any time.

For raspberry plants, pruning is often preferable but still optional. This can happen in spring or fall.

If you know the variety name, look up the recommendations for your specific plant or check the plant tag.

If you don’t know which variety you are growing, it’s fine to leave it alone for the next two growing seasons and learn through observation. Take photos and make notes.

New plants may not produce flowers or fruit until year two.

Here are a few tips:

Canes start out pliable and green (= new growth) and over time become brown and woodier (= old growth).

Pay attention to see where flowers and fruit form — on which branches, when, and how often.

The goal is to avoid cutting anything that is yet to flower and fruit other than trimming back canes that are too long to manage. A length of around 1.5 meters (or yards) is fine.

Pruning (cutting back down to 6″ above ground) should wait until after the cane has produced fruit.

If you live in a snowy area, it can be advantageous to hold off pruning old growth until after winter. Those canes can be good at supporting snow for insulation.

I don’t have a full guide on pruning raspberries but I do have this information on transplanting along with some care tips.

68. How long will leaves preserved in beeswax keep their color?

I’ve wondered this myself. It seems to depend on the condition of the original leaves and heat or light exposure they have once preserved.

I’ve got some that have lasted years with no sign of fading while others have seen better days.

67. Can you overwinter coleus in a cold garage?

Coleus are not very cold tolerant. If you can keep the soil and air at 60°F (15°C) or warmer, it may work. I’ve done it by putting the pot in a plastic bag and packing it with straw but there are no guarantees, of course.

Besides bringing them indoors as houseplants, you could instead root cuttings indoors for planting next year.

66. How can I mitigate a (insert any insect name here) infestation?

I realize this is not what some want to hear or how they want to do things but I garden ecologically and that means—for the long-term greater good—accepting that every gardening season will have hits and misses, highs and lows, bounties and disappointments.

That is all to say, all things must pass. I just accept what each year brings and let nature sort itself out without any collateral damage.

65. My plants are not liking this excessive summer heat. What are some ways to provide shade?

I have the same issue—recent summers have been intense. You could gain shade by blocking the sun with other tall plants, fencing, trellis, arbors, or hanging shade cloths.

64. My (insert any plant name) has yellowing leaves. What might it need?

That’s not something I can judge from afar. Leaves can yellow for countless reasons—some expected, others due to stress: it’s time to shed leaves, overwatering, underwatering, poor nutrient uptake, plant needs repotting, too much light, low humidity, too much heat near the plant. Hopefully you’ll look at this list and determine what resonates with your growing conditions.

63. How do you overwinter Mandevilla?

There are two options: move it indoors and care for it as a houseplant for the winter or keep it dormant in cool—not cold—(50°F/10°C) storage.

62. How do you take cuttings from fig trees?

You can take cuttings using this tutorial: 40 Shrubs and Vines to Root from Hardwood Cuttings (Tutorial)

61. Something keeps eating my freshly-sown peas. What is it?

If the damage happens below the ground, it could be mice or voles.

To get around the issue, plant in containers and use hardware cloth screens and cloches to keep animals out. My garden is a wild kingdom so I have to grow just about everything this way.

60. Can you store coleus indoors for the winter?

Yes but act early because they are tender plants. The article below explains how to prepare your plants for life indoors as houseplants.

59. Can I keep gravel weed-free without using pesticides?

Your best bet would be to improve what’s below the gravel either with industrial strength weed barrier cloth (like the ones used in professional greenhouses) or compressed layers of different sizes of crushed gravel (below the “good” layer) the way pros do it.

I have brick walkways and I remove the weeds using a steam cleaner. Perhaps that’s an option too.

58. Do tomato fruits need direct light to ripen on the vine?

No. They need light to grow but not to ripen.

Tomatoes can ripen if:

The fruit is physiologically mature (typically reaching the listed “days to maturity”).
The temperature is not too low or high: 60°F to 90°F (15°C to 32°C) during day and between 50°F (10°C) to 70°F (21°C) at night.
No drought or humidity issues.
Nitrogen is not too high.

The reader mentioned his plants are growing in dense vines. Ripening is possible if the above items are fine. If there’s any sign of disease, I’d trim away some stems for better air flow.

Read more: How to Ripen Tomatoes (see section on Reasons Tomatoes Will Not Ripen)

57. Do canna lilies need a frost before digging them up?

Yes. Let them die off from a frost before winter store. It’s the same preparation and storage that dahlias like.

56. I tried rooting a pineapple top but it rotted. What went wrong?

I wish I could troubleshoot from afar but there’s too many possibilities. It could be that the fruit the top came from was too ripe, or any number of indoor conditions were not right in the moment. I suggest comparing your growing conditions to the ones recommended in the article to see if you can find something to tweak. From there, try again. Try several. Keep going. If you do not give up, you will eventually succeed.

55. How do you overwinter tuberous (aka “non-stop”) begonias?

According to the American Begonia Society:

Stop watering in autumn when the plants drop their leaves and yellow.
After first frost, dig up the tubers (leaving any remaining plant parts in place), gently remove all soil, roots, and any rotted parts.
Dust with a fungal powder or sulphur and lay tubers out to dry (do not allow to freeze). You can tell they are dry enough when the stems readily break off the tubers—and you do want to remove them now.
Place each tuber in a small (labelled) paper bag and store in a cool (not freezing), dark location until spring planting time.

Begonias you can grow as houseplants:

Rhizomatous begonias
Cane type & bedding begonias
Rex begonias (like high humidity)

54. Can you get rid of soil gnats with hydrogen peroxide?

The research is iffy. One thing that can stop adult gnats is these yellow sticky traps (Amazon). The article discusses more tips.

53. My squash plants were large but didn’t fruit. What happened?

I had a few questions like this one—some mentioned there were flowers but no fruit, others said they never flowered.

There can be one or several of these reasons: too much heat, something ate or removed the flowers, too much fertilizer—specifically the nitrogen, and/or no pollination.

52. Can you grow marigolds from cuttings?

Yes, 12 Flowering Annuals You Can Grow From Cuttings has a list of popular annuals that can grow from stem cuttings and marigolds are on the list.

If you’re like me, it’s always hard to remember or tell which plants can grow from cuttings so it’s helpful to keep these lists handy.

51. I have an oversized cardboard cylinder. I want to add stones and glass on it. What’s the best glue or do I need to use something else?

I think success will depend on how tough the cardboard is. It’s possible the weight of the stones and glass may gradually tear away the cardboard—or it might succumb to water exposure.

My go-to adhesive is always GE II Silicone Sealant -Amazon (clear, waterproof, suitable for outdoor use).

If it’s a project for indoors, you may be ok. Outdoors, I’d be tempted to first protect the cylinder with an outdoor primer (Amazon) first. Then sand it and use the sealant as glue.

Please let me know what you do and how it goes.

50. My tomato plant has flowers but no tomatoes? It is very healthy but it’s been hot.

Your hunch is correct—it can be too hot for tomatoes to produce fruit. Other reasons include failure to pollinate or too much nitrogen (typically from too much fertilizer) in the soil.

If heat from direct sun is the issue, see if you can create shade around the plant. Sometimes it’s too late, other times the plant rebounds and produces fruit.

I grow all my tomatoes in large containers for this reason—I often need to move them around when there are heat waves or too much rain (which causes the fruit to split open).

49. How do you overwinter cannas (canna lilies)?

You can store them in a cool, dark place just like dahlias using these instructions:

48. I need recommendations for planting around headstones at a cemetery.

First, if you haven’t already, check if the cemetery has guidelines for plant choices. Some will have specific plant recommendations or restrictions or at minimum describe how much space is available for the full-grown plants.

If you have free choice, I’d think about what’s suited to the climate and growing conditions (including sun exposure, soil type, and water), whether you want annuals or perennials, and how much maintenance is required.

Ideally you find plants that tick all those boxes and bring welcome memories of your loved ones.

47. Can you grow lilies from cuttings?

No. The best way to propagate a favorite lily is to divide the original plant (specifically the bulbs which are underground) and transplant it.

This lists 12 Flowering Annuals You Can Grow From Cuttings.

46. I’m looking for screens for sorting seeds.

I assume you mean you want to sort and clean seeds you have collected? It’s something I’ve never written about because it gets complicated. Depending on the seed type, different screens or other equipment work best.

It’s not a solution but this article at seedalliance.org describes the process in more detail.

Personally, I keep each type of seed in paper bags and basically remove the debris by hand. For this reason, I do not have screen sources to recommend.

45. Do you have any information on sprouting pineapple?

Yes, this explains how to grow a new pineapple plant from a pineapple top.

This explains how to grow a pineapple plant from seed. The catch is, it’s very difficult to get viable seeds.

44. How and when do I clean out my birdhouses?

I know some of this is obvious… The time to clean out a nesting box is when it is not in use. It’s very helpful to determine which species is using the box and read up on their habits—how many broods might they raise per year and will they reuse the same nest?

I have wren nesting boxes and they will raise several broods back-to-back in the same box. By late summer they are done. I double check by opening the hatch where it’s obvious that the remaining nesting materials have not been used in a while.

If you have an automated wildlife camera, you can also use that to monitor the box over a few days to be certain the birds have moved on.

This is all to say, generally by late summer or early fall, mating is done for the season and you’re free to clean out debris (old nesting material) and clean the container.

Some birds like to use nesting boxes in winter as a sheltered resting spot so be sure to keep it available.

43. I use straw mulch. Should I dig it into my hard soil at the end of the season?

I wouldn’t dig it in. Depending on conditions, it could take years for the straw to break down.

Instead, because the soil is hard, I’d rake off the straw, add an inch or two of compost, and put the straw back in place. By doing this year after year, you’ll gradually build better soil.

The idea is, when the soil is not great, instead of trying to change it, build up over time.

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9. When growing a variety of fruit trees, how do you get the pH level right for each type?

Unless you grow in containers where you have control over the soil, you can’t have custom pH levels around each plant.

Also, soil pH can’t be permanently changed but instead requires ongoing amendments.

Realistically, your soil is what it is and it’s best to plant what it likes. Or, as mentioned, grow in containers and, if you can, provide the soil conditions each plant prefers.

8. The pH for my blue hydrangea is above 7, but they bloom blue. They are endless summer type. I don’t understand why they aren’t pink. Any ideas? I tested with a pH monitor, and the vinegar method?

It could be that your pH monitor is incorrect—they are not known for accuracy. Soil pH strips are more reliable. Also, some varieties cannot shift color. Plus, the vinegar idea is a myth and does not work.

7. How do I know when it’s time to “pot-up” my seedlings? And can I skip that step if the weather is settled and I can plant them out?

Indoor seedlings need potting up (transplanting to a larger pot) when they are outgrowing their current pots. Signs include the potting mix drying out quickly (requiring watering more than once a day), roots growing out the bottom drainage holes, or stunted growth.

It’s fine to skip potting up if outdoor conditions are right for planting. That said, I would still always harden them off (gradually transition them to outdoor conditions) prior to planting out.