· by Michael Blair, Nashville's Weed and Feed
A weed-and-feed bag promises two jobs in one pass of the spreader: fertilizer for the grass and a weed killer riding along with it. On a Middle Tennessee lawn the combination is less convenient than it sounds. The herbicide lands on every square foot, including the ground where tree and shrub roots run under the turf, and the two halves of the bag rarely want the same week of the year. Here is what three extension services say about both problems, which lawns the bag can suit, and how we split the work on a weed control program instead.
Does weed and feed harm trees?
Weed and feed can injure trees and shrubs, because their roots live under the lawn it is spread on. The University of Florida’s IFAS Extension, in Right Fertilizer, Right Place, explains that the roots of some trees and shrubs reach far past the drip line, mingle with the grass roots and take up the herbicide from the product. Oregon State University Extension says the same on its page about protecting non-target plants: root zones can extend well beyond the canopy, and where tree or shrub roots run under a lawn, products containing 2,4-D should stay out of that zone.
Neither source gives a safe distance from the trunk, and we will not invent one. What they agree on is that the drip line is not the edge of the roots. On a yard with mature shade trees and foundation shrubs, very little of the lawn is outside somebody’s root zone. Oregon State also quotes a typical label caution, which tells the user to keep the product off ground where the roots of plants they want to keep may reach, unless they can accept the damage. That line is worth finding on the back of any bag before it goes in the spreader.
Why is the timing of a weed and feed bag usually off?
The timing of a weed-and-feed bag is usually off because its weed killer and its fertilizer do their best work months apart. UF/IFAS describes these products as fertilizer combined with a pre-emergent herbicide, and notes that pre-emergents generally belong much earlier in the year than fertilizer does, so the combined product often leaves one half or both less effective. The University of Georgia Extension office in Forsyth County puts the underlying rule plainly in its article on pre-emergent timing: grass should only be fertilized while it is actively growing.
A pre-emergent has to be down before crabgrass seed sprouts, and our post on pre-emergent timing in Nashville covers how we pick that window. Fertilizer goes on when the grass can use it, which for fescue follows its own calendar, set out in when to feed a fescue lawn. When one date has to serve both, one of them is going down at the wrong time.
Can you use weed and feed on bermuda grass?
Weed and feed is the wrong product for bermuda, according to the University of Georgia Extension, and the same holds for zoysia and centipede. Its Forsyth County article calls weed-and-feed products never a good idea on these warm-season grasses, because they do not begin active growth until April or May, and by then the fertilizer applied with an early pre-emergent has already left the root zone. The weed killer arrives on time and the feed is wasted.
Tall fescue is the one lawn where the same article allows it. Fescue is a cool-season grass that needs feeding in February and March, the same window as a spring pre-emergent, so a combined product can serve both jobs there. The late-summer pre-emergent is another matter: UGA notes that it is still a little early to fertilize fescue at that point. Georgia’s calendar does not match Tennessee’s to the day, so we take these as the reasoning rather than the dates, and set the actual timing by the grass in front of us.
How we treat a lawn instead of using one bag
We handle the weeds and the feeding as two separate jobs, each on its own date. UF/IFAS recommends applying herbicides only where the problem is, rather than broadcasting them over the whole yard the way a weed-and-feed product does, and that is how we treat broadleaf weeds: spot treatment on the patches that have them, and none over the root zones of trees and beds. Fertilizer goes down on its own schedule through our fertilization service, matched to whether the lawn is fescue, bermuda or zoysia.
Whatever product goes down, the label is the rule. UGA reminds homeowners that the application rates printed on a label are legal limits, and we read labels for the root-zone caution as closely as for the rate. If you have been spreading a combined bag under trees that have started to thin, or you are not sure which grass you have, ask us to look at the lawn before the next application.
Sources
- University of Florida IFAS Extension, Gardening Solutions: Right Fertilizer, Right Place — Weed and feed combines fertilizer with pre-emergent herbicide; pre-emergents belong earlier than fertilizer, leaving one or both less effective; tree and shrub roots beyond the drip line absorb the herbicide; apply herbicides only to affected areas (a Florida source, used for the mechanism)
- Oregon State University Extension, Pesticide Safety: Non-target plants — Root zones extend beyond the canopy; avoid 2,4-D products in the root zone of trees and shrubs under a lawn; a typical label caution about desirable plants’ roots
- University of Georgia Extension, Forsyth County: Apply pre-emergent herbicide now to reduce lawn weeds — Fertilize only actively growing grass; weed and feed suits tall fescue in February and March but not the late-summer application; never a good idea on bermuda, zoysia or centipede; label rates are legal limits
FAQ
Is Weed and Feed Safe Around Trees and Shrubs? — questions
Is weed and feed safe around trees?
Not reliably. UF/IFAS Extension warns that some trees and shrubs can be hurt by weed-and-feed, because their roots reach past the drip line and take up herbicide from the lawn. Oregon State Extension advises keeping 2,4-D products out of root zones under a lawn. No source gives a safe distance, so read the label’s caution first.
Should I use weed and feed in the fall?
Not as a rule. For tall fescue, the University of Georgia Extension says the late-summer pre-emergent comes a little early for fertilizing, so a combined bag is mistimed then. For bermuda, zoysia and centipede it calls weed and feed never a good idea. We put down a fall pre-emergent and fertilizer separately, each when it fits.
When should you weed and feed your lawn?
Only on tall fescue, and only in February or March, according to the University of Georgia Extension, because that is when fescue needs feeding and a spring pre-emergent goes down. On warm-season grasses the feed arrives before the grass is growing. Even on fescue, the herbicide still reaches any tree and shrub roots under the turf.
Can you use weed and feed on zoysia grass?
The University of Georgia Extension says no: weed-and-feed products are never a good idea on zoysia, bermuda or centipede. These grasses begin active growth in April or May, after the fertilizer from an early pre-emergent application has left the root zone. Treat the weeds and feed the zoysia separately, each on its own timing.