A season of contrasts!

Originally published in the Davis Enterprise February 23, 2006

1/3/06: My how wet it’s been!

10.5” of rain since December 1! 5” around New Year’s! Our average December rainfall is 2.8”.  There was localized flooding and standing water in some orchards and gardens. Any concern about long-term damage to trees? Not really. The soil fungi that attack trees through the roots and crown (stem) are active in warm weather. Dormant tree roots can be underwater for 24 hours or more without concern in the winter, while similar conditions in July could kill them.

2/14/06: My, how warm it’s been!

Record or near-record warm temperatures since Feb. 7, highs in the upper 60’s to low 70’s. Nighttime lows in the mid to upper 40’s for ten days prior to that. No frost since Jan. 20. Spring is here! Time for tomatoes?

Longtime gardeners know that we always get a ‘false’ spring in February. But this was warm enough to get the subtropicals resprouting, get the roses growing, bring some spring flowering bulbs into bloom a couple weeks ahead of time, and spark the first thoughts of summer vegetable gardening. Early warm weather is rarely a concern. A subsequent frost might nip early growth on subtropicals, but that’s about all a gardener needs to worry about.

But some plants actually need a good winter chill to go through winter dormancy, then bud out and flower properly. Deciduous fruit trees, lilacs, peonies, and some other plants from northern latitudes have specific “chilling units” for the number of hours between 32 and 45 degrees (F). This is often expressed as “chilling hours”, and varieties differ individually. Most that we grow here need 500 – 800 hours, and as of Feb. 2 we had 550 – 600 in Davis; even less in Capay Valley: just over 300 in Esparto, 450 in Bryte.

What happens if a tree doesn’t get its chilling requirement? The flowers open slowly, sometimes don’t open properly and may not develop at all.  Leafing out is delayed (“delayed foliation”). Fruit set may be poor, production erratic, and quality poor. Many apple varieties, some cherries, and pistachio nuts are a particular concern. Among ornamentals, peonies and French hybrid lilacs simply may not flower well. Mulch them with ice cubes a couple of times to help them along. I’m not kidding.

2/15/06: My, how cold it got!

Near-record cold temperatures were felt throughout the valley and over on the north coast (29F in Fort Bragg!), as a very cold Canadian air mass moved down over our region. This kind of freeze in late December could have been very damaging. Coming later in the season, it wasn’t cold enough to do major damage. But this is why we don’t recommend cutting back frost-damaged subtropicals until March or early April. Bougainvilleas, young citrus, bananas, Hibiscus, and others may have thought it was time to regrow. But now that new growth has been nipped off. Leave them alone until warmer weather is here to stay.

The hardy fruit and nut trees and their ornamental relatives (almonds, plums, pears) that were in bloom were unfazed. The frost did some aesthetic damage. The early flowering Saucer magnolias (Magnolia soulangeana) were in full bloom, and the petals were toasted. Camellia blossoms may look burnt on the upper petals. Of particular concern would be some flowering potted plants you may have received as a Valentine’s Day gift. Flowering bulbs such as tulips and daffodils were not affected by the cold. But the hydrangeas, gardenias, and other flowering shrubs commonly sold as gift plants were greenhouse grown. If they were outside there may be some damage to the foliage, and the flowers were likely ruined.  Move them to a warm spot, trim off the spent blossoms and give them a shot of fertilizer.

Decide where the plant is going to live now: gardenias want a warm location, hydrangeas want partial shade. Miniature roses are far easier in the ground or in a large tub than in the small pots they come in. Once the weather has warmed, consider repotting (gift plants are almost always very root bound) or planting your shrubby flowering gift plants in the ground.

Plant retailers have a basic conflict of interest at this time of year. The growers have lots of lovely plants available, and warm weather brings out the gardeners. Coastal and southern California growers especially have lots of nice flowering summer plants available. Time for Impatiens, Begonias, marigolds? Not really. If you need a spot of quick color in your garden, stick to the cool-season annuals: pansies, violas, snapdragons, and more. Bougainvillea, Mandevilla, Brugmansia? The young plant won’t appreciate going in to cold soil. Put in these heat lovers in late March or April, or anytime through the summer.

Citrus growers are shipping the young trees at a rapid pace, with availability of some varieties already limited. A quick check with Four Winds Growers in Winters, one of the pre-eminent citrus growers in Northern California, found mandarins and limes already selling out. Customers get in the mood to plant fruit trees because this is when deciduous fruit trees are available “bareroot”—dormant, and inexpensive – in nurseries.  Citrus aren’t sold that way, since evergreen trees don’t go dormant.

But young citrus don’t benefit from early planting. I believe that citrus planted into cold soil will develop more slowly than a tree planted later in the season. And being subtropical, citrus trees root and grow quickly when planted even in mid-summer. So don’t worry: the growers will have more, and there’s no hurry on getting your orange or lemon tree planted!

2/17/06: My how dry it’s been!

No measurable rainfall since January 18. Do we need to water? Water use by plants remains very low, and there is plenty of moisture in the soil from the December rains. This would be a good time to run your sprinklers for a few minutes to see if heads need cleaning, flush your drip systems, and change the battery in your sprinkler timer. But regular irrigation of established plants is not necessary yet, and usually not until late March or April.

Exceptions: newly transplanted shrubs, trees, and flowers, and plants in containers, should be checked every few days for watering. Newly planted bareroot plants—fruit and shade trees, roses, lilacs—must be watered daily unless it is overcast or raining! The most common cause of failure of bareroot plants is inadequate watering during the critical period when roots are developing: February and March.

Too hot, too cold, too wet, too dry?!

Where can you keep up to date on garden-related weather issues? The Davis Garden Show, which I host with Lois Richter, is on Davis’ own KDRT 101.5 FM every Thursday from noon to 1:00, and repeated on Saturday mornings from 9 – 10. We start each week’s program with a weather update, and your calls and questions are welcome. Miss a show? You can download it to your computer, or even set it to download automatically (“podcast”) by going to http://redwoodbarn.com/podcast.htm.

[Update: since this article appeared we had a record number of rainy days in March, and unseasonably cold, rainy weather continued into April…]

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