Why You Shouldn’t Grow an Avocado From a Pit

Consider this a brief public service announcement for readers in the tragically narrow avocado growing zone by way of a short review of basic plant biology.

I see a lot of grow-an-avocado-from-a-pit tutorials on the interwebs. It’s a great project for both kids and adults. If you’d like an avocado houseplant, by all means grow one from a pit. If, however, you live somewhere where avocados grow outside (USDA zones 8 through 11) and intend to plant your seedling outside, you should buy a tree from a nursery. Why? Bees love to pollinate avocado flowers. If you plant an avocado seed you’ll get some weird cross between the many different avocado varieties. Odds are it won’t taste good and who wants to water a tree for nine years only to get a bushel of foul avocados?

So to review: if you’d like a houseplant go ahead and plant that pit. If you’d like to keep your hipsters supplied with avocado toast buy a tree from a nursery or learn the art of avocado seedling grafting.

What Tree Should I Plant? Cal Poly’s SelecTree Has the Answer

Screen Shot 2017-07-28 at 8.19.02 AMTree knowledge is not one of my stronger skills. Thankfully Cal Poly San Luis Obispo has us tree ignorant Californians covered with an extensive, searchable tree database called SelecTree that will help you find the right tree for your yard.

Or, let’s say, you’re bored with hours spent adding movies to your Netlix queue that you never plan to watch (one of my vices). How about searching for oddball trees instead? What about a California native tree with favorable fire resistance, low root damage potential that produces edible fruit? The database came up with two options, the hollyleaf cherry (Prunus ilicifolia) and the saguaro cactus (Carnegiea gigantea).

Let me also put in a plug for our favorite tree, the Fuerte avocado (Persea americana ‘Fuerte’).

How to kill your palm tree

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Erik and I have been enjoying Dr. Jerry Turney’s Tree Identification classes at the Los Angeles Arborteum. Talk about high tree geekery! The last one was all about palms, and though I know that most of our readers probably don’t live in palm-friendly climates, I’m putting this out there for those of you who do, and for all you random Googlers.

My take away from the talk is that most of the horticulture problems involving palms rise from poor practice and bad information. If a palm gets enough water, doesn’t freeze, and doesn’t get hacked up by us in misguided attempts to prune them, they are stately, beautiful, easy care trees.

So these are 4 good ways to try to kill your tree:

  1. Never Water It.  Palm trees grow in the desert, yes, but they are oasis plants. They grow by open water, or above underground water. They are tough, but tough is not the same as invincible, and they don’t show stress as clearly as other trees do, so you may not know that it is thirsty until it is too late. If it gets no water, one day your palm may just droop over, like a spent flower, and that is that. As the drought in Southern California continues, I’m beginning to worry about our iconic street palms. We tend to give them no thought whatsoever, but it may be time to start watering them if we want to keep them.
  2. Over Prune. If you imagine a clock face overlaid on the crown of a palm, never cut above 9 and 3 o’clock. And never, ever, opt for the heinous and misguided extreme pruning called the pineapple or hurricane or candle style cut, which leaves just a few fronds poking out at the top. Pruning a palm this way will only stress the palm and stands a good chance of killing it. Here’s a quick photo reference.
  3. Prune your palm with dirty tools. Diseases are carried on chainsaws and the like. Poor pruning hygiene has infected the stately 100 year old Canary Island Date palms in our local Elysian Park with deadly Fusarium wilt. Simple carelessness destroyed this beloved local landmark.
  4. Climb the palm with spikes. Those spikes leave holes which do not heal. They become portals for various sorts of fungal infections. These infections can be as dangerous to you as the plant, because if the crown rots from the middle, you may not notice it is even sick until the entire crown just falls off and plummeting down, all two tons of it. Falling palm crowns smash cars and kill people.

All in all, most of the problems palms suffer come from us pruning them. The simple solution is to leave them alone. Don’t prune it if you don’t have to. Don’t be fetishistic about tidyiness. Let the palm be its natural self. It knows how to grow, it knows where it wants its fronds and boots– after all, palms are much, much, much older than us as a species. They know what they’re doing. You’ll save money and the palm will thank you if you leave it alone. If you do prune your palm, hire a company that knows what they’re doing, or research the topic well before doing it yourself.

One final fascinating fact: you can read the history of a palm in its trunk.  When it undergoes stress from extreme drought or bad pruning, the trunk contracts. If you see a trunk which has pinched areas, you know that something bad happened at that time.

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Attractive Ornamental Flowering Trees

As I mentioned yesterday, I attended a class a tree identification class at the Arboretum taught by LA County plant pathologist Dr. Jerrold Turney. During the course of the lecture Dr. Turney recommended a number of striking, flowering ornamental trees. I thought I’d list a few of those remarkable trees in case you’re considering planting one. While this list is Southern California-centric, many of these trees can be grown in other climates. All images are courtesy of Wikimedia.

800px-magnolia_stellata_in_the_jardin_de_plantes_de_paris_001Magnolia stellata (Star Magnolia)
Small trees go with small houses like gin goes with tonic water. Small trees are also easy to maintain and don’t break the bank when it comes time to call an arborist. This tree is from Japan and will grow all over North America and Europe.

754px-cornus_florida_02_by_line1Cornus florida (flowering dogwood)
One catch with this pretty tree is that it’s susceptible to anthracnose.

800px-ipe%cc%82_roxo_ype-tabebuia_impetiginosa_cemiterio_sa%cc%83o_paulo_brazilTabebuia impetiginosa (pink trumpet tree)
A tough and beautiful tree that’s great for urban locations.

tabebuia-chrysotricha

Tabebuia chrysotricha
Of all the trees Dr. Turney showed, I think this one was my favorite. The yellow flowers really pop out against a blue sky.

848px-illawarra_flame_tree_brachychiton_acerifolius

Brachychiton acerifolius (Australian Flame Tree)
Speaking of popping out, red flowers are also really dramatic.

chionanthus_retusus_-_chinese_fringetree_-_3Chionanthus retusus
Another good urban tree.

To these suggestions I’d add one of my own that also produces a tasty fruit:

redbaronRed Baron Peach
Plant one of these as a bare root tree this spring and you’ll have an attractive small tree and peaches!

Thanks to Dr. Turney for a great lecture. If you’d like to attend the other three parts of his tree identification class you can sign up here.

Trees Susceptible to the Polyphagous Shot Hole Borer

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A beetle introduced beetle, the Polyphagous shot hole borer (PSHB), is causing the loss of many trees in Southern California. Kelly has blogged about this bug before but it’s worth repeating. It’s on my mind since attending a lecture this weekend by LA County plant pathologist Dr. Jerrold Turney.

I’ve learned, as a gardener, that there are certain plants in every bio-region that simply aren’t worth planting due to pest pressures. When it comes to trees it can be frustrating, expensive and downright dangerous to have a tree attacked by an incurable infection or pest. PSHB attacks hundreds of different tree species but is hosted on a more limited number. The list of PSHB host trees is growing as scientists study the problem. When Kelly blogged about the problem in 2015 the list of known host trees was 37. The list is now at 44. Here’s that list, via UC Riverside’s Eskalen Lab:

1. Box elder (Acer negundo)*
2. Big leaf maple (Acer macrophyllum)*
3. Evergreen Maple (Acer paxii)
4. Trident maple (Acer buergerianum)
5. Japanese maple (Acer palmatum)
6. Castorbean (Ricinus communis)
7. California Sycamore (Platanus racemosa)*
8. Mexican sycamore (Platanus mexicana)
9. Red Willow (Salix laevigata)*
10. Avocado (Persea americana)
11. Mimosa (Albizia julibrissin)
12. English Oak (Quercus robur)
13. Coast live oak (Quercus agrifolia)*
14. London plane (Platanus x acerifolia)
15.Cottonwood (Populus fremontii)*
16. Black cottonwood (Populus trichocarpa)*
17. White Alder (Alnus rhombifolia)*
18.Titoki (Alectryon excelsus)
19. Engelmann Oak (Quercus engelmannii)*
20. Cork Oak (Quercus suber)
21. Valley oak (Quercus lobata)*
22. Coral tree (Erythrina corallodendon)
23. Blue palo verde (Parkinsonia floridum)*
24. Palo verde (Parkinsonia aculeata)*
25. Moreton Bay Chestnut (Castanospermum australe)
26. Brea (Cercidium sonorae)
27. Mesquite (Prosopis articulata)*
28. Weeping willow (Salix babylonica)
29. Chinese holly (Ilex cornuta)
30. Camelia (Camellia semiserrata)
31. Acacia (Acacia spp.)
32. Liquidambar (Liquidambar styraciflua)
33. Red Flowering Gum (Eucalyptus ficifolia)
34. Japanese wisteria (Wisteria floribunda)
35. Goodding’s black willow (Salix gooddingii)*
36. Tree of heaven (Ailanthus altissima)
37. Kurrajong (Brachychiton populneus)
38. Black mission fig (Ficus carica)
39. Japanese beech (Fagus crenata)
40. Dense logwood (Xylosma congestum)
41. Mule Fat (Baccharis salicifolia)*
42. Carrotwood (Cupaniopsis anacardioides)
43. California buckeye (Aesculus californica)*
44. Canyon Live oak (Quercus chrysolepis)*

If you have any of these trees here are UC Davis’ shot hole borer management suggestions:

Protect your trees and local habitat from a variety of pest species by avoiding moving infected wood around – use firewood locally.

PSHB has been found to attack healthy trees, but as always a good defense against disease is to keep trees in optimal health. Healthy trees are also more likely to recover more quickly from an attack. Choose trees that are appropriate for the site and don’t require a lot of additional water. Provide appropriate soils and access for roots to grow and expand. Avoid excessive pruning, over- or under-watering, and planting inappropriate companion plants within the dripline. If trees are infected, systemic insecticides generally are poor for treating ambrosia beetles. Prophylactic spraying of the bark could be used to protect uninfected trees in some situations. Sterilize pruning tools between uses to avoid spreading the fungus. This handout can guide you through deciding when to remove an infested tree, and how to handle the wood waste.

Chipping and solarizing/tarping infested wood can help to limit the spread of the beetle/fungus complex. Wood should be chipped to pieces smaller than 1″.

Misguided water conservation efforts have, in my opinion, contributed to the problem by stressing our landscape trees. You should keep your trees appropriately watered. And it appears that with many of these trees, including avocados, prophylactic spraying with a pyrethroid-based pesticide every three to four months will be necessary.

Dr. Turney is doing three more tree identification lectures at the LA Arboretum. More information here.