Lawn and Garden Chemicals

Most folks walk into the chemical aisle, grab the bag with the prettiest grass on the front, and hope for the best. That’s how you waste money and sometimes kill a lawn. The right move is matching the product to the actual problem — and in cool-climate Montana, that means paying attention to soil temperature, the N-P-K numbers on the bag, and which kind of herbicide you’re actually buying.

Here’s the short version. Test your soil before you fertilize. Read the three numbers. Know whether you need a weed preventer or a weed killer, and whether it targets one weed or kills everything green. Get those three decisions right and the rest is just application.

Fertilizer: Reading the Three Numbers

Every bag carries three numbers — the N-P-K analysis. Each one does a different job. Nitrogen is important to a plant’s overall health. Phosphorus aids in developing strong root systems, as well as improves blooming, fruit growth and seed production, and helps increase disease resistance when used in the proper amount. Potassium promotes optimum plant growth and improves water retention and disease resistance.

Don’t buy on bag weight. Buy on the price per pound of actual nutrient — that’s what separates a good value from a marketing gimmick.

The synthetic-versus-organic question comes down to what you want. Fertilizers can be synthetic (inorganic) or made from organic materials, which are generally safer for humans, pets and the environment. Less-toxic alternatives like organic fertilizers, naturally derived fertilizers, compost or composted manure provide needed nutrients. Synthetic gives you quick, precise results. Organic builds long-term soil health. Compost and composted manure are balanced mediums derived from natural materials that provide both nitrogen and soil-enhancing properties. Leaving grass clippings on the lawn will likely provide the necessary secondary and micronutrients.

The single biggest mistake is dumping on extra nitrogen because you figure more is better. It isn’t. Excess nitrogen encourages blade growth at the expense of a strong root system, which weakens plants because the roots can’t keep up with top growth. It may also lead to nutrient leaching, runoff, or may stress the plant out to the point of making it more susceptible to disease issues.

So don’t guess. First, determine what nutrients are lacking in the soil. Contact your local extension office to see if they offer soil analysis. If the analysis indicates nutrients are present in sufficient amounts, there’s no need to apply those nutrients. It will save time and money and, most importantly, reduce the risk of nutrient runoff. A soil test costs a few bucks and tells you exactly what your lawn is short on instead of feeding it things it already has.

One thing worth knowing: fertilizers do not contain pesticides or herbicides unless otherwise indicated. Weed and feed products contain both fertilizer and weed-killing herbicides.

Herbicides: Selective vs. Non-Selective, Pre vs. Post

This is the decision that can cost you an entire lawn if you get it wrong. Two questions matter.

First, what does it kill? Herbicides used on lawns are generally selective, targeting and killing specific weeds. Others are non-selective and kill all vegetation, including your entire lawn if you choose the wrong product. Glyphosate is the common non-selective — total kill, anything green. Selective products like 2,4-D and mesotrione target weeds while leaving turf alone.

Second, when does it work? Pre-emergent herbicides kill weed seedlings as they emerge, so it should be put down before seeds germinate. Post-emergent herbicides target weeds that are already growing and requires the product to be in contact with the weed to be effective.

Timing is everything here, and in Montana the calendar lies to you — soil temperature is what counts. When to apply a pre-emergent herbicide depends on soil temperature — it should be in the 50–55 degree range. In cooler climates, spring and fall are the best time of year to apply a pre-emergent herbicide. A reapplication in spring will help the number of summer weeds. Fall application targets winter annual weeds that germinate in the fall.

A couple of weed killers worth knowing by name, both for cool-season grasses common to Montana lawns:

Product	Active Ingredients	What It Does	Temp Window	Notes
Scotts Turf Builder Triple Action	Pendimethalin, 2,4-D, dicamba	Kills existing weeds, prevents crabgrass up to 4 months, feeds	60–80°F	No more than twice a year, 2 months apart
Roundup For Lawns Crabgrass Destroyer	Topramezone	Kills crabgrass and listed grassy weeds, spares the lawn	45–90°F	Don’t seed listed turfgrasses for 28 days after

On the Triple Action: it’s for use on Kentucky bluegrass, perennial ryegrass, tall fescue, fine fescue, bermudagrass, centipedegrass, and bahiagrass. Do not use on St. Augustinegrass (including floratam), dichondra, lippia, carpetgrass, or bentgrass lawns. Also, keep it away from flowers, shrubs, fruits, and vegetables. The first three of those grasses are exactly what’s growing in most Montana yards. Bentgrass is the one to watch — it’s on the do-not list.

The Crabgrass Destroyer gives you a built-in signal. It turns crabgrass and other grassy weeds white 4–7 days after application — a whitening indicator that shows where it’s working, and it won’t harm the lawn when used as directed. Apply when daytime temperatures are between 45° and 90°F.

If it’s just a few dandelions, skip the chemicals entirely. If there are just a few weeds, consider pulling them by hand rather than applying an herbicide. A moderate number of weeds may require spot treatment with a pre-mixed, post-emergent herbicide. Lawns with an excessive number of weeds may call for a complete application.

Insecticides and Combination Products

Bifenthrin is the workhorse active ingredient in granular lawn insect control. It shows up in two common products, and knowing the difference keeps you from buying the wrong one for the season.

Ortho BugClear is the straight insecticide. It provides up to 3 months of residual control against spiders, ticks, and beetles and up to 6 months against ants. For best results apply with a Scotts spreader when you first notice insect activity or damage, then water in; treats up to 33,000 sq. ft. A 20-pound bag covers that whole 33,000 square feet. The fast-acting granules start to work in minutes (except against fire ants) and kill by contact. They work above and below the ground.

Scotts SummerGuard pulls double duty — fertilizer plus bug control. Its analysis is 20-0-8 NPK with bifenthrin as the active ingredient. It’s meant for the summer months between June and August, feeds your lawn for up to 8 weeks, and for renewed signs of insect activity a repeat application can be made but no sooner than 2 weeks after the first.

Now the part that trips people up: don’t double-treat. If you’re already running a weed-and-feed, you’ve already applied herbicide. Weed and feed products are a combination of fertilizer and herbicides. Don’t apply additional herbicides to your lawn if you’ve already applied a weed and feed product. Same logic with the 2-in-1 bug products — they’re feeding and killing at once, so you don’t stack another product on top.

And before you reach for any insecticide, a dose of reality: use a pesticide that is specifically designed to control your pest. The insect should be listed on the label. Approximately 90% of the insects on your lawn and garden are not harmful.

How You Put It Down

The application method matters as much as the product. Over 75 percent of all pesticide applications are made as liquid sprays. Granular products run through a dry spreader instead.

For most homeowners and small-acreage owners, the low-pressure sprayer is the versatile pick. Low-pressure sprayers (10 to 200 psi) are the most common and versatile power sprayer used in landscape application. They’re used to apply chemicals to turf or trees, suitable for all sprayable pesticide formulations, and can also be easily adapted for liquid fertilizer applications. When you need to reach up high or punch through thick growth, you step up. High-pressure hydraulic sprayers generate pressures over 200 psi and are used when a treatment must penetrate dense foliage or reach the tops of tall trees.

For spot work around trees and shrubs where you can’t afford drift, there’s a smarter tool. Wick applicators deliver post-emergent herbicides — the herbicide is gravity fed from a reservoir to a sponge or rope wick, which is wiped on the weed leaving a thin film. They provide an excellent method for applying non-selective herbicides around or under trees and shrubs, where drift to the nontarget plant may be harmful.

Whatever you spread dry needs to be watered in. With the SummerGuard, for example, immediately after application, water your lawn thoroughly, but not to the point of runoff.

Handling, Storage, and Keeping It Out of the Water

These are toxic products under federal regulation. In the U.S., pesticides are regulated by the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). Read the label every time — it’s not a suggestion.

The golden rule is restraint. Only apply the lawncare products that are necessary to address the problem at the lowest effective rate possible. Applying an excess of chemicals can have harmful effects on humans, pets, the soil’s ecosystem, beneficial insects, wildlife, aquatic creatures and the environment, particularly waterways. And people overdo it badly — in their zeal to control the problem, many gardeners use pesticides at over 20 times the rate that farmers do.

Runoff into Montana’s lakes, rivers, and streams is a real concern, and it’s mostly avoidable. Applying the proper amount is important, as excess nutrients can contribute to runoff and contaminate groundwater, streams, rivers and lakes. In lakes and ponds, excess nitrogen and phosphorus from runoff can promote overwhelming weed growth and cause algae bloom, which can kill aquatic plants and creatures. So do not apply fertilizer just before or during rainstorms, and do not apply fertilizers or pesticides in streamside buffers of water bodies.

Storage is straightforward. Store in a secure, well-ventilated area, such as a lockable shed. Keep them away from food, animal feed, and household items. The storage area should be cool and dry, kept out of direct sunlight, with containers tightly sealed and clearly labelled. Never use containers labelled as food or drink to store hazardous chemicals.

Disposal is not a down-the-drain situation. Never pour them down drains or storm sewers. Contact your local hazardous waste management authority to find out about hazardous consumer waste collection programs in your area. Most municipalities will have hazardous waste drop-off sites.

Frequently Asked Questions

Should I test my soil before fertilizing? Yes. Testing first tells you what your lawn actually lacks instead of guessing. Contact your local extension office to see if they offer soil analysis. If the analysis indicates nutrients are present in sufficient amounts, there’s no need to apply those nutrients. It will save time and money and reduce the risk of nutrient runoff.

What’s the difference between selective and non-selective weed killer? Selective herbicides target specific weeds while leaving turf alone. Non-selective products kill all vegetation, including your entire lawn if you choose the wrong product. Glyphosate is the common non-selective; products with 2,4-D or mesotrione are selective for use in lawns.

When do I apply a pre-emergent in a cool climate? Watch soil temperature, not the calendar. When to apply a pre-emergent depends on soil temperature — it should be in the 50–55 degree range. In cooler climates, spring and fall are the best times of year to apply a pre-emergent herbicide.

Can I use a weed-and-feed and a separate weed killer in the same season? No. Weed and feed products are a combination of fertilizer and herbicides. Don’t apply additional herbicides to your lawn if you’ve already applied a weed and feed product.

Is Scotts Triple Action safe for the grasses in my Montana lawn? For the common cool-season types, yes. It’s for use on Kentucky bluegrass, perennial ryegrass, tall fescue, and fine fescue. Do not use it on St. Augustinegrass, dichondra, lippia, carpetgrass, or bentgrass lawns, and keep it away from flowers, shrubs, fruits, and vegetables.

How much area does a bag of granular insect control cover? With Ortho BugClear, each 20-lb. bag treats up to 33,000 sq. ft. Apply with a spreader and water in afterward.

How long does granular insect control last? With BugClear, you get a long-lasting bug barrier for up to 6-months of ant control and 3-months of residual protection against spiders, ticks, beetles, and other listed insects.

What’s the most important rule for protecting waterways? Use the least you can and time it right. Do not apply fertilizer just before or during rainstorms. In lakes and ponds, excess nitrogen and phosphorus from runoff can promote overwhelming weed growth and cause algae bloom, which can kill aquatic plants and creatures.