Winter garden soil improvement

Vegetable garden soils ideally should contain 5% organic matter. If your soil is lacking, boost it during the winter season by planting a cover crop.

Cover crops are grown to produce green organic matter to turn under the soil. Along the Front Range, plant them from September to no later than mid-October. In addition to boosting organic matter, they prevent wind and water erosion over the winter, build soil structure and suppress weeds.

Legume cover crops can add nitrogen to the soil through the action of nitrogen fixing bacteria. It is good practice to buy rhizobium (beneficial root-associated or “rhizo” bacteria) and apply as specified if the seed is not rhizo coated. Rhizobium bacteria are specific for the legume species and are sold with a specific expiration date.

Broadcast the seed/rhizobium mix at the specified seeding rate and water to germinate. If irrigation systems are shut down, hand watering in the fall will help the crop establish before growth slows for the winter.

Winter ryegrass is often used alone as a cover crop (see photo). Winter rye/Austrian pea or a winter rye/hairy vetch mixture overwinter well in Colorado. Winter rye is a quick germinating and pioneering grass. Hairy vetch is a hardier legume than winter pea for the coldest areas. Seed winter rye and Austrian pea at 4 to 6 ounces per 100 square feet. Plan on 2 to 3 ounces of hairy vetch seed for each 100 square feet of garden area.

Note that these green winter plants are attractive to deer and geese. If they are well established prior to extreme winter temperatures, plants generally recover from winter grazing in spring.

When turned under, the decomposing green material can deprive spring vegetables of oxygen if not done far enough in advance of planting. Plan to mechanically till or hand spade under at least two weeks and better yet a month prior to planting. The legumes may have to be tilled several times to kill them and prevent resprouting.

Many gardeners do not have the land area to plant a cover crop for the growing season without depriving themselves of vegetables for a year. Winter cover crops solve that problem.

Consider planting a cover crop this winter to improve your soil.

Pick and ripen tomatoes when frost threatens

While warm weather can linger well into September along Colorado's Front Range, temperatures can also drop unexpectedly. The earliest September freeze in Denver occurred on September 8, 1962 when the temperature dropped to 31 degrees F. I’m certainly hoping for a warm fall but will be prepared to mount a tomato “rescue” if things look dicey.

Covering plants to trap heat from the soil is often enough to get through a short one or two night situation. Extended days of cold particularly when accompanied by cooling moisture (rain or snow) are more problematic. In those cases, harvest fruit before the frost event and ripen indoors.

Pick fruit with even a hint of color. Also harvest green tomatoes with a glossy green appearance that are at least three-fourths of their full size. Remove stems. Wash fruit under a stream of water and allow to air dry on clean towels. Make immediate use of any damaged fruit and save only blemish free tomatoes for ripening.

Low humidity causes fruit to shrivel while high humidity promotes mold. Pack fruit one layer deep in cardboard boxes in a room out of direct sun. Another option is wrapping individual fruit in sheets of newspaper or waxed paper if you have problems with shriveling.

Some gardeners have success with hanging whole plants upside down in a shed or basement to let fruits ripen gradually. In our dry climate, fruit handled this way tends to shrivel from low humidity.

Monitor fruit condition every few days. Remove fruit that has started to spoil before rots move to adjacent fruit. Ethylene gas produced by ripening tomatoes is a ripening hormone. Remove ripe fruit from the immature ones to slow ripening. Allow ripe fruit to remain to speed ripening of the rest of your tomato harvest.

Green fruit will ripen in about two weeks at 65 to 70 degrees F and about 3 weeks at 55 degrees. Storage below 50 degrees F will result in fruit with a bland, off-flavor. Never store tomatoes in the refrigerator if you want full flavor.

Photo credit: Range of tomato maturities on vine and Harvested tomatoes in box - Carl Wilson

Tomato bacterial spot

Tomato fruit in home gardens and commercial fields in Denver and the northern Front Range have developed a black spot disease unusual for our area. Dark specks from earlier in the season become raised and scab-like as they enlarge. Sunken centers on older spots are common (see photo left). Spots are brown turning black and can appear blistered. The round spots can merge causing irregular-shaped patterns (photo on yellow tomato below).

Bacterial spot is caused by a Xanthomonas campestris pv. vesicatoria (X.c.v.) bacteria. It is something we seldom see in our area due to our dry climate suppressing most bacterial diseases. This year, the wet early summer and higher humidity favored it. If people overhead instead of ground irrigated they tended to help the disease. The widespread hail and heavy, wind-driven rains that inflicted injuries on plants helped disease spread via wound entry.

At this point there is no way to make the existing spots go away. Early in the season, avoiding overhead watering would have helped. Clean plant debris from gardens and fields this fall. Don’t save seed as it can survive that way. Rotate tomatoes and peppers (another host) to soil growing non-tomato family plants (disease survives in soil for up to 1 year). Eliminate weeds in the tomato/potato family.

Other measures to spray transplants after setting out probably apply to humid climates as we may see little or none of this next year if it is drier and overhead watering is avoided.

This outbreak is a good example of an environmental trigger (rain and humidity) setting off a disease rarely seen even though the host plant and likely the bacteria were present in past years.

Note that the fruit is edible although many people may prefer to remove the skin with the surface spot.

Photo credits: Sunken spots red tomato – Carl Wilson,
Merged spots yellow tomato – Robert Cox

Powdery mildew on vegetables

The telltale talcum powder look of powdery mildew infections is common on squash and pumpkin vines now. This disease can cause yellow leaf patches on some plants, and distorted buds, stems and leaves on others. Leaves may drop prematurely and flower buds fail to open.

Powdery mildew damages plants by decreasing photosynthesis and removing nutrients from the host plant. Infections weaken plants and leave them vulnerable to other pests. Mildews are host specific and the ones seen on the vine crops will not affect onions or fruit trees.

It is generally thought that plants in areas with poor air circulation are prone to infection. Mildews are different than many other plant diseases and don’t require wet leaves for infection. Warmth and adequate humidity are sufficient. Dense plantings hold humidity on calm days and are often enough to set off disease development..

Do plant vegetables in full sun as shade contributes to weaker plants and also longer moisture retention. Prune or thin plants to increase light and air circulation. Direct water on the soil and don’t wet plant leaves. Avoid excessive fertilizer that promotes succulent leaf tissue that is more easily penetrated by disease organisms. Look for powdery mildew resistant varieties if available.

Most fungicides are preventives meant to be applied before disease appears or at least in the early stages. Examples are sulfur and potassium bicarbonate (sold as Remedy). Read label directions before application. With sulfur, be mindful that it can damage some melon and squash varieties. Do not apply sulfur when temperatures are at of above 90 degrees F or plant injury can result. In the photo right an eradicant stopped the disease and weather conditions were unfavorable for development so new growth is unaffected.

A few fungicides can kill existing mildew infections (eradicants) but are still best applied at the earliest sign of disease. The natural Neem plant-based fungicides (Greenlight Powdery Mildew Killer) and horticultural oils are eradicants. Don’t apply oil to drought-stressed plants or within two weeks of a sulfur spray application. Don’t spray oils at temperatures at or above 90 degrees F.

Thanks to Mary Small for information used in this post

Photo credit 4 powdery mildew photos, Carl Wilson

Winter squash and pumpkin fun

As summer moves into fall, peek in your neighbor’s gardens and see what type of winter squash and pumpkins they’re growing. They are often standouts for their color and size. I ran into this pumpkin and Turks turban squash arbor (photo) that looked like a space saver. Grow vines vertical rather than horizontal! The centuries old, flat, French “Cinderella” pumpkins (Rouge vif d'Etampes) are also fun (see photo). Now is probably the time to remove any new fruit set on winter squash and pumpkins so existing fruit can mature.

These vines need lots of space to have the many leaves needed to produce enough energy to grow these large fruit and generally require 90 to 120 days to grow. The gardener in this photo is fighting to keep her window wells from being covered by a pumpkin vine. Certain winter squash do come in bush or semi-bush varieties (acorn, butternut, delicata). Vine tips can be pinched to keep vines in bounds but will limit production and quality. It’s better to find a spot with room such as this streetside gardener (photo).

Winter squash differs from summer squash in that it is generally harvested and eaten in the mature fruit stage. Vegetable spaghetti (photo) is probably an exception often being harvested in a semi-mature stage (harvest when the skin turns from green to buff). Pick most winter squash when the skin has hardened into a tough rind not easily dented with light fingernail pressure. The seeds within should have matured unlike the young tender seeds in summer squash. When ripened to maturity, fruits of most varieties can be stored for use throughout the winter.

Winter squash are harvested in September or October, before heavy frosts. Carefully cut squash from the vines, leaving two inches of the often-woody stem attached if possible. Avoid cuts and bruises to the fruit when handling. Fruits that aren’t fully mature, are injured, have had their stems knocked off, or have been subjected to heavy frost won’t keep. Use as soon as possible or compost (watch for seedlings in the compost).

Squash are best stored dry at a temperature between 50 and 55°F. Don’t pile squash more than two fruits deep. Single layers that don’t touch prevent rots from spreading through fruit.

Don’t forget that squash and pumpkin seeds can be dried in a dehydrator or roasted for a healthy snack. When scooping out seeds to use the fruit, wash clinging fibers from the seed and dry or roast.

Photo credits: Squash arbor, Turks turban squash, Cinderella pumpkin, Pumpkin vines over window well, streetside pumpkin garden, vegetable spaghetti squash – Carl Wilson

Hail update and Early blight time

After the hail -
In my previous post about the July 20 hailstorm that hit the west Denver Metro area, I promised to report back to you. Here is the one month update.

Squash came back fantastically. The crooknecks sent two branches to either side and grew abundant new leaves (photo left). They also have been producing well (photo right). Compare to the photo published in the July 23 post. If the growing points aren’t completely destroyed, it’s obvious squash has a notable ability to bounce back.

The tomatoes are also on the rebound and maturing fruit especially the ‘Sweet Tangerine’ (see photo left). These annual vegetables have amazing resilience to plant-damaging hail events. Patience and water soluble fertilizer applications as discussed in the July 23 post can salvage a partially destroyed garden.

Early blight time -
Late summer is early blight disease time in the tomato plot. Infected leaves develop ½ inch, irregular brown target-like spots (photo below right - click photo to enlarge). As this fungal disease progresses, spots grow together causing lower leaves to yellow and drop. If severe enough, defoliation leads to fruit sunscald and decreased production. Warm temperatures, abundant rainfall, overhead irrigation, and high humidity promote disease development.

Fungal spores are splashed from overwintering plant debris and infected tomato family weeds such as horsenettle and nightshade. Volunteer tomato plants that sprouted from last years stray fruit left overwinter also can carryover the disease.

Manage the disease by eliminating volunteer tomatoes. Properly fertilize plants with nitrogen. Late season nitrogen deficiencies stress plants, making them more susceptible. Avoid working around tomatoes when leaves are wet. Brushing leaves can bruise them and the water aids spores in germinating and moving into leaf tissue. Irrigate at the base of plants rather than wetting leaves. Apply sulfur dust to protect uninfected foliage against infection. And finally, be sure to clean up garden debris thoroughly this fall.

While early blight can be manageable in late summer gardens and fruit can mature before frost, severe cases can limit production.

Appreciation is extended to Mary Small, Jefferson County CSU Extension Plant Clinician, for disease information.

[Photo credit Carl Wilson: Squash leaf recovery and squash fruiting 1 month after hail, ‘Sweet tangerine’ tomato fruit with white hail nicks visible on plants, early blight target spots and yellow leaves on tomato.]