Got mulch?

With the arrival of temperatures in the eighties and nineties F along the Front Range, it’s time to mulch the vegetable garden. Soil temperatures are now thoroughly warm and mulches will not prevent the soil warming sought in spring.

The use of mulches now has several benefits. It will blunt the force of hard summer rains minimizing crusting and soil compaction. Mulch slows evaporation and can reduce irrigation needed by 25 to 50 percent. Stabilizing soil moisture to avoid wide swings from wet to dry promotes better quality vegetables and encourages the activity of beneficial soil organisms. Mulches applied now tend to keep soil temperatures cooler during summer and suppress weed seed germination.

Weed and seed-free straw (left) and grass clippings make some of the best mulches. Wood mulches are not recommended around vegetable plants, only for paths in the garden. Collect grass clippings from lawns that have not been treated with herbicides (“weed killers”) for at least a month.

Apply a thin layer of grass clippings (right) which will dry in five to seven days (below), then add the next layer. Two to three layers is generally enough to suppress weeds. Do not add thick layers which will mat, smell and limit water and air movement into the soil. Carefully apply around leafy vegetables as grass clippings are difficult to wash from the leaves and heads of greens.

Both straw and grass clippings can be tilled under in the fall and easily break down to enrich the soil. If straw isn’t desired for tilling under due to appearance, it can be raked off and placed in the compost bin.


Straw and grass clipping mulch photo credit: Carl Wilson

Flowers and fruit set of cucumbers and squash

It's time or nearly so when the vine crops will produce their first flowers only to have them drop off. What’s going on?

Cucumbers, squash, gourds and pumpkins produce separate male and female flowers on the same plant. The male flowers on cucumbers (right) appear about 10 days before female flowers and outnumber female flowers 10 to 1. Squash, gourds and pumpkins bear 4 to 10 male flowers for every female flower.

Learn to differentiate male from female flowers, be patient until the female flowers appear, and watch to see if bees are present to move pollen between flowers.

Male flowers are attached by a straight slender stem. The stem of female flowers bears a bulge, the ovary, which grows into the future fruit if pollinated and fertilized. In the squash photo above, the two male flowers (left and center) have just faded for the day and are clearly borne on slender stems. The female (still green) flower on the right will open tomorrow and has the swollen stem bearing the ovary.

Male flowers produce nectar and pollen and female flowers nectar only and in greater quantity than male flowers. Bees gather pollen in early morning and switch to nectar later. Flowers open early in the morning and close by noon or shortly after the same day never to reopen.

Note that the flowers of many other plants produce more nectar and are more attractive to bees than the vine crops. While both honeybees and bumblebees can pollinate vine crops, they can easily get distracted by other flower nectar and fail to pollinate your cucumber or squash flowers. If fruit set is poor you can remove male blossoms, tear the petals off to expose the pollen on the anthers, and hand pollinate.

Cucumber and squash flowers photo credit: Carl Wilson

Strawberry time

June bearing strawberries are coming into their prime (photo right). June bearers fruit over several weeks and ‘Guardian’ and ‘Honeoye’ are good varieties. June bearers are less hardy than ever-bearing types so plant in the warmer cities of the Front Range. You can also mulch crowns in winter after the ground freezes with straw for protection. Like so many other perennial crops, winter watering is useful in dry winters.

Ever-bearers are dependable types for this area and hardier than traditional June bearers. They have two major fruiting cycles with sporadic additional production through the growing season. ‘Fort Laramie’ and ‘Quinalt’ are two commonly available varieties.

Another type to try is the day-neutral berries. They fruit in six-week cycles through the growing season. ‘Tribute’ and ‘Tristar’ are recommended varieties.

Strawberries perform best when planted away from wind in full sun of 8 hours duration. They are sensitive to crown rots so plant in well drained soil with crowns just above the soil. A raised bed with or without hard sides is an excellent growing situation.

I now see many strawberry patches bearing fruit and rewarding gardeners in Denver.

Photo credit – Strawberry fruit on June 10, Carl Wilson

Prepare for succession planting

Buy your seeds now to prepare for second plantings following harvest of lettuce, spinach, peas, kale and other spring crops. Bolting (seed stock formation) of cool season spring crops is a common sight following the first hot temperatures. See lettuce bolting photo left and spinach bolting photo right below. These plants should be cleared to make room for other vegetables to maximize garden productivity.

Planting of warm season vegetable transplants of tomatoes and peppers and seeds of squash , corn and beans may replace some of these spring crops now that soil temperatures have thoroughly warmed.

Do remember the mid-summer planting opportunity for fall crops of cool season vegetables. Early to mid-July is the time to seed your fall crop of kale, lettuce, peas and other approximately 60 day cool season vegetables. Even though they will be germinating and starting growth under high summer temperatures, they will be maturing in September when temperatures are cooling. Quality can be good as a result. Note that there is also a fall opportunity to plant leafy vegetables desired for early spring crops. See the Colorado State University Extension Garden Notes #719, Vegetable Garden Hints.

Shop for seeds now to have them on hand before seed supplies run out and seed racks disappear until next year.

Lettuce and spinach bolting photos credit, Carl Wilson

Planting, flea beetles and children

Late May is a busy time in Front Range vegetable gardens. With Memorial Day weekend rains (3 inches in my Denver garden), weeds are growing but easy to pull. Soil is moist for transplanting tomatoes and other warm season plants into the garden. It is also the time to direct-seed warm soil requiring plants like squash, beans, corn and cucumbers.

A visit to the West Washington Park community garden reminded me of several things. The first was how much the heat island effect of city centers has on advancing the season. Their gardens are about a week ahead of gardens in the outer parts of Denver due to the warmer temperature.

Second, early season insect pests are becoming active, foremost among them flea beetle. Germinated beans were already showing holes (photo above left) and upon closer examination, the shiny hopping beetles were present (palestriped flea beetle photo below).

Not only beans but tomato family and cabbage family plants are attacked among other vegetables. Watch young seedlings closely and take action before damage becomes too extensive. While mature plants can withstand some 10 to 20 percent loss of leaf tissue with no adverse affect, seedlings are another matter.

Trap crops such as radish are one good idea. Diatomaceous earth is an effective repellent, and several insecticides including the bio-derived spinosad are effective. Weekly reapplications are often necessary as new plant growth will be unprotected and insects are very mobile. For more photos and control recommendations, see the Colorado State University Extension Flea Beetles fact sheet.

The third reminder I received from my visit is to involve children in your vegetable gardening efforts. Now that school is out, choose age-appropriate garden activities for children and youth, whether they are yours or your neighbors. They will be the richer for early involvement in the garden and receiving the benefit of your presence in their lives.

Photo credits:
Flea beetle damage on bean seedlings, Carl Wilson
Palestriped flea beetle close up, Frank Peairs, Colorado State University, Bugwood.org
Children’s toys among beet seedlings, Carl Wilson

Raspberry pruning

Red raspberries are very hardy and grow well along the Front Range. Black and purple raspberries do better in milder climates like the fruit producing areas on the West Slope.

While raspberry clumps are perennial, individual raspberry canes should be removed after they have fruited once. In practice, this means that canes should be pruned out after either their first or second year. The trick is to know which year to prune.

The raspberries you have may be either summer (June) fruiting varieties, or fall bearing plants that produce a late summer/fall crop. Summer bearers flower and bear fruit on canes that grew the previous year. Once they fruit, those canes won’t produce a crop again and should be removed. Recommended summer bearing varieties are Latham, Boyne, Laura and Honey Queen.

Fall varieties bear fruit on new growth produced in the summer. Those canes will produce a light early summer crop the next summer. After that, the canes should be removed. Fall bearing canes can be cut down to the ground in early spring if an early crop of fruit isn’t wanted. Fall bearing varieties include Heritage, September Red, Fall Red, Red Wing, Amity, Pathfinder, Trailblazer, Plainsman, Perrone’s Red, Caroline, Autumn Bliss, Goldie and Anna.