How can I help a newly sprouted seed lawn compete with faster growing clover?

Question

I have exciting new grass seedlings sprouting, some weeds appear to be gaining:

My basic questions:

1. Is it better to manually pull the oxalis, or let the grass try and compete?

2. If I pull, how much do I have to get out? Is it better to wait for the plant to grow big and easy to pull?

3. As an experiment I created a cardboard ring to protect the grass, and sprayed Glyphosate carefully. The clover turned sort of yellow but that's it. What should I expect?

4. As an experiment, I use a "natural" weed killer. This rots the leaves and stems the same day (much faster than the Glyphosate). I used "EcoLogic" a concoction of rosemary oil and sodium laureth sulfate (sodium lauryl ether sulfate ).

The seed bed was prepared by mechanically removing the turf, watering for 2-3 weeks to sprout weeds, mechanical removal, then 2 inches of fresh soil and a high quality deep rooted grass seed variety. The garden all around has clover everywhere on all sides, and has for decades.

If I dig enough, I can often get the onion like bulb at the base of each "clover":

But the basic question is if I pull the weed and it breaks above the bulb, is the bulb going to sprout again? Some start tiny and don't seem to have bulbs, is this rhizome spread?

Answer 1

First off, the "clover" in your photo is actually not clover, it's oxalis. This explains the bulb you're finding when you dig it out. You also have nasturium and, oddly, something that looks like sagittarius, which is usually associated with water, in that photo. Where did your two inches of fresh soil come from?

There are many oxalis species, and some are considered good garden plants. I'm wondering if the ones in your garden self-seeded from a long-ago garden oxalis and have now moved into the lawn. There is one that's also a common lawn weed (yellow woodsorrel), and yours could be those, too.

Because oxalis has a bulb, it is difficult to eradicate unless you manually remove every bulb in the lawn AND prevent any plants from going to seed. I have a weed with a bulb in my garden and yard (Ornithagalum, AKA Star of Bethlehem) and it has been a many-year project to remove it from the garden. After seven years, I'm not free of it yet. Don't ask about the lawn... (at least it goes dormant in early summer).

Clemson University has an excellent page on controlling oxalis (they concentrate on yellow woodsorrel, but their recommendations should be applicable to any other species in the genus). During the time you're spraying it with herbicide, you need to make sure that any of the plants in the lawn (and in your garden) do not set seed, or the seeds will almost certainly infiltrate your lawn. You'll then need to treat with both pre- and post-emergent herbicides.

Answer 2

Couple of points. First, many weeds can't cope with being regularly mown. So you might want to wait for a while to see how much of a problem there is before resorting to weedkillers, hand weeding, etc. Second, unless you're managing sports turf (where weeds are a real problem), you don't really need a weed-free lawn. In other words, it's not written in stone that a "good" lawn consists of nothing but grass, and a "bad" lawn is full of weeds. As the RHS put it:

One gardener’s weedy lawn is another's wildflower meadow. The more plants grow in your lawn, the more biodiverse it will be. If you really want to remove the plants you consider weeds, try hand weeding first and, as a last resort, selective lawn weedkillers are available to use.