Saturday, August 30, 2014

Washington windmill palm winners (and losers)

Trachycarpus fortunei
Scottish Rite Temple, October 2012

In early February, when we were in the middle of our coldest winter in a very long time, I wrote a blog post rounding up several windmill palms (Trachycarpus fortunei) that I've encountered in the city.  Most of these palms were several years old and had suffered little damage from our recent mild winters but as I wrote in February, "...our coldest winter in 20 years will surely put these palms to the test.  A general rule of thumb is that single digit temperatures are likely to cause damage, and temperatures below zero will cause massive damage and in many cases kill the palm outright (although duration of the cold is also critical).  This makes windmill palms marginal in zone 7: sooner or later, they will experience temperatures capable of killing them."

Thursday, August 28, 2014

Basil Downy Mildew: say good-bye to pesto

Basil downy mildew
Yellowing leaves: an early sign of Basil Downy Mildew

I just harvested what will probably be my last batch of basil (Ocimum basilicum), for what will probably be my last batch of pesto this year.  This is depressing for several reasons.  First, I love basil and I love pesto, and I always find the end of the basil season a bit depressing.  Second, my basil usually lasts much longer, only petering out in October once nights start turning consistently chilly.  But most of all, I'm depressed because I discovered that my basil has Basil Downy Mildew, a new disease that I've never encountered before, and that promises to be a major problem for basil growers--and lovers--in the next few years.

Basil downy mildew
Leaf discoloration from Basil Downy Mildew

One thing I love about basil is how fast it grows, and how productive even two or three plants can be.  I grow my basil in a container on my back deck, where it gets the heat and sun it loves all day long.  I never start it from seed, always buying plants from a local garden center or farmer's market, and this year started like any other.  The first sign that something was wrong came just a couple of weeks ago, when I noticed yellowing older leaves on my basil.  But it was still vigorous and growing strongly, was yielding well, and I thought maybe I had stressed it by over- or under-watering it.  Consistent watering is not my strong suit!  But the yellowing progressed, the older leaves developed brown lesions and started dropping off, and younger and younger leaves were affected.  When I harvested the basil I noticed a dark fuzzy discoloration on the leaf undersides, which I assumed was some kind of mildew.  I still wasn't terribly concerned; I've had mildew on various garden plants, and this seems to be an especially bad year for powdery mildew on several plants that are prone to mildew anyway: peonies, columbine, and Verbena bonariensis.  I've never seen mildew on basil before, but I chalked it up to the summer being a bit cooler than usual, because basil certainly loves heat.

Basil downy mildew
Leaves infected with Basil Downy Mildew, bottom (left) and top (right)

But the disease progressed rapidly so I did some Googling and that's when I started to get a bit alarmed.  I sent photos to Margaret McGrath, a plant disease researcher at Cornell University, who confirmed that my plants had Basil Downy Mildew (BDM).  BDM is a new disease, reported in Europe in 2001 and found in the United States for the first time in Florida in 2007 but already reported from all over the country, even Hawaii.  The disease spreads quickly and easily, progresses rapidly, and can wipe out a grower's entire crop of basil in a matter of weeks.  Even in its early stages the plant's foliage is disfigured and ruined for commercial use.  I'm lucky this is the first time I've encountered it, but this isn't likely to be the last.  No basil cultivars are (yet) known to be resistant, so I suppose that gives the plant breeders one more thing to keep them busy!

Basil Downy Mildew
Underside of leaf infected with Basil Downy Mildew

Basil downy mildew can be controlled with fungicides, but I don't use pesticides of any kind in my garden so for now I'm at a bit of a loss and don't have any tips for control.  The best advice is probably to monitor plants closely and immediately remove and destroy any that show even a hint of disease.  The good news is that the mildew isn't toxic to humans, although it can and will kill your basil.  More good news is that the disease probably (probably) won't survive cold winters; but it can spread by infected seeds so if you have BDM-free plants it might be wise to save your own seeds and grow your own!

Please share this post to help get the word out about this destructive new disease!  Dr. McGrath and her colleagues are gathering reports of Basil Downy Mildew so if you have it, you can report it here: Basil Downy Mildew Monitoring Program (this link also has information on submitting samples).  Has anybody else in the Washington, DC region encountered this disease?

For more info:

Expect and prepare for downy mildew in basil (Margaret Tuttle McGrath, Cornell University)
Downy mildew on basil (photos, Cornell University)
Basil Downy Mildew and the Ornamental Greenhouse (A.R. Chase, GPN)
Fungus threatens basil plants for this year and beyond (Adrian Higgins, Washington Post)
Downy mildew on basil (Nancy F. Gregory, University of Delaware)
Basil downy mildew (University of Maryland Extension)

Saturday, August 23, 2014

What's missing from this picture? (Hint: palms)

Garden, late August
Garden, late August 2014

What's missing from this picture?  Those of you who have been following my blog since last year (or who read the post title) probably have a good idea.  But this photo from the same time last year really brings it home:

Wednesday, August 20, 2014

Raleigh, part 2: Plant Delights Nursery and JC Raulston Arboretum

Crinum
Crinum and Yucca

[Part 1 here: Southeastern Palm Society summer meeting.]

I spent a pleasant and only moderately wet morning taking photos at Plant Delights Nursery and chatting with Tony Avent.  In retrospect (especially considering the afternoon rain that made photography nearly impossible later in the day) I probably spent too much time with the begonias, but that's one of my current interests and it's what I wanted to see.  Tony is very interested in begonias (although I've yet to find a plant group he's not interested in) and has acquired quite a collection of species and hybrids at the nursery to test for hardiness and commercial potential.  We compared notes at length on hardy begonias, not just B. grandis but several other species and hybrids that are proving to be fairly hardy, as well as my own efforts to breed hardy begonia hybrids.

Sunday, August 17, 2014

What to do with a dead tree

Garden (cropped)
Garden, this time last year (note fig at upper right)

What do you do with a dead fig tree?  Okay, it isn't actually dead, although for quite a while I feared it was; it took its sweet time but it's finally putting out strong new growth from the base.  Who knows, I might even get some figs next year!  But in the meantime, what to do with the dead trunk and branches?  I suppose I could have cut it to the ground, but I kept hoping it would finally leaf out, right up until that time of year when I pretty much stop working in the garden because it's too hot, too humid, and too buggy.  (At least that's my excuse for what is probably just plain laziness.)

Friday, August 15, 2014

Garden Bloggers Bloom Day: August 2014

Okay, enough with the long blog posts for now!  It's time for a quick-and-dirty blog post with pretty pictures and not much else.  These are some of the plants I had blooming in my garden today.  For more information about any of them, feel fee to post questions in the comments section!  For many more photos, click here.  For more Garden Bloggers Bloom Day posts from all around the blogosphere, visit Carol at May Dreams Gardens.

Spigelia marilandica
Spigelia marilandica, second bloom after deadheading a few weeks ago

Spigelia marilandica
Spigelia marilandica

Asclepias tuberosa
Asclepias tuberosa, also reblooming after deadheading

Asclepias tuberosa
Honeybee on Asclepias tuberosa

Clerodendrum bungei
Clerodendrum bungei, one of my beautiful monsters

Lobelia cardinalis
Lobelia cardinalis, still going strong

Aralia elata
Aralia elata has been dropping tiny white flowers all over everything for a month

Liriope muscari
When was the last time you took a close look at the flowers of Liriope muscari?

Begonia grandis 'Early Bird'
Begonia grandis 'Early Bird', my own early-blooming selection of the species

Hosta plantaginea
Hosta plantaginea, "August lily", night-blooming and wonderfully fragrant

Datura wrightii
Datura wrightii, last night

Datura wrightii
Datura wrightii, this morning

Datura wrightii
One more because I can't get enough of those daturas!

Ipomoea
Morning glory (Ipomoea sp.), growing as a weed

Sphaerorrhiza sarmentiana
Sphaerorrhiza sarmentiana (Gesneriaceae), blooming on my windowsill at work


Thursday, August 14, 2014

Southeastern Palm Society summer meeting

Southeastern Palm Society
Southeastern Palm Society members

Members of the Southeastern Palm Society were treated to a meeting last weekend at Plant Delights Nursery and Juniper Level Botanic Gardens in Raleigh, North Carolina.  It had been several years since my last SPS meeting, and I'm always looking for any excuse to visit Plant Delights, so I decided to drive from Washington, DC to Raleigh to attend the meeting.  (I was fortunate to make it in 5 1/2 hours this trip.  I've made the trip in 4 1/2 hours, but once it took almost 8 hours.  The less said about I-95 through northern Virginia, the better.)