Season Endings and Beginnings

Vegetable Endings
With night temperatures predicted to drop into the thirties F this coming weekend, it's time to harvest what remains of tomatoes, peppers, eggplants and many other fruiting vegetables. Thirty degree temperatures are flavor killers for tomatoes anyway so using ripe fruit and ripening mature green or pink breaker fruit indoors is preferable.

Cover Crop Beginnings
Clearing plant refuse off the growing area now has another advantage. Mid-October is a good time to plant winter cover crops for soil improvement. Maintaining desirable levels of both organic matter and nitrogen in your soil is important for growing vegetables. Nonlegume cover crops help with organic matter and legumes can add both.

One common cover crop planted in our area is winter rye but there is a lot of confusion about what that is. Winter rye is cereal rye, Secale cereale, the same rye used for grain. Annual or Italian ryegrass, Lolium multiflorum, can be used as a cover crop in certain circumstances but winterkills in cold, dry Front Range conditions. Annual rye should be sown in early fall, so it's now late to plant.

Winter rye on the other hand is one of the hardiest of cereals and can be seeded later in fall. Growth is rapid in cool fall weather and its quick-growing, fibrous roots hold soil and leftover fertilizer well. It is also good at suppressing weeds.

Rye can also be sown with legumes in fall. Hairy vetch, Vicia villosa, is one of the most popular. It's winter hardy to zone 4 and can work in zone 3 with snow cover. It grows slowly but root growth continues over winter and vine growth quickens with arrival of spring. It tolerates poor soils (including sandy ones) and delivers a heavy contribution of nitrogen compliments of it's symbiotic nitrogen fixing bacteria.

A type of field pea (Pisum sativum subsp. arvense), Austrian winter pea, can also be used as a winter legume. It is not as cold hardy as hairy vetch and should be seeded in early fall. Plant it with a winter grain such as rye to protect pea roots and maximize winter survival. It prospers best with some winter moisture.

A rule of thumb is to plan for at least a month in spring after turning under cover crops to allow them to decompose before planting vegetables.

Photo credit: Tomato harvest and Rye/Hairy vetch seed - both Carl Wilson

Other root vegetables - parsnip

Parsnips are just now coming into their own with no need to worry about rushing to harvest before frost. In fact freezing actually improves root quality so bring on the cold weather. Roots can be dug as needed or stored moist (vented plastic bags) in the refigerator for a couple weeks so starches are converted to sugar for roots to have a better flavor.

Parsnips are grown from seed planted in early spring (April). 'Harris Model' and 'All American' are two standard varieties but most should grow well here. Fresh seed is a must as old seed germinates poorly. Like their parsley family cousin, carrots, seed takes 2 to 3 weeks to germinate. Seed is often over-planted because of poor germination and then seedlings thinned to 4-6 inches between plants.

This is a full season crop averaging 110 to 120 days (4 months) to mature. A deep, loose soil is a must just like carrots. Once top foliage grows to cover over, most weeds should cease being a problem. Supply steady moisture to avoid root disorders but note overwatering can cause forking and hairy roots. Moisture fluctuations produce cracking. Organic mulches (grass clippings or straw) in summer are helpful for weed and moisture control.

Parsnips are a different root vegetable to try for a variation from carrots and beets.

Photo credit: Parsnips in raised bed, harvested parsnip roots - both Carl Wilson

Seasonal roundup

Powdery mildew
With cooler weather comes a decline in production of summer squash and increase in powdery mildew on both summer and winter squash. Hopefully many fruit have been harvested or are near-ready for harvest. Photo is of powdery mildew on Kabocha winter squash. Powdery mildew decreases photosynthesis and weakens plants affecting nutrients available to form fruit and their flavor.

Control is mostly preventive through a full sun location and good air circulation. Water at the soil level rather than on leaves. Potassium bicarbonate (Remedy) can be used as a preventive or in the very early stages of infection. Some fungicides such as neem (Greenlight Powdery Mildew Killer) and horticultural oil do have some effect on killing existing infections.

Cabbage aphids
They're back......! Cabbage aphids thrive in cool fall weather and can be a real problem on savoy cabbage and Brussel sprouts (photo). They penetrate in and among the curled leaves and where sprouts set down in the leaf axil. Their feeding distorts and contaminates the harvest. Cabbage aphids overwinter on wild mustard family plants so weed control near the growing area is important.

Control is tough because of their waxy covering that makes these gray-green aphids appear bluish-white. Lady beetles don't like them because of the wax. Syrphid flies are another predator that may help. Unfortunately the activity of predators decreases late in the season when short days and cool temperatures reduce the activity of natural enemies. Parasitic wasps aid the cause but parasitized aphids tend to tightly stick to foliage compounding contamination problems.

Botanicals such as azadirachtin insect growth regulator, neem oil or pyrethins can be tried as well as horticultural oils when insect population thresholds warrant applications.

Destroy crop residue after harvest to minimize overwintering populations.

Photo credit: Powdery mildew on Kabocha squash, Cabbage aphid on Brussel sprouts - both Carl Wilson

The big cool down

In our semiarid climate, it's always amazing how fast the weather can cool down as the days shorten. Some folks I talked with the last week of August were despairing that it would cool down anytime soon. Then, wham. The first of September was officially 96 degrees F in Denver with a 68 degree low. By the 3rd it was 71 degrees with a 48 degree low.

The losers in the vegetable garden are the warm season vegetables. Tomato fruit have slowed ripening and summer squash are not producing fruit seemingly overnight. The winners are the cool season vegetables for those who had the space and foresight to seed them mid-summer (July).

Nights under 55 degrees F will cause tomatoes to shut down for a few days to a week, especially with nighttime temperatures reaching 41 degrees F, the official low on Sept 4th. Mature fruit on these plants will eventually ripen but the cold affects flavor. New and young fruit tend to stop development.

This is the time to think about season extension growing tunnels if you want to keep these crops producing through the fall. When temperatures drop 14 degrees below the desired 55 degree nighttime, tunnels almost have to be plastic on hoops as row cover fabric only provides a few degrees of difference.

Even though these temperatures are ten degrees below normal and we will likely still see some warm days, more nights in the forties are predicted over the next week. The cool season leafy vegetables like lettuce, spinach and kale are loving the temperature change to cool and don't need season extenders in early fall.

Photo credit: Two types of kale and lettuce - Carl Wilson

Beet leafminer

Beet or spinach leafminer is generally more of a cosmetic pest on beets grown for roots. For greens, it is another story.

The leafminer is the larva of a 1/4" gray fly with black hairs. Eggs are laid on leaves or several plants including beets, spinach, chard and weeds such as lambsquarters. Small maggots emerge and tunnel between leaf surfaces. The narrow tunnels merge into pale blotches (photo) and damaged leaves are distorted. Maggots drop to the ground to pupate and change into adult flies.

Leafminer emerges in April and May and several generations occur each year. They are active now on spinach and beets planted mid-summer for fall harvest and particularly common in gardens where one or the other crop is continuously grown.

Eggs are distinctive (photo) because they are white and laid in small masses. One of the simplest means of control is to check for egg masses and hand crush. Pinch leaves to kill karvae inside when mining is observed. Leaves with actively growing larvae also can be picked and destroyed or bagged for trash to be taken off site. Leaving picked leaves on the ground allows leafminer to complete its lifecycle.

The use of floating row cover fabric can help if put in place before flies emerge and the crop is in a different garden area than the previous year. You don't want flies emerging from the soil under rowcover with their favorite food handy and protected.

Control weeds around the garden and rotate crops for control.

Photo credit: Leafminer blotches on beet leaves (Carl Wilson), Leafminer eggs (CSU Extension)

Banner year for tomatoes

Although many people on the Front Range may be tired of summer heat, there is always a plus side. One is that it has been a banner summer for productive tomatoes. This is due to hot days but more so to warm nights. Many nights have been in the sixties degrees F instead of fifties as is so often the case in Front Range summers.

After a cool May and transplanting better delayed until the first week in June, some people were despairing of realizing a tomato yield due to a late start. This has obviously resolved itself and many varieties are showing good performance.

In full sun, 80 day heirloom 'Cherokee Purple' in our garden is doing as well as 73 day modern 'Big Beef'.

Three short season varieites tried this year are of note. 70 day 'Azoychka' from Russia (photo above right) is a mild acid, yellow fruited type that is producing well. A 68 day pink Asian type, 'Zhefen Short' (photo left) from China is yielding a good crop of nice plump fruit. The heirloom 75 day 'Black Cherry' (photo right) is also bearing nicely.

Shorter season types of 70 days or less including 'Early Girl' (62 days) and heirloom 'Stupice' (52 days) from Czechoslovakia (photo right) are still good bets especially if you have only part day sun or a cooler location. They bear early and can perform well in summers that don't have warm nights. Both have produced well for us this year.

Harvest from the demonstration garden at our Denver office is donated to feed the hungry. Consider donating your excess bounty to a local food pantry or soup kitchen.

Photo credit: 'Azoychka', 'Zhefen Short', 'Black Cherry', 'Stupice' tomatoes - All Carl Wilson.