(iStock)

The catkins are piling up — those pendulous clusters of tiny flowers covered in pollen. They’re heaped on the side of the road, all over your driveway, and lodged into the little space between your car’s hood and windshield. It’s annoying, but it’s also a sign that tree pollen season is over.

Hallelujah.

In oak trees, which have been our main source of tree pollen over the past couple of weeks, catkins are the male reproductive organ. The catkins shed pollen through the wind, and, ideally, that pollen fertilizes the female flowers. When the catkins are spent, they drop to the ground.

Tree pollen maxed out at 2,828 grains per cubic meter on Wednesday.

“This was right in the midst of the heat wave with sunny, dry and hot days that made for perfect conditions for pollen release,” said Susan Kosisky, chief microbiologist at the U.S. Army Centralized Allergen Extract Lab.

Since then, pollen has been on a slow decline, despite still being “high” for the Washington region. On Sunday, the lab measured 570 grains per cubic meter of tree pollen, but it climbed to 926 on Monday. Even though things are getting better — it’s just a third of what it was last week — trees are still churning out the yellow pollen. Oak, mulberry, sycamore, pine and walnut are all adding to the counts right now.

What we really need is rain.

“I was hoping for some rain this weekend to wash the pollen off of cars, outdoor surfaces and the leaves of the trees,” Kosisky said in Monday’s update. “This helps to keep all that pollen from recirculating into the air along with additional pollen release.”

Trees produce the biggest spike in pollen, which makes this the worst season for allergies. But many people are allergic to grass, too, and unfortunately, grass pollen tends to ramp up as trees are winding down — from late spring to early summer.

According to the American College of Allergy, Asthma & Immunology, allergies to grasses are very common. They can show up many of the same ways tree allergies do, “including nasal symptoms (runny nose, stuffiness, sneezing), asthma, and eye symptoms (itchy, watery/red eyes). People can also have skin rashes (hives or skin welts) after exposure to grasses, but this is much less common.”

On Monday, grass pollen was in the moderate range at 6.39 grains per cubic meter, and it will probably continue to rise over the next several days.

You can fight grass pollen just as you do other outdoor allergies: watching the pollen count, staying indoors when possible and employing whatever allergy relief treatment works for you. If you’re having trouble finding something that works, a couple thousand readers chimed in last week to share their secrets.