Sunday, May 17, 2015

Cool, Wet Weather Persists

Freeze damage on tender grape leaves
The limp grape leaves in the photo show one effect of cool, rainy spring weather. Clearing skies on May 10 as a storm system moved out after a week of rain allowed temperatures to plunge below freezing overnight damaging tender new leaf growth. Reserve buds will need to grow to take the place of the lost leaf tissue. Leaves that had already fully expanded and hardened were not damaged.

If you are anxious to plant warm season plants this is a lesson in hardening them off first. Plants purchased at plant sales should be shuttled in and out of the house or coldframe for at least a week, out on warm days and in overnight or on cold days. Nighttime temperatures remain in the forties at mid-month, way too cold for tomatoes and the like. Soil preparation including fertilization and adding compost are good places to direct your efforts now.

Spreading compost on vegetable
garden to mix in 4 to 6 inches
Soil temperatures at 4 inches have crept up to 54 degrees F after plunging to 50 degrees F following a week of cloudy, rainy weather. Keep in mind that the minimum soil temperature for tomatoes is 50 degrees F. Planting is possible under Walls of Water that keep above-ground plant parts warm overnight. Better yet use them in combination with plastic mulch that also utilizes the sun to warm soil for roots to grow. The plastic can be removed in June along with the Walls of Water if you care to not leave in place for the season.

 For some vegetable gardeners warm season crops are the reason to grow a vegetable garden. Cool, rainy spring weather has made this more of a cool season vegetable gardener's year so far.

Delayed planting of warm season vegetables to closer the end of the month is likely a better approach for those not using Walls of Water and plastic mulch. For information on planting warm and cool season vegetables, see the CSU Extension "Vegetable Planting Guide."

Photo credit: Freeze damaged grape leaves, Compost application - both credit Carl Wilson

Monday, May 11, 2015

Warm Season Vegetable Transplanting and Plant Sale Recommendation

This past week we saw a week of rain ending with snow that dropped 3.3 inches of precipitation in my Denver garden. The wet week ended May 10th with an overnight low of 31 degrees F.
Two years in a row! Tomatoes in Wall
O'Waters on May 12, 2014.

Any early-transplanted warm season vegetables required protection with Walls O'Water or second best the use of frost blankets. Even so warm season vegetables will likely be set back and take time to resume growth. Cloudy weather during the week didn't allow much solar gain for Walls O'Water.

Planting thoughts this week should take into account wet soils. Give them time to dry to a medium moisture content before transplanting or seeding. Don't walk in or work soil when wet; you will only destroy soil structure if you do. Meanwhile, consider what warm season vegetable varieties you want to plant this year.

Vegetable transplants being grown
by Denver Master Gardeners for their
May 16 and 17, 2015 sale.
I'm impressed with the wide selection of vegetable varieties offered by CSU Extension Denver Master Gardeners at their spring plant sale this coming weekend. The sale is Saturday, May 16 from 8am to 3pm and Sunday the 17th from 10am to 3pm.

Location is the Denver CSU Extension office in Harvard Gulch Park, 888 E. Iliff Ave, Denver, CO. This plant sale promises to be worth a visit and proceeds benefit CSU Denver's education programs.

Click to download and then open this file for more information and a list of varieties offered at the sale: Denver CMG Spring Plant Sale.

Wednesday, April 22, 2015

Fruit tree freeze deaths

Subzero temperatures the second week in November did more damage than just preventing normal leaf drop (see Jan 16 "2014 Gardening Year in Review" post). As normal times for Front Range fruit trees to leaf out have come and gone, realization is dawning among home fruit growers that parts and indeed whole trees are dead. A warm fall did not allow trees to fully enter dormancy leaving them unprepared for the sudden, early subzero temperatures.

The row of sour cherries pictured have only a scattered bud or two alive. These few green buds will likely shrivel when summer heat arrives. Already gummy sap is oozing as a stress sign confusing some that peach tree borer is responsible despite the location higher in the tree than the soil line (no frass present either). See CSU Extension's fact sheet for information about Peach Tree Borer.

Few apple branches
 flowering/leafing on this tree

Not only cherry but in some cases generally hardier plum and apple trees show damage. In addition to fruit trees, damage of landscape shrubs and trees will become noticed more as the season progresses. Notable casualties to date include burning bush and spreading ('Manhattan') euonymus, rose, pyracantha, boxwood, privet, weigela, hibiscus, smoke bush, spiraea and buckthorn.

Wednesday, March 11, 2015

Fruit tree pruning time

Now that the worst cold winter blasts are hopefully over, dormant season fruit tree pruning should be completed in March prior to bud break. The pruned peach tree in the left foreground looks sparse compared to the unpruned tree to the right. This is as it should be.

Peaches put on a lot of growth and should be pruned hard. They bloom on 1 year old wood and if shoots are left for two years or more, they don't produce fruit. Much of last year's growth should be thinned out to avoid overproduction and allow light into the tree. Excessive fruit production reduces quality and also weighs down branches causing limb breakage.

To balance growth of fruiting wood with peach fruit production, remove one-half to two-thirds of last summer's growth. Space fruiting shoots 6 inches apart remembering to leave long shoots of 12 to 24 inches (they fruit better). On the interior of the tree smaller shoots can be left. Don't worry, you will have plenty of new shoot growth over the season to provide fruiting wood for next year's peach crop.

Little annual pruning is needed on fruiting sour cherries and plums. Bearing apples and pears require a light annual thinning for light penetration. Avoid removal of the short fruiting spurs. Unpruned trees may produce more fruit of lower quality for a few years, that is until growth gets so dense that fruiting on the interior ceases.

Train young trees for a sound structure in the first few years. Then maintain bearing trees with annual pruning for a productive fruit tree.

Friday, January 16, 2015

2014 Gardening Year in Review

Frost apparent on tomato leaves.
The best thing about 2014 was probably the extended growing season with the acknowledgment that many vegetable gardeners had to cope with hail along the way. Even though the first official freeze is recorded as October 3, lows weren't extremely cold on that date nor several times later in the month.

Temperatures dipped only into the low 30's F on Oct 3, 12 and 27 in Denver, well within the ability of frost covers to handle. The weather otherwise was warm enough to keep tomatoes growing late and certainly warm enough for mid-season planted greens and root vegetables to mature nicely.

This all came to an end on November 10 with a low of 13 degrees F followed by subzero F lows the next three nights. These temperatures are way beyond the ability of frost covers to handle and effectively ended the growing season for those using frost protection. True to life in Colorado's high altitude steppe climate, daily highs in the 50's and 60's were recorded the end of the month.

Cherry leaves retained through winter.
The unknown factor about this generally warm late growing season suddenly ended by subzero cold is the possible damage to fruit trees.  The most obvious sign of this now is the retention of leaves on apple, cherry and other fruit (and ornamental) trees. 

The cold obviously interfered with the normal leaf abscission process but less clear is how much damage might have occurred to buds and wood. This won't be fully known until spring when lack of bud break and dead wood will show us the extent of any freeze damage. Lack of gradually cooling weather to promote full development of dormancy can deal a crippling blow to fruit trees exposed to sudden subzero temperatures. Let's hope for the best.

Note for those interested in growing fruit trees, I will be teaching a new fruit tree growing class at Denver Botanic Gardens on March 14. See clickable link to DBG in the 2015 class offerings found in the right column.

Photo credit: Frost on tomato leaves, Leaf retention on cherry - both credit Carl Wilson

Monday, October 13, 2014

Season continues for some gardeners

'Azoychka' yellow tomato Oct 13, 2014
If you were lucky you escaped Oct 12 scattered frosts or covered tender plants and will be rewarded with an extended growing season. We've been in a pattern of cold-hot-cold-hot. This is expected to continue with temperatures again predicted to reach 80 degrees F in a couple days. Life in the high altitude, steppe climate of Denver, Colorado is always a roller coaster ride.

Tomatoes remaining on the vine will continue to ripen and zucchini will continue to grow larger. Just like betting when to plant warm season crops in spring, deciding when to shut down the warm season garden in fall is a challenge. I know some gardeners who have already torn out their gardens. How many more frost "escapes" will us late season garden gamblers have?

Zucchinis Oct 13, 2014
Of course tomatoes still on plants showing some color such as the yellow Azoychkas in the photo above may yet ripen on the vine. The ace in the hole is they are good candidates for picking and ripening indoors if a hard freeze is predicted (overnight temperatures expected to fall into the mid to upper twenties F). Green ones that are small probably won't have a chance but the largest can be harvested and used as fried green tomatoes.
'Bulls Blood' beet and 'Red Russian' kale
Oct 13, 2014

Meanwhile mid-summer planted, cool season crops such as the beets and kale in the photo will tolerate early frosts. The flavor of kale only improves once frosts begin in earnest. This is shaping up to be a year for warm season vegetable harvests to extend late into fall and cool season crops rewarding the savvy gardener with fall harvests as they always do.

Photo credits: Azoychka tomato, Zucchini, 'Bulls Blood' beet and 'Red Russian' kale all credit Carl Wilson.