Thursday, April 28, 2016

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

Sunday, April 24, 2016

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.

Monday, January 4, 2016

Cover crops for a green winter vegetable garden

Winter rye/Austrian winter pea
Fall planted cover crops make me feel good for two reasons. First I know that after they grow over the winter and I turn them under in the spring, I will have improved my vegetable garden soil. Second is the novelty of looking out my window in the depths of winter and seeing green plants in my vegetable garden.

Plant cover crops in fall from mid-September to mid-October on the Front Range of Colorado. With this year's warm fall weather you probably could have planted through the end of October. The season before we had subzero weather the second week in November so late plantings likely would not have survived. Plants require at least a month of moderate fall temperatures to establish before winter cold slows growth and soil temperatures drop below 40 degrees F.

Winter rye/Austrian winter pea or winter rye/hairy vetch mixtures work well for the Front Range. Many gardeners plant winter (cereal) rye. Grass (the winter rye) alone works well for increasing soil organic matter but if you want the advantage of the nitrogen adding abilities of legumes, add winter pea or hairy vetch in a mixture. Hairy vetch is hardier than winter pea and winter rye is very hardy. Plant at 4 to 6 ounces per 100 square feet except a lower rate of 2 to 3 ounces for vetch.

Water at planting and perhaps once or twice more to establish. In general winter snows will provide enough moisture for plants although you could always winter water in extended warm, dry winter weather if you feel you need to.

In spring spade or till the crop under the soil burying both tops and roots. Keep in mind that after turning under your cover crop you should wait a month for plants to break down before planting vegetable seed or transplants. If you need the garden space to start spring crops and don't have a month to wait, harvest cover crop plants and coarsely chop to decompose in the compost before adding them back to the garden soil between your spring and summer crops.

Cover crops should be a routine part of maintaining a healthy and productive garden soil. Online sources for cover crop seed include Johnny's Selected Seeds and Urban Farmer Seeds.

Photo credit: All photos credit Carl Wilson.

Saturday, June 20, 2015

Greens crop replacement

Buckwheat seedlings following
harvest of spring lettuce crop
The onset of ninety degree F weather along the Front Range means those cool season greens that have lasted so long this year due to a cool May will soon be gone. The heat decreases quality (bitterness), long days induce bolting, and the crops days to harvest may have just ticked by.

What to do now? In late June to mid-July you can begin planting mid-season crops for late summer or fall harvest. Some crops tolerate heat well such as Swiss chard, bush beans and New Zealand spinach. Collards can be planted up to 3 months before frost by direct seeding. Root crops that mature in 50 days such as beets and carrots are also good bets.

With other vegetables it is best to chose heat tolerant varieties. With lettuce the Cos (Romaine) types as well as others noted for heat tolerance (such as 'Muir' cultivar Batavian type lettuce) can work. Note that lettuce seed has a natural thermal dormancy and seed may not germinate well at high temperatures. Pre-germinate seed, plant in cooler weather and use irrigation to cool soils to obtain germination.

Likewise with spinach look for heat tolerance such as in the Asian arrowhead types; one example is 'Flamingo' cultivar.

Keep in mind crop rotation when second cropping, rotating to a crop from a different plant family. In addition to edible crops, remember you can also utilize a summer green manure (soil building) cover crop such as buckwheat, Fagopyrum esculentum. Turn under in 30 to 40 days as it starts to flower to increase soil organic matter.

Photo credit: Buckwheat seedlings - Carl Wilson

Thursday, June 4, 2015

Heat At Last

New grape growth
The average May 2015 temperature in Denver was 4.1 degrees below normal at 53 degrees F. The cool month slowed or delayed growth of some plants and postponed planting of warm season vegetables.

This first week of June turned hot with temperatures in the eighties F. With this warmth grapes finally began to grow in earnest. The late start means flowers will likely escape frost when they come into bloom shortly. This is good news for looking towards fall harvest.

Transplants of squash
and pumpkin vine crops
With increased sunshine soils have warmed over sixty degrees F and vine crop vegetable transplants can be planted.

Warm weather also means it was time to add water to the side channels of Walls O'Water (WOW) to push the tops open. This turns the structure into more of a cylinder than a cone and allows for ventilation while still keeping the plant warm at night.

Wall O'Water with more
water added to open top
into a cylinder
Keeping the WOW on tomatoes or other warm season vegetables is likely wise for another reason. May and June are active storm months for Denver and the Front Range meaning not only rainstorms but also the possibility of hail. WOW offer fairly decent protection from hail.

An understanding of temperature, it's effect on plant growth and what can be done to temper it is a must for gardening success particularly at our high elevation.

Photo credits: Grape growth, Vine crop transplants, Wall O'Water - All Carl Wilson

Wednesday, May 27, 2015

Still Useful to Plant in Wall O' Waters

Denver is receiving more sun and temperatures have warmed this week. That doesn't mean that it is ideal weather for planting tomatoes and other warm season vegetable transplants. Nighttime temperatures are still falling into the forties, far below the 50 F (and better yet 55 F) degrees nighttime temperature requirement for tomatoes. Note that the vine crops (squash, melons, pumpkins, etc. require 60 F degree nights).

A week after water channels filled at 
setup of Wall O' Water, sun has warmed water
sufficiently for planting within WOW cone. 
Plant deep for rooting along stem of this leggy 
tomato transplant.
So what's a gardener to do? You may have raised tomatoes from seed on your windowsill or purchased at a plant sale and the transplants are getting leggy. This is where Wall O' Waters come to the rescue. Even though often thought of for use in planting in the garden in April, they are still useful now.

Unlike mid-May when cloudy skies provided little solar radiation for heating the water in the tube walls of the Wall O' Waters, we are now receiving more sunlight. This provides warmth at night offsetting still cold night temperatures. Planting in Wall O' Waters also provides protection from wind and a sheltered environment for recovery from transplant shock.

Another benefit is protection from hail until plants grow above the walls. Even then plants pruned to the top of the Wall O' Waters by hail will retain enough undamaged plant within the Wall O' Waters to regrow.

If warm season transplants are planted in the open now without protection, they recover from transplant shock slowly and become stunted. We are assuming that night temperatures remain above freezing. They will require a week or more to recover from cold night stunting even when night temperatures warm above 50 to 55 degrees F in June. Although plants are leggy, you may be better off keeping them in pots and bringing them indoors at night until night temperatures warm if you aren't using Wall O' Waters.

See the manufacturer's website for more information on Wall O' Waters. Look to purchase them at your favorite local garden center.

Photo credit: Leggy tomato transplant for planting in Wall O' Water - Carl Wilson