Dear Garden Guru,

I have teeny tiny ants, millions of them, in the soil under some of my potted plants. How do I get rid of them? They are climbing up into the pots and that can't be a good thing for my flowers. Thanks.

Elizabeth in San Rafael

Hi Elizabeth,

You can get rid of your ants with the Green Light Slug and Snail (it also is effective on ants, sow bugs, and earwigs). Sprinkle some under the pots as well as the soil in the pots. This is an organic remedy based on boric acid.

Dear Garden Guru,

What is the best way to get rid of gnats? I have tried the vinegar trick, the water trick, the potato trick and none seems to work. I even tried a few different sprays. Please help.

Kelvin in San Francisco

Hi Kelvin,

You don’t say what type of gnats are bothering you. I will assume you are referring to gnats in your potted plants. The best way to get rid of them is to apply beneficial nematodes to your containers (Fungus Gnat Destroyers). The nematodes will feed on the hatched maggots and pupae in the soil thus breaking the cycle. You can attach yellow sticky traps (Gnat Stix) to trap the adults at the same time. The gnats are attracted to soils rich in organic matter (peat moss, manure, compost) and kept too wet.

Dear Garden Guru,

I see your very first question for Feb is about our dear friend, Oxalis. Maybe you can help with mine on the same subject: Is the yellow oxalis that is covering our hills (see Bernal Heights et al) and sprouting in our gardens now a non-native variety? Is it in fact from South Africa as local legend has it? And what exactly is its genus/species? I've researched (and argued about) this issue with many but cannot find a definitive answer. Thanks for any help!

Ed in San Francisco

Hi Ed,

This pretty little non native is now considered an invasive weed threat. It is indeed from South Africa and is known as Oxalis pes-caprae (Synonym O. cenua). It does not spread by seed but asexually by lateral roots and many small bulblets that are formed along it’s tap root under the soil. At least there is no evidence that it sets seed. It spread first to the Mediterranean in the 19th century and then to the Americas. It was mentioned in Bailey’s Horticultural Manual in the 1930’s after it was probably collected for use as an ornamental. There is no mention of it being in California prior to 1925. It was first noticed (or rather recorded) to be prominent in southern California orchards and vegetable fields in 1951. How did it spread? Bulblet contaminated soil on shoes, tractors, tires, tools, or innocently planted by people who dug it up to plant in their yards. It could have been spread by imported bareroot trees. In any case, it certainly has taken “root” along our coast.

Dear Garden Guru,

Every year there is more liver wort in shady areas of my 1/2 sunny garden in Noe Valley. I have just scraped a lot of it off with a trowel. I plan to amend & plant some cool vegetables there. What can I do to remove it permanently?

Heather in San Francisco

Hi Heather,

Liverwort loves moisture, loves nutrient rich soil. Amending your soil with a compost should help as the top of the soil where the liverwort lives will tend to dry out faster. Avoid using liquid fertilizers in areas where liverwort thrives. You are better off, mixing in a dry fertilizer into the soil or using a preplant fertilizer such as Sure Start and incorporating a slow release such as Osmocote at the same time. Liverwort can be killed by spraying it with vinegar. Household vinegar is a 5% concentration that will work on rootless liverwort (it is not strong enough for other weeds). We also have a vinegar based herbicide called Burn Out that has a higher 6.25% concentration. As for permanent eradication, the more you are able to scrape away and dispose of BEFORE it flowers (those odd umbrella-shaped structures), the less spores you will have to hatch at later dates.

Dear Garden Guru,

Help! That beautiful little patch of Baby Tears in my shady flowerbed has turned into a massive tidal wave of green, engulfing its less aggressive neighbors. What is the best way to keep it under control?

Sue in Dublin

Hi Sue,

Baby Tears grows best with ample water/moisture and regular exposure to fertilizers. To culturally slow down the beast, avoid feeding it and reduce the watering if the companion plants will accept this. You may have to physically remove it by scraping it off, including some of the underlying soil it has rooted into. Do not apply mulch around the baby tears as it will find this looser material easier to root into. Once you have it as far back from companion plants as you want, you can periodically spray encroaching growth with Burn Out, a vinegar based weed killer that will kill back only the foliage sprayed.

Dear Garden Guru,

I have a dwarf lemon tree on my deck and it seems to be infested with inchworms, small green inch worms. What is a safe, organic, non-toxic way to get rid of these. Are there any predators like praying mantis etc? Thanks for your help.

David in San Francisco

Hi David,

The easiest and safest way to rid yourself of the caterpillars is to spray your citrus with Bonide Caterpillar Killer, also known as B.T. Bacillus thunbergiensis is a naturally occurring bacterium that when ingested by caterpillars, causes them to stop feeding and subsequently perish. It is safe for wildlife, kids and pets. There is not a commercially available predator to control inchworms handily. Praying mantids would consume a few but they do not hatch until about May.

Dear Garden Guru,

We live in a high humidity coastal climate and have a large population of earwigs and pill bugs. We are highly against using insecticide due to harming of good insects. Are earwigs and pill bugs harmful to plants and vegetables?

David in Pacifica

Hi David,

Pillbugs, and especially earwigs can be harmful to plants. Earwigs are notorious flower petal eaters. They can quickly destroy Dahlias, daisies, and other prized flowers. They feed on tender seedlings and new transplants. Pillbugs, in small numbers are not as harmful. They feed mostly on garden detritus. In larger numbers, they will aggressively eat seedlings just as they emerge from the soil. Sunflowers, beans, and peas are most susceptible. There is a safe, organic control for these bugs, Sluggo Plus. This product contains iron phosphate, a naturally occurring mineral, and spinosad a bacteria/actinomycete The bait has to be ingested therefore, it does affect predatory beneficial insects. The iron phosphate kills slugs and snails and the spinosad works on ants, earwigs, pillbugs.

Dear Garden Guru,

Can you recommend a mosquito spray that is harmless to plants & house paint? They hang out in our potato vine at the front door.

Caryn in Marin

Hi Caryn,

We do have two options that should work well for your situation.  The first is the Bonide Mosquito Beater in a ready-to-spray bottle.  It repels mosquitoes, gnats and flies in any outdoor area including patios.  It is an all natural product so it’s safe to use on your plants and safer for you and your family than chemical alternatives.

Here’s a link to review the product online:  http://www.planetnatural.com/site/mosquito-spray.html

We also carry Cedarcide YardSafe Insect repellent in a ready-to-spray bottle. It also repels mosquitoes and other flying insect and is 100% organic.  It can be used on vegetables and any other plants you might have, plus it can be used indoors if necessary.

You can see more info here:  http://www.planetnatural.com/site/cedar-repellent.html

With both of these products I can not guarantee what they will do to house paint.  Your best bet with any product you purchase to battle the mosquitoes is to test it on a small section of painted area to see what effect it has.  They are both natural oils so I don’t believe they will cause damage, but oils can potentially make some paints run, so please do be careful and do a test.

Also, the websites that I’ve linked you to do sell these two products, but I would alert you to the fact that their shipping charges are rather high, so your best bet would be to simply visit any of our Sloat stores to get the best value.  Plus our team members can continue this discussion with you in person if you like.  If there is a particular Sloat store that you like to shop at, just let me know and I’ll be sure that they have these choices in stock for you so that you do not waste a trip.

Dear Garden Guru,

In my Noe Valley garden roses with 6 hrs sun are already covered with holes and brown & rust. I dormant sprayed and cont. to spray with 'rose defense' every 2 weeks on both sides of leaves. I have seen little green worms. Might Volke oil spray help? I am going to be away for a few weeks what shall I do to try and avoid any more damage?

Heather in San Francisco

Hi Heather,

Your rose woes are part really wet weather and possibly the varieties you are growing. Some varieties are known black spot/rust machines. I would not spray with the oil spray at this time. Many of our customers have had great success with the Bayer rose and flower drench. While not considered organic, it does control all the bugs and fungus as well as feed. If you are opposed to a non organic control, I would prune back the roses that have finished flowering and remove as many of the affected leaves from top to bottom. Give them a feeding of Sul Po Mag to improve their disease resistance. Warm weather, or at least drier weather will help your bushes “turn the corner”.