Pollen, Allergies and Plants

Posted on Tuesday, March 2, 2021 · Leave a Comment 

If you suffer from spring allergies, this would be a good time to know what plants are affecting your comfort. Right now, many trees are dumping their pollen. Most trees are wind pollinated and produce lots of pollen. They depend on the wind to move pollen around – and up your nose. 

 

Male pollen producing pussy willow flowers on left with female flowers on right

Although some trees and shrubs produce both male and female flowers, many are dioecious, meaning that male and female flowers are on separate plants. It is thus to their advantage to produce their (insignificant-looking) flowers and lots of pollen before the leaves get in the way. Which for me, is right now. Showy flowers do not necessarily mean that trees like catalpa are low on the aggravation index (they are rated 8 of 10 on the index), but others like magnolias are lower. Both of those are pollinated by insects.

 

Of the trees, male poplars are among the worst – and in my area, they are just starting to bloom. Other culprits include willows, birches, oaks and some maples, but not all. If you are buying trees, look for trees that have separate male and female plants (as opposed to both on one). Always buy the female specimen if  you can, as it is the males that produce the pollen, and cause the allergic reactions. Not all plant tags will tell you if the plant is male or female, but good nurseries may know.

 

Hakuru nashiki willows do not produce blossoms or allergic reactions

Very popular in the landscape industry right now is the ‘Hakuru nashiki’ willow. It has tri-colored (green, white and pink) leaves in June, and is sold either as a multi-stemmed shrub or as a “standard”. Standards are created by grafting branches on the top of a straight, bare-of-branches stem that is generally about 4 feet tall. As far as I know, Hakuru nashiki willows are all female, so they do not create those fuzzy “pussies” and pollen.

 

Want a nice pussy willow ( Salix caprea)? Not all are bad for the allergy-prone. It is worth consulting a book like Tom Ogren’s “Allergy-Free Gardening” that lists trees and flowers species-by-species, (and often with cultivars) with their potential for making you miserable. Ogren’s book lists ‘Weeping Sally’ as a pussy willow with the lowest rating for causing allergies, while the male forms of white willow ( Salix alba) are  among the worst rating. Even so, many of the males are sold as named cultivars for decorative purposes.

 

Not all pollen is created equal. Each spring I notice all the yellow pollen dropped on my car by pine trees. Pines produce huge amounts of pollen, but it is waxy and not very irritating to your nasal membranes. And it’s heavy, so it doesn’t fly far.

 

Catalpa blossoms are showy and insect pollinated but still can cause hay fever

After the trees do their thing, along come the grasses. The seven worst offenders are introduced species of grass, including orchard grass, blue grasses and timothy grass, which is commonly grown for animal feed. Grasses are wind pollinated, and their pollen can float long distances. Your lawn should not be a problem so long as you never let the grass get tall enough to blossom. But fungal spores in the lawn can cause allergic reactions, and can be stirred up by mowing, so if you get hay fever, you have a good excuse to get your spouse or kid to do the mowing.

 

Flowers with flashy form and generally are not significant allergy-producers. Tulips, delphinium and peonies are obviously trying to get attention. They are the flirts – and insect pollinated.  Others such as hostas are among those least likely to cause an allergic reaction.

 

According to Lucy Huntington in her book, Creating a Low-Allergen Garden, members of the daisy family have flowers that are insect pollinated, but their pollen is highly allergenic to most sufferers. Chrysanthemums, asters, marigolds and zinnias can bother folks with allergies. I suppose that is particularly the case if you enjoy sniffing their scents. She also suggests avoiding geraniums (Pelargonium hybrids), strawflowers, dahlia hybrids, foxglove, sunflowers, nicotiana, and cosmos.

 

Huntington’s book is full of lists and suggestions for low-allergen plants. Here are some of her suggestions for plants suitable for people with pollen allergies:

 

Annuals: Snapdragons, petunias, annual phlox, scarlet sage (Salvia splendens), purple salvia (S. farinacea), pansies, bacopa, California poppies, nasturtiums and verbena

 

Perennials: columbine, astilbe, bellflowers (Campanula spp.), bleeding heart, delphinium, daylilies, Siberian iris, peonies, oriental poppies, penstemon, garden phlox, Jacob’s ladder (Polemonium caeruleum), hollyhocks, alliums, globe flower (Trollius spp.), lady’s mantle, coral bells, catnip, hosta, foamflower (Tiarella cordifolia) and periwinkle (Vinca minor).

 

The good news is this: pollen is generally released in the morning, and by evening much of it has settled down, so evening should be a better time to garden. And rain knocks the pollen out of the air, so run outside and pull weeds after a nice downpour. You don’t have to cut down the culprits, and wearing a Covid mask will help if pollen is really bugging you!

 

Henry is a gardening consultant and the author of 4 gardening books. Reach him at henry.homeyer@comcast.net.

Filed under Article · Tagged with catalpa, hakuru nashiki willow, hay fever, pollen in plants

Planting a Tree

I fell in love this summer. With a tree, that is. The Northern catalpa (Catalpa speciosa) is a fast-growing tree that blooms beautifully in late June in my part of the world. The flowers, about 2 inches long and wide, are white with 2 lobes and purple or lavender stripes inside. They are deliciously fragrant. I got a 10-foot tall specimen at E.C. Brown Nursery in Thetford, Vermont.

It is very important to find the “trunk flare” before planting a tree. That is the lower part of the trunk that flares out above ground in the trees planted by Mother Nature. The flare is waterproof, but if buried in soil or mulch it will rot and the important cambium layer can be damaged, injuring the tree. When young trees are put in pots the flare is often covered by 3 inches of soil or more.

If not corrected, trees with buried trunk flare often die in 6 to 10 years because their trunks are essentially girdled by the rot. If you have a tree with a trunk that doesn’t flare at ground level, pull back some soil until you can see the trunk flaring out. Cut away the little roots you will encounter.

The hole should be wide not deep

It’s important to dig the hole for a tree the proper depth. You want to place the root ball on unexcavated earth so that it will not settle into a lower position that will fill in with soil or mulch, covering the trunk flare. The hole should be wide, not deep. I uncovered the trunk flare in my catalpa, which was just an inch or so below the soil line in the pot. There were plenty of small roots in that inch of soil I removed, and I just cut them away.

I also looked for roots encircling the root ball because it’s important to cut those back, and to tease out roots from the root ball before planting. I used my fingers to loosen roots at the edge of the root mass after removing the tree from its plastic pot.

Next, I measured the root ball. It was 16 inches wide and 12 inches deep. I dug a hole 3 times the width, and just an inch or two deeper than the depth of the root ball. I dug the hole with sloping sides down to the bottom. I used a hoe to scrape the bottom of the hole to make it flat.

As I dug, I placed the soil from the hole in wheelbarrows. One wheelbarrow was for topsoil, another for the poor-quality subsoil I encountered at the bottom of the hole. I was fortunate to find just a thin layer of subsoil – heavy clay, then sand beneath that. The sand will ensure good drainage.

Dig a hole 3x as wide as the pot the tree came in

If you have only a shallow layer of decent topsoil, you may want to replace some of the subsoil you encounter with topsoil that you purchase in bags. But don’t replace all your soil, even if it’s not of good quality. Mix topsoil 50-50 with the crummy soil only if most of the soil is of poor quality.

A teacher at Vermont Technical College once told me to imagine a tree as a wine glass sitting on a dinner plate. The wine glass is the tree we see, the dinner plate is the root system. So the tree needs to spread its roots far and wide. Creating a planting hole full of compost and rich topsoil will encourage the roots to stay in the original hole instead of spreading out. That’s known as the “bathtub effect.”

Make sure the tree is straight in all directions

To dig the hole the proper depth, I use a board (or a rake handle) to span the hole, measuring from time to time as I approached the proper depth. I dug down 14 inches for my 12 inch rootball, and in the bottom of the hole I added some of the better topsoil I’d dug up. I packed that down so it wouldn’t settle later.

Mother Nature does not use fertilizer when she plants trees. I don’t either. Fertilizers contain nitrogen, which stimulates fast green growth. But I want my tree to get established, spread its roots, and grow at a moderate rate. But I did add 2 mineral products that I bought in bags.

First, I added trace minerals in a mix sold as Azomite. It is a mix of some 70 minerals from volcanic and sea sources, mined and packaged in Utah. I have found it to add vigor and resistance to stress in plantings. The other product is called green sand. It is mined from a formerly undersea deposit in New Jersey. It is a good source of potassium and trace minerals. Potassium helps build strong cell walls.

I also paid attention to the north-south orientation of the tree when planting. Trees develop thicker bark on their south sides because they get more sun there. If a tree is planted with the north side from the nursery facing south at your house, the bark can develop sun scald in winter, crack, and damage the tree. Trees generally have more branches on the south side, so I planted the bushier side facing south.

Watering trees is important the first year, and even in dry times during the second year. I made a ring of soil around the tree to keep water from running away. And an inch or two of ground bark mulch will help to keep the soil from drying out.

Planting trees is not rocket science. Take time, do it well, and your tree will please you for the rest of your life.

Read Henry’s blog posts at https://dailyuv.com/gardeningguy.Reach him by e-mail at henry.homeyer@comcast.net.

Copyright © 2014 Henry Homeyer

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