Prospects for Fruit this Year in Denver

The 2015-2016 winter in Denver was unusually mild for fruit tree flower bud survival with only two days of zero degrees F (December 17 and 28) and no temperatures below zero (National Weather Service DIA records).

February 2016 brought enough warm days that fruit trees with a low chill requirement and low growing degree hours to reach bloom such as apricots and peaches were in flower by mid March.

Apricot in bud March 5

Apricot in flower Mar 19
with snow on branch

March brought fifteen days with minimum temperatures 28 degrees F or below. Overnight lows were 20 degrees F on March 19th and 10 degrees F on March 24. As a rough guide, 28 degrees F is the low temperature where many flower buds showing color or in bloom can be damaged. Prospects for apricot and peach fruit this year are likely poor.

Apple blossoms April 24

April has brought warmer nights. Since April 1st when the overnight low was 25 degrees F, the minimum temperature has not dropped to 28 degrees F.

This means that late blooming fruit such as apple and pear, and even fruit that bloomed slightly earlier such as sour cherry and plum may have fruit this year. Note that the specific location of fruit trees, localized overnight minimum temperatures, health of trees and amount of bee pollination activity are some of the factors that will affect your prospects to develop blossoms, set and grow fruit.

Photo credit: All photos credit Carl Wilson

Turning Under the Winter Ryegrass Cover Crop

As I was strolling the grounds of Denver Botanic Gardens this week enjoying the spring bulb bloom, I saw gardeners turning under a plot of winter ryegrass. This reminded me that cover crops aren't only used in vegetable growing. They can be used anywhere soil improvement is needed including for annual ornamental plantings at DBG.

Growing cover crops has enjoyed a recent rise in popularity in farming as concerns about soil loss have increased. The resulting increase in organic matter from growing cover crops helps in many ways. These include an improvement in soil structure and resistance to erosion, better water penetration and holding, increased soil biological activity, better plant nutrient holding and more. Home and market vegetable gardeners should seriously consider the benefits of cover crops in their efforts.

When growing winter rye for the first time one important question is when to turn it under. Consider this question from two standpoints: 1)how to get the most benefit and least drawbacks in the burial operation, and 2) when you want to plant your vegetable crop.

"Growback" (resprouting)
after turning under

Winter or cereal rye is best turned under when it is between 12 and 18 inches tall and relatively succulent. If turned under when short and still in a vegetative growth stage, there is a pronounced tendency to "grow back" meaning more work in burying plants a second time.

If left to grow until taller than 18 inches, rye enters the reproduction (flowering) stage and tends to have a high carbon to nitrogen ratio due to the high cellulose and lignin content that develops to stiffen stems. This means the plant parts you bury in the soil can be slow to decompose. Note that not only plant height but more so day length promotes flowering. Winter rye flowers when days reach 14 hours in spring.

Chop leaves into small chunks that are easy for soil microbes to attack and digest. In my small home garden plots I use a hedge shears cutting off 2 to 3 inch lengths from the top of the plant and working my way down to the soil line. You can also use a string trimmer to chop plants before incorporation into the soil. Chopping tends to minimize "grow back" because the food supply is cut off from the roots.

The second consideration in when to turn under a cover crop is when you want to plant. Allow a minimum of a month for the leaves and roots to break down before seeding or transplanting. This allows soil nitrogen availability to stabilize after being temporarily tied up by the soil microbes

chewing through the freshly buried rye plants. Once broken down, soil microbes release the nitrogen they tied up making it again available to plants.

Now is generally the time to turn under your winter cover crop if you are planning to plant warm season vegetables in late May or early June.

Photo credit: All photos credit Carl Wilson.