Lawn care: Never aerate cool season lawns in spring

About a third of an apple tree\'s branches should be removed in any given year, says WTOP Garden Editor Mike McGrath. (Thinkstock)
Cycle of lawns: Preparing for another year of lawn care

wtopstaff | November 14, 2014 5:40 pm

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Editor’s Note: Mike McGrath will appear March 15 – 17 at the Fredericksburg Home and Garden Show at the Fredericksburg Expo Center.

Mike McGrath,

Most local lawns should be aerated only in the fall

Carole in Columbia, Md. writes: “I bought a Groupon for lawn aeration and over- seeding last summer, but when I tried to make an appointment the company said they were way overbooked (they said they didn’t expect such a big response to their Groupon). Now they tell me that they’re making appointments for the first week in March. Is that really a good time to aerate and seed my cool-season lawn? Or should I ask them to honor the Groupon in the fall?”

Cool season lawns like bluegrass and fescue should never be aerated in the spring or summer, Carole. Although it does relieve soil compaction, aeration (removing small plugs of grass and dirt) stresses the turf a bit, and lawn owners should avoid any extra stress as our lawns get ready for the summer swelter. That’s why aeration should only be performed in the fall. Cool-season lawns are at their strongest going into the cooler weather, and aren’t stressed by aeration then.

Note: The opposite is true for warm-season grasses like zoysia and Bermuda. They should be aerated in the spring — right after they green up fully for the season.

And, sowing grass seed in the spring is useless with cool-season lawns. Aug. 15 through the end of September is the only rational time for bluegrass, rye or fescue seed to be applied.

So either get a delay until the fall or ask for a refund.

Timing corn gluten and grass seed

Scott in Springfield writes: “What’s the best way to time the use of grass seed and corn gluten in my lawn so I can maximize the benefits of both?”

Well, there’s really no conflict in the spring, Scott. Although stores will eagerly sell you grass seed in the spring, the soil stays too cold for too long to achieve good germination, and then summer’s heat burns up any young grass that does sprout. So feel free to spread corn gluten meal when local redbuds and forsythia burst into bloom. It’ll feed your turf and prevent crabgrass and other warm season weed seeds from sprouting.

The fall is when the timing does gets tricky. It’s important to feed cool-season turf in the fall, but mid-August through September is the ideal time to sow grass seed — and corn gluten meal would prevent the seed from sprouting. As would a chemical pre-emergent. Chemical or organic, pre-emergent herbicides prevent all seeds from successfully sprouting.

So if your lawn needs some seed, hit that August-September window and use a different fertilizer in the fall, an inch of compost or a nice bagged organic fertilizer that’s specifically labeled for use on lawns.

What about corn gluten on zoysia grass?

Harry in Arlington writes: “I have a zoysia grass lawn that gets infested with spurge in the summer. I understand that the only way to control this weed is with a pre-emergent herbicide, but I don’t want to use one that will harm the zoysia. I just want to stop the spurge. Do you have any suggestions?”

Absolutely, Harry. Spurge is a summer annual weed just like crabgrass, so apply corn gluten meal to your lawn just as the local redbuds and forsythia begin to bloom this spring. The natural pre-emergent activity of the corn gluten will prevent any lurking weed seeds from sprouting.

Then, to keep your warm-season zoysia grass healthy, apply corn gluten again in the summer, after your zoysia has been green for a full month. Unlike cool season lawns of fescue and bluegrass, zoysia and Bermuda should be fed in the summertime.

Don’t give boxwood Holly-tone — or any acidic fertilizer

Gina in Bowie writes: “I have four well established English Boxwoods in front of my house. Last August they turned a rusty, reddish color — almost like leaves changing in the fall. What do you think can be the problem? I feed them twice a year with Holly-tone, mulch them twice a year and water a lot in the summer.”

That’s three strikes on you, Gina. (And it’s just “boxwood”, no matter how many of them there are. In other words, the plural of boxwood is boxwood.)

Now, although Holly-tone is a natural fertilizer, it also acidifies the soil, and Lynn Batdorf, curator of the Boxwood Collection at the National Arboretum, explains that boxwood requires a slightly alkaline soil. So raise the soil pH with a dusting of lime or wood ash — after you remove all of that uber-mulch.

That’s right, your heavy mulching is also harming the bushes, as boxwood has shallow roots that prefer to be un-mulched. If mulch you must, keep it to no more than an inch deep, and make it a mulch of compost. That’s all the food that boxwood requires.

And, stop watering so often! If water you must, one deep, long soaking once a week should be the maximum.

Prune AND thin the fruits to get great apples

Dan in Bethesda writes: “I have a 27-year-old apple tree that didn’t get pruned last year, and the inner growth has gotten out of hand. How should I prune this apple tree? If the squirrels don’t get them first, I get a nice harvest of small apples in early to mid-August.”

It’s really easy, Dan. Anytime between now and when the tree begins to flower, remove lots of entire branches. Take these mostly from that crowded center of the tree, but also take off any branches that will restrict airflow inside the canopy. You can — and should — remove a full third of an apple tree’s branches in any given year.

Then, when the fruits begin to form, remove three-quarters of the developing fruits while they’re still tiny and you’ll enjoy full-sized apples this August. You get the best apples when you remove most of the fruits early in the season.

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