Colorado’s fickle climate

A few weather observations this week. The Colorado climate never ceases to amaze me. September 19 and 20 had record highs for those dates, 96 and 94 degrees F respectively. Then on September 23, some low lying areas in Denver and open space areas on the outskirts had light frosts overnight. The following weekend another 90 degree F record high was set on the 26th. Be ready - temperatures can change on a dime or so it seems.

A visiting gardener told me this week that his cucumbers and other frost sensitive garden vegetables froze on Labor Day, September 6, during the last cold snap. His garden is in a low lying area in south-central Denver, not even on the outskirts of town. Clearing nights with radiational frosts combined with air drainage into low lying areas can catch plants earlier than most of the surrounding area.

As they say in real estate – location, location, location. This savvy gardener hedged his bets by cultivating plots in several community gardens that were unaffected. These low lying areas are bad bets for growing fruit trees.

It’s a good time to think about frost protection and season extenders now that fall is officially here. I admit to being biased but one of the best discussions I’ve seen on these topics is our CSU Extension CMG Garden Note 722, titled Frost protection and Extending the Growing Season. Review it for a refresher on how measures such as plant covers are used best


Diagram from CSU Extension CMG Garden Note 722.

Harvesting and storing pumpkins

Harvesting pumpkins seems pretty easy – wait until orange and detach from vine. It is and isn’t that easy depending on how long you want to store them.

Like many parts of the Upper Midwest, we seem to be having an early harvest season this year. Pumpkins and fall squash should be harvested when skin is tough and doesn’t yield to gentle fingernail pressure. Stems should be dry.

Research shows jack-o-lantern size pumpkins reach full color 45 days after fruit set and stems harden in 20-35 days after fruit set. This is for ideal growing conditions and may take longer if there is shade, drought, disease or other stresses.

Know that conditions both before and after harvest affect storage life. Vines that are healthy up to harvest make for a longer keeping pumpkin. Likewise, favorable storage conditions after harvest make a difference too.

Cut the stem with hand pruners to preserve stem health. Solid stems provide an effective barrier to rot. Use care in moving pumpkins to avoid nicks, scrapes and other mechanical injury. Move when the surface of the fruit is dry to be able to get a firm grip on fruit among other reasons. They keep better if harvested before frost and sustained periods under 40 degrees F.

Store in a shaded, dry area with good ventilation. The best storage temperature is 50 to 60 degrees F. This temperature is likely difficult for most people to achieve, particularly with hot weather lingering late into September this season.

Healthy fruit that is harvested and stored under favorable conditions can last up to 6 months. If you want fruit to last until Halloween, that is a reasonable goal. Storage until Thanksgiving will take a little more attention to each step of the growing and harvesting process.

Photo credit: Standard and flat French pumpkin types – both Carl Wilson

When are watermelons ready?

I never used to be a fan of growing watermelons in northern climates. Years ago available varieties never reached maturity and tasted bland or green. Newer short season watermelons have changed all that. Varieties such as ‘Sugar Baby’ (75 days), ‘Shiny Boy’ (75 days), ‘Yellow Doll' (76 days), ‘Blacktail Mountain’ (70 days) and others have a reasonable shot at maturing in our short growing season. They should be transplanted like many warm-season vegetables so seed your own indoors in spring or purchase transplants.

A frequent question I receive is how to tell when watermelons are ripe. You can gently roll the melon over to check for a yellow groundspot. Another clue is to look for the curled tendril below the vine attachment. Green tendrils indicate a green melon while a shriveled, brown tendril indicates maturity.

Then there is the sounding method. A knuckle tap that yields a dull sound indicates under-ripe. If it sounds hollow, the watermelon is ripe for eating. A soft sound indicates over-ripe. This method also works in the produce market.

Tapping knuckles takes on a whole new meaning for cool vegetable gardeners.


Photo credit: Watermelon on vine – Carl Wilson, ‘Shiny Boy’ watermelon – 2010 All America Selections winner.

Plan now to ripen tomatoes

The first week of September brought four nights with temperatures in the forties to Denver. Tuesday morning following the Labor Day holiday I was surprised to find frost on the grass in the open space area near me in Southwest Denver (no frost in the residential area nearby though). Seasons change quickly on the Front Range making this a good time to plan to get the most from summer tomato growing efforts.

Newly setting tomato blossoms, small and very green fruit won’t mature in the remaining growing season and are best pruned off. New, vigorous shoots also may be clipped back. Don’t remove an excessive amount of leaves as these supply nutrients to fruit. Light pruning directs plant energy to fruit that has a chance of maturing.

When fruit set is heavy, it can work against gardeners. Ripening numerous fruit takes a lot of energy from the leaves and tends to delay the whole crop turning red. If there are only a few weeks before frost and fruit is not ripening, try removing some of the mature green fruit to ripen what’s left on the vine.

Cooler September temperatures help fruit to ripen because the red tomato pigments, lycopene and carotene, are not produced above 85 degrees F.

As late September approaches, gardeners often try to extend the life of their plants by covering with cloth or plastic. Covering plants works well for nearly red tomatoes, but not as well for mature green ones. Research shows that chilling injury on green fruit occurs at temperatures of 50 degrees and decay losses are heavy on fruit exposed to 40 degrees F. Red ones well on their way to ripening better tolerate colder temperatures.

Before frost hits and plants go down, pick and bring fruit indoors to ripen. Extended exposure to cool temperatures interferes with ripening and flavor development. Clip fruit to leave a very short stem piece but not so long to punch holes in other tomatoes. Stems ripped out of fruit will open them to decay.

Eliminate young, green fruit, as research shows it’s more likely to spoil than ripen and never develops the flavor consumers want anyway. Mature green fruit will develop good flavor. Mature green tomatoes are well sized and have turned light green to white.

Sort and store fruit in groups that will ripen at similar speeds. Fruit may be “mature green”, "turning" with a tinge of pink to "pink" with 30 to 60 percent color showing, "light red" with 60 to 90 percent color present, and others "fully red" but not soft.

Store ripening tomatoes at 55 to 70 degrees F. Refrigerator temperatures of 40 degrees are too cold to ripen mature green tomatoes and are colder than desired for ripe ones. Ripening enzymes are destroyed by cold temperatures whether in the garden or in a refrigerator.

Ripen tomatoes in well-ventilated, open cardboard boxes at room temperature checking them every few days to eliminate those that may have spoiled. Mature green tomatoes will ripen in 14 days at 70 degrees F.

Cold weather and frosts can come in late September before typical October killing frosts arrive. Plan now to realize the biggest harvest from your vegetable garden.

Photo credit: Roma tomato with mature green fruit, Staked tomatoes, Tomato harvest in box - all Carl Wilson

Harvesting and ripening pears

The best way to tell when fruit is ready to harvest is often the simple taste test. For backyard gardeners not concerned with shipping fruit, this is good advice for apples, peaches, plums and grapes.

Pears are the exception. “Tree ripened” pears will not be satisfactory. Pears left on trees ripen from the inside out and stone cells fully develop making for “gritty” eating. When the outside is ready, the inside is often brown mush. If picked slightly immature, they ripen uniformly with a smoother flesh consistency OFF the tree.

Harvest most European pears such as ’D'Anjou’ (photo above) and 'Bartlett' when they easily detach from trees. Tilt them upward to horizontal and they come loose when ready for harvest. ‘Bosc’ pears (photo right) are always difficult to separate from the tree and stems may have to be clipped with a sharp pruner. All pears should feel hard when picked.

In looking for signals for when to harvest, disregard the red blush on varieties that develop it such as D'Anjou (photo above). The ground color of the pear skin will change to more closely resemble the mature pear of that variety. With Bartlett, D’Anjou and other yellow pear varieties, skin becomes a lighter green.

Pears then have to be ripened indoors. Some pears such as D'Anjou require cold storage before ripening. Bartlett does not but 2 days of chilling may help even ripening. D’Anjou and Bosc should be chilled for 2 weeks in the refrigerator away from apples, onions, potatoes and other fruits and vegetables. Pears in grocery stores and those shipped by specialty mail order companies have already been given their chilling treatment.

Ripen at room temperature, 65 to 75 degrees F. Warm temperatures of 85 degrees F or higher interfere with ripening. Bartlett pears generally ripen in 5 days, Bosc in 7 days and D’Anjou in 7 to 10 days. The longer pears are chilled, the shorter the ripening time when removed from cold storage.

Pears naturally produce ethylene gas inside the fruit as they ripen. You can shorten ripening time by placing pears in a closed paper bag with a ripe banana or apple, both of which produce ethylene to speed ripening.

Pears are ready to eat when the flesh just below the stem yields evenly to gentle pressure.

Photo credit: d'Anjou pears, Bosc pears - both Carl Wilson