DEAR GARDEN COACH: Oxalis and thistles have taken over my yard. Please tell me how to eradicate them for good. The overabundance of them is overwhelming me.
Tina Morrill, San Jose
DEAR TINA: Oxalis is certainly one of the problematic weeds because not only is it prolific, it has the capability of spreading even more as you weed it from your garden.
This is because just one bulb that sprouts in early spring has the energy to produce hundreds of babies within the area where it is growing, and each time you one up, a tiny bulblet is dropping back into the soil.
I’ve had success in removing oxalis by sheet mulching. To do this, remove the top green portion of the plants by either cutting back or using a weed eater. Place cardboard over the area where you removed the oxalis and top it with a thick layer of mulch — not decorative bark.
This will block light from plant, which means it cannot photosynthesize and will eventually die.
You should consider mulching a larger area than just where the patch is growing because, as I mentioned, young babies can sprout in areas far from the mother plant.
From your photo, it looks your oxalis patch is growing in and around other plants, which means it has made its home among their root system. While this might be hard to eradicate, I would still try sheet mulching the areas that are open, and then you will have to be diligent about removing the ones coming up among the other plants.
It also looks like from another photo that the milk thistle growing in your yard is coming up in a well mulched area. You should be able to pull it out easily.
If you compost, adding spring weeds to your pile is a great source of for nitrogen. Just remember that you do not want to compost anything that has already gone to seed.
Because thistles produce hundreds of floating seeds even if you have mulched you still have plants popping up each year because the seeds can travel to your yard from somewhere else. Mulching in the fall will help reduce weed crops as it blocks light and seeds cannot germinate.
I am not a proponent of chemical weed killers, but if that is the direction you want to pursue I suggest looking in your nursery or hardware store for the least toxic products.
When shopping, look for blue labels bearing a graphic of the world. These are products found to be less-toxic alternatives by a Bay Area organization called Our Water-Our World, which is working to raise awareness of pesticide use and water quality.
DEAR GARDEN COACH: What winter plants will work to feed hummingbirds?
Sandy. Houskas, Bay Area
DEAR SANDY: Hummingbirds love to feed on tubular and urn-like flowers, such as our native manzanitas, and nonnatives from Australia such as Correa. There are many species of manzanita (Arctostphylos) that fit any landscape, and some begin booming as early as December.
Other early blooming natives include gooseberry (Ribes speciosum) and chaparral currant (Ribes malvaceum).
Non-native early bloomers that compliment our Mediterranean gardens include strawberry tree (Arbutus unedo), Australian native brush (Callistemon).
Australian fuchsia (Correa alba and Correa pulchella) are some of the many Correas that bloom from late fall through spring.
