Garden questions - Davis Wiki

Tomato 'Juliet' is prolific
This page has been created as a question and answer page for anyone with garden and landscape questions. Don Shor will check this page periodically and answer general questions about gardening that anyone may have. Comments from here may also become part to the "Davis Garden Show" radio program hosted by Don Shor and Lois Richter on KDRT. Other plant experts and gardeners should feel free to contribute! (Please sign your comments.)
Don't forget to check out the resource links at the Gardening page.

Mystery plants to ID
What's this vine? (at Arb)

Ask your garden questions here!

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2010-03-31 19:46:28 No questions yet, but I love this page already. —TomGarberson

2010-04-02 12:28:44 Just to answer the most common question we're getting right now: It is TOO COLD to plant tomatoes, peppers, and eggplant in the ground! Plant tomatoes when the soil temperature is minimum 60F, which is usually when the night temperature is consistently above 50F. Plant peppers and eggplants when the soil temperature is consistently 70F, which is usually when the night temperature is consistently above 55F. For updates on soil and night temperatures, check http://ipm.ucdavis.edu/calludt.cgi/WXSTATIONDATA?MAP=&STN=DAVIS.A —DonShor

2010-04-02 12:41:01 I thought I cut my roses quite a bit in January, but they are already grown back to where they were! Is it too soon to cut them again? And how much can I cut them without damaging the bush? —CovertProfessor

You can do some pruning for size control as you trim the spent blossoms. You are about to get the first big flush of bloom, and after those fade you can cut each stem back a foot or so. But varieties differ by size, so if you want shorter rose bushes you can look for varieties that stay more compact. Floribunda roses in general get about 3 - 4', whereas Hybrid Tea and Grandiflora roses can reach 5' or more. —DonShor

Thank you, that's helpful. I will wait until after the bloom to trim. Unfortunately, I don't know what varieties I have — they are whatever the previous owner planted! —cp

2010-04-02 13:05:48 When building a set of retaining wall for a raised garden (typical small square plot with a lowered cross walk), are there any materials to avoid using for the walls? I'm concerned about chemicals that might leach into the soil from treated wood or a solid capped concrete block wall might retain too much water at the edges. Or does it not really matter? —JabberWokky

Treated wood is controversial. The general advice is to avoid CCA lumber, and look for ACQ lumber or recycled wood/composite materials. Concrete block materials work well, and it is actually useful for the block wall to retain water. One factor with raised beds is they tend to need water much more often than ground-level beds, especially if they are filled with imported soil that drains quickly. Note: when you fill the raised planter, it's best to mix the imported soil with the underlying soil. Otherwise water rushes through the nice, fast-draining soil, then hits our clay loam soil below and creates a saturated layer. —Don

2010-04-04 23:02:59 Looking for a ground-covering plant that doesn't need a lot of sunlight. My parents are in the Bay Area, in one of the valleys in the East Bay. There's several different types of taller trees, and a lot of shade between those and the house, so a lot of smaller plants don't do so well. Moss unfortunately does very well. Most of the soil isn't that great, high in clay. I've seen plants that look generically shiny and are very leafy like ivy, that spread out to cover all the ground. Any recommendations? —EdWins

Ivy itself is invasive, but Vinca minor is a good substitute (the closely related Vinca major is invasive; avoid it). Pachysandra terminalis is a popular ground cover for shade elsewhere from Davis; it doesn’t like our water here, but is a fine, tough ground cover for the Bay Area. A good native ground covering shrub is Ribes viburnifolium; hummingbirds and songbirds love it, but it may be taller than you want. A great ground cover for deep shade is Mondo grass. It can grow in very low light. It is very slow-growing, so the plants are usually spaced 6 - 8" apart. —Don

2010-04-05 08:10:57 I compost my chicken manure with pine shavings from their coop. I have been told pine shavings are very acidic, I have also been told Davis soil is alkaline. Do you think those pine shavings will create too much acidity? —DagonJones

Davis soil usually tests neutral to slightly alkaline, and the water is alkaline (pH close to 8.0). Chicken manure with pine shavings is a great additive here to counteract the pH of the water. There is no risk of over-acidulating the soil here! —Don

2010-04-28 14:25:00 I live in Oakland, and just started listening to your radio show via podcast, and want to thank you for all the good info! Thanks to you, my tomatoes aren't in the ground yet :) I have inherited a gardening problem that I want to ask you about: a passionflower vine in a neighbor's yard, planted long before I came to the neighborhood. The neighbors do minimal yard maintenance, and it has taken over their yard, their citrus tree, and 3 other yards including mine. It has well established roots and runners under deep concrete, over fences, and basically everywhere. I am a beginning gardener, and the majority of the time I spend in my garden is devoted to taming this behemoth so it doesn't cover and kill all my plants. I don't consider this very fun or rewarding, and somehow, I suspect that I'd really love gardening if I had time to do things other than ripping out vines. I read somewhere that the only way to control passion flower vine is have a good freeze, but I don't expect that anytime soon in Oakland. Is there any way to get rid of this passionate pest? —siren202020

So I don't know how to control it necessarily, but, even if you decide to take it out, take into consideration that it has some high medicinal value and at the very least dry and save some or make a tincture out of it. Don't completely throw it out without reaping some benefits. —sonyacollier 2010-04-30 16:12:14
Thanks for the suggestion, sonyacollier. Oftentimes, living with a vigorous plant and confining it to an acceptable area is the best solution. Passiflora vines root from branches on the ground, but the way they mostly become a nuisance is by sprouting suckers from the root systems — which spread far from the main plant. Other than cutting and treating the shoots chemically (which could damage the main plant), the best way to manage woody nuisance plants is by smothering them with landscape fabric and mulch. The fabric is fastened securely to the soil with anchor pins, which are available from the drip irrigation section of your favorite garden supply or hardware store, and then you put any kind of attractive bark mulch on top. New plants can be put in by cutting an X in the fabric, folding back the material and planting. Keep the fabric and bark away from the trunk of the new plant so you don't trap moisture against the bark. Spreading shrubs that will grow out over the fabric and bark will be effective; examples include Euonymus fortunei, prostrate forms of Ceanothus, or Rosmarinus officinalis 'Irene'. —DS

2010-04-30 22:42:41 We also discussed this on our 4/29 broadcast on KDRT. Thanks for the question! —DonShor

2010-05-24 17:36:18 In looking for a US zone map, I was surprised to come across many sites that dismiss with distain the USDA zone guidelines as being utterly useless. While it does make sense to regard them as guidelines rather than some kind of law with engineering precision, I didn't know there was such venom directed against them (several of the sites were nurseries). Is this view common among today's gardeners, or is this a function of either the internet (where dismissing commonly held beliefs is often seen as somehow sophisticated), or nurseries (which might not want people to limit themselves in what they buy)? —JabberWokky

the USDA zones simply describe the lower temperature range plants can survive. That makes them pretty limited for predicting whether a plant will do anything other than make it through the winter. There aren't many other ways that Davis, CA, is similar to Brownsville, Texas or Fort Pierce, Florida in terms of gardening conditions. Sunset zones are much more detailed, using regional climatic differences affected by humidity, coastal breeze, etc. Davis is Zone 14, Woodland is Zone 8, much of Sacramento is Zone 9. The main difference between those zones is the range and frequency of the delta breeze. Sunset zones used to be just for the western states, but now exist for the entire continental US. —DS

USDA: http://www.usna.usda.gov/Hardzone/ushzmap.html
Sunset: http://www.sunset.com/garden/climate-zones/
There is an excellent overview of some of the problems with the USDA zones at: http://www.hardinesszonemap.com/
—DonShor

2010-05-25 21:21:30 I've got a pretty loose potting soil in my homemade inverted tomato pot, and water seeps through it pretty quick. Any general advice on various tools to simplify the watering of pots? My folks use some little plastic widgets you can stick a plastic water bottle into upside down that will regulate the water flow. I know there are also those gel things that'll soak up water and keep things moist for a bit. I'm used to watering near-daily, but it'd be nice to have a backup just in case I forget or get lazy. —TomGarberson

Here is a simple answer and here is an incredibly complicated one. (I really think the second guy should take up some other hobby — model railroads, or something.)
Your parents' device works fine for short periods. It's always best to water enough that water drains through and runs out of the pot, as we have lots of salts in our water and they accumulate in the soil if you don't flush them out. Their technique, as with the Aqua Globes (As Seen On TV!), only puts in water as it is used, so the salts don't leach out. Ok for a weekend or so, but not throughout the season.
In a pinch, just put a half-dozen ice cubes on the soil and let them melt during the day. That's a trick used at trade shows. —DS
This is a great topic. The makeup of the potting soil affects how often you'll have to water. We'll answer in more detail on the 5/27 garden show broadcast (Thursdays 12 - 1 on 95.7 FM KDRT, also available live-streaming at KDRT.org and by podcast). —DS

Ok, we finally got around to this topic today! http://kdrt.org/station/programs —DonShor

As always, thanks for all the great advice, Don! -tg

2010-08-01 19:31:58 What is the best way to start a new plant from a larger existing tree or shrub. I have some hormone (auxin I think) that is supposed to work as a root starter. I have an existing flowering maple and lavender. I think the lavender is a French variety with the long thin stalk like in the west beds in front of Bistro 33 —DagonJones

Softwood cuttings are the easiest way to root lavender and flowering maple (Abutilon). You take 3 to 4" long cuttings, preferably each with a growing shoot tip. Woodier pieces tend not to root as well. Strip off any leaves from the lower half of each cutting. Dip each in the rooting hormone (usually it's a powder; sometimes it's a liquid). Immediately push the cuttings into a mix of fast-draining, naturally sterile media; you can put several together in a small pot. A good combination is equal parts peat moss, perlite, and sand. Any combination of those will do; vermiculite is also fine if you can find it. Don't use compost or garden soil, and regular potting soil isn't great. You want fast drainage and ingredients that don't naturally support fungus or bacteria. To reduce water loss, very leafy cuttings such as the Abutilon should have each leaf cut in half. Place the pot in bright light in a window, or outside in a shaded area that is protected from wind. Keep the soil evenly moist and don't tug on the cuttings for at least 4 - 6 weeks. You should get anywhere from 25% - 100% rooted in a few weeks, at which time you can separate them into individual 4" pots in a good quality potting soil. —DS
I reviewed this question on today's Davis Garden Show broadcast, MP3 file available for download at http://davisgardenshow.com/DavisGardenShow20100805.mp3 (all shows archived at KDRT.org or by podcast thru iTunes.) —DonShor "2010-08-05"

(follow-up)
What do you mean by softwood cuttings? what part of the plant is that? by growing shoot tip do you mean the top of the plant? —DagonJones

Yep, "softwood cutting" is industry jargon for the new growth. The tender green shoots that have not yet become woody. Here are some examples of types of cuttings. —DS
Also talked about this topic on the 26 Aug 2010 show of the Davis Garden Show, MP3 file available at: http://davisgardenshow.com/DavisGardenShow20100826.mp3 —Lois Richter

2010-08-06 11:06:29 I gave up on my garden this year when I realized that all I was doing was making a glorified animal feeder. EVERY time I saw a hint of a fruit it got eaten by something that wasn't me. Squirrels? Birds? I don't know. I ate one strawberry that was terribly under-ripe just because I wanted to snag it before the animals did. What can I do to avoid this? My plants are all in pots right now but by next year I hope to have my planter box (about 6 feet square) full of dirt and plant in there instead. I know chicken wire is an option but that wouldn't protect against birds and since the plants/box are right next to a fence it would probably just trap squirrels INSIDE there with the plants. Maybe I need one of those laser thingies they have protecting expensive stuff in museums in movies. —JenniferCook

Thanks for your story. It was read on our show and used as a starting point for discussion of mammals, birds, and other things that eat our fruit and veges. Perhaps Don will write out some suggestions here later, but if you'd like to listen to that show in the meantime, you can download the MP3 file from: http://davisgardenshow.com/DavisGardenShow20100826.mp3 —Lois

2010-09-04 20:14:01 My parents have a fruit tree they bought and planted sometime last year: "Fuyu Persimmon (Jiro)" and it says "rootstock: Lotus Persimmon." They also planted a Meyer lemon tree and some other fruit tree in the same area/row. All three trees took, but the persimmon tree is growing a bit funny. It was maybe 6 feet tall when they got it and thin. It's now over 10 feet tall, but still super thin. It's got leaves and little branches almost along the whole length, but we're concerned that it's going to outgrow the wood its propped/lashed to and fall over. Is there something they should be doing differently? Some way to make it thicken/strengthen up or is that natural for a persimmon tree? It looks like it's only two to three inches thick, so I really dont think it'd support it's own weight. —EdWins

Once the tree drops its leaves, they can prune it back some. This is when they decide what the ultimate shape of the tree is going to be. If they want a tall tree with a central leader, they should prune lightly and not head it back. If they want better access to the fruit, they can prune it down to an existing lateral branch. It's ok to remove 1/3 to 1/2 of the tree to force lower branching. They do need to re-stake it. A tree that is lashed to a single pole can't move and won't develop the reaction wood that makes the trunk thicker. So they need to double-stake the tree: two lodgepole stakes 6 - 12 inches out from the trunk on the east and west sides, with the tree tied at the point of the bend. Those stakes can probably be removed next summer as the tree develops more taper and a stronger trunk. —DonShor

2010-09-23 10:10:16 Most of my spring vegetables are done for by now (still getting some late tomatoes and peppers) but I would like to know what I should plant now so I can get crops through winter. I have planted some snap peas. I have raised beds with about 8-12 inches of imported soil. —DagonJones

Here is a list of what we plant in the fall, and here is a chart showing the season. Some are planted from seed, others from young starts.

Right now we plant:
Cole crops: broccoli, cabbage, cauliflower, collards.
Onion family (onion starts arrive in November)
Root crops: beets, carrots, radishes, turnips.
Lettuce and greens, including chard, kale, spinach.
Peas: shelling, snap, and stir-fry.
Potatoes
—DonShor

2011-02-10 12:29:29 I recently moved into a house with a nice sunny garden spot... filled with bermuda grass. Is there any way for me to get rid of the grass in time for a summer garden? There is one small raised bed which I can keep pretty well weeded but I also want to utilize the ground space which is hopelessly full of bermuda. I don't think I have the time or money to build more raised beds. What can I do? Thanks! —ShannonSeil

Hi Shannon,
Bermudagrass can be dug out, but every little piece of rhizome that you leave behind will sprout again. You can smother it with black plastic, landscape fabric, and/or thick mulch, and then dig or cut it as it sprouts along the edges. Organic gardeners usually dig the bed thoroughly, adding whatever organic material they are using (manure, compost, etc.). Install whatever watering system you are using: drip irrigation tubing with emitters, soaker hoses, etc. Then cover the bed with landscape fabric, which you secure very thoroughly to the edges of the bed with anchor pins or blocks. Cut slits into the fabric to plant your seedlings, placing them close to the water source (drip emitter or soaker).
Bermudagrass cannot grow without sunlight, so it will only sprout along the edges — and possibly where you have cut in to plant your tomato plant. Keep covering any foliage that you see, or keep cutting it, so it doesn't overtake your vegetable plants. Some people spray the tops with organic herbicides derived from soap or vinegar, but those only kill back the foliage.
Systemic herbicides such as glyphosate (RoundUp) work by killing the whole root system of the bermudagrass. They are labelled for careful use around edible plants, but they are most definitely not organic. —DonShor

2011-02-15 10:42:41 So I brought my Hybiscus plants inside last fall — and some have been blooming nicely all winter. What temperatures do I look for before I put these back out in the yard? (No special place, just outside in general.) THANKS! —LoisRichter

2011-08-08 16:04:24 Has anybody here had any luck growing rhubarb in Davis? —MeggoWaffle

Yes. Rhubarb likes good drainage, so plant it in a raised bed, or at least crowned up above the surrounding grade. Water it infrequently: it's better near your orchard than your vegetable garden. Plants tend to last a few years. They are available in the bareroot season; i.e., January - February. Sometimes they are available in the spring in containers. —DonShor

Thanks Don. I have read that you can't even really harvest rhubarb for more than a year after it's planted... and I'm a renter so I'm not even sure if I'll be in the same place for more than a year. Do you think planting it in a large pot or planter so we could take it with us would work? -Megan

2011-08-08 16:27:58 What tree has been leaving a very sticky film on our patio each night? We are in a rental home in east Davis (near Slide Hill Park). Thanks! —Chamoudah

It could be a Chinese hackberry, Celtis sinensis, which commonly leave a sticky honey dew residue from aphids that feed on the tree. Here is a link to a picture via google. Also, here is a link to what you can do about it. — Christy
An article I wrote when the Asian Woolly hackberry aphid showed up in 2002 has some photos of the pest, and some links. The IPM article Christy linked is very thorough. Most people just live with it; some use systemic pesticides. The substance they excrete is basically sugar, so it does wash off. —DonShor

2012-03-29 08:53:38 I have some oregano in a raised bed with commercial soil in my backyard. The oregano is growing very well but it is about 2-3 years old now and it seems to have lost most of its flavor and scent. Im not sure what is going on here is this common for oregano? I don't cook with it any more because it is so bland, at this point it is just decorative foliage. —DagonJones

Hi, Dagon, Lois Richter and I talked about your question on the March 29 2012 Davis Garden Show (http://kdrt.org/node/8966). Most common answers we find on this are that it makes less of the pungent oil when it flowers or has flowered, and that flavor and aroma are likely intensified during hot, dry weather. Also, reduced nutrition and minimal watering probably encourage maximum flavor. Last resort: plant another one! —DonShor

2012-04-17 23:02:40 April 17,2012

Hi,

I am a long-time listener of your podcast. I love it. Thank you! It has given me many pleasant, peaceful hours.

I live in San Mateo, CA (near San Francisco) and this time of year there are many beautiful flowering trees (white flowers, pink flowers). I THINK they are either plums or cherries, but am not sure. Here's my question:

How do you tell a plum tree from a cherry tree?

Any insight you have will be MUCH appreciated. (I have tried looking is several tree-identification books and online, but was unsuccessful in finding how to distinguish a flowering cherry tree from a flowering plum.)

Thanks so much!!!!!!!!!!

Nancy Pope

We discussed this on a show right after you sent this question. But here is the simple thing to look for:

You will find these visible nectary glands on cherry leaves. —DonShor

2012-05-21 10:13:02 I am moving to Las Vegas at the end of the month, and I would like to keep one or two potted plants on my back patio there. What types of plants can withstand the Las Vegas climate besides cacti? —LoriOrf