'Niwot' fall bearing black raspberry released

Niwot black raspberry (US PPAF) - Photo by Pete Tallman

There is good news for Front Range small fruit lovers this year. Black raspberries (note we are not talking blackberries, a different crop) have not been recommended for this area before now. Recommendations have been to only grow red and yellow raspberries because of cold hardiness issues with black raspberries.

Longmont amateur plant breeder, Pete Tallman, has released the first fall bearing black raspberry recommended for the Front Range. Niwot has at least zone 5 hardiness and possibly greater.

Why is this a big deal? Now we can grow black raspberries that will fruit on first year canes in the fall. Before now the black raspberries available fruited on second year canes (summer types) and those canes were not hardy enough to reliably survive into the second year here. With Niwot, you can grow and harvest all in one growing season, cut canes to the ground in late winter and repeat.

Niwot was selected to be self-fruitful (no second variety required for pollination) and have good production of large fruit with small seeds. Fruit ripen in late August to September. Unfortunately the plant does have thorns.

There is very limited 2014 availability from Henry Field's Nursery that is selling the plant under the name 'Sweet Repeat'. Plants of Niwot won't be widely available until 2015 from Nourse Farms, Inc.

Spring garden transplants

Front Range gardeners most commonly associate transplants with warm season vegetables such as tomatoes planted the end of May. Transplants are also useful in the spring, cool season garden for many of the same reasons.

The mid-March to mid-May period of cool spring weather is short. Planting out transplants as soon as soil and air temperatures allow enables you to mature crops before weather warms in May. This extends your cool season and maintains quality.

One family of plants best transplanted rather than direct seeded into the spring garden is the Brassicas or cabbage family. If broccoli and cabbage plants are large enough and exposed to several weeks of cold (under 50 degrees), they will produce flower stalks.

It is better to start broccoli and cabbage transplants in warmth indoors and plant them outside in mid-April when sustained periods of cold weather are less likely but temperatures are still "cool". It is a tricky concept to grasp.

Broccoli generally does well for gardeners here and if you have never grown it, the superior flavor far exceeds supermarket purchased heads. Early to mid-March is the time to plant seed to grow a 4 to 5 week old transplant ready for early to mid-April planting in the garden.

The photo shows seed of the Burpee broccoli variety 'Sun King' seeded to grow transplants. It's a 71 day variety new in 2013 that is advertised as having unrivaled heat tolerance, a useful trait in our area where warm days can come early. Did anyone living in Colorado's Front Range try it last year and what were your results?

Cabbage likewise grows well here and can be transplanted in the same manner. Cauliflower is much more sensitive to any cultural factor (temperature changes, moisture fluctuations, fertility, insect attack) and is a challenge to grow. Brussels sprouts are longer season plants best planted mid-summer for fall harvest on the Front Range. The spring cool period generally isn't long enough to grow them before hot weather sets in.

Note that most of the Brassica crops are perhaps easier grown as fall rather than spring crops on the Front Range. However they are worthwhile planting in your spring garden as well as later for fall crops.

Photo credit: Seeded broccoli transplants - Carl Wilson

Time to plant hardiest seeds

The hardiest seeds (lettuce, onions and parsnips) can be planted out now that soil temperatures have reached 35 degrees F on the Front Range. Soil temperatures at the online Ft. Collins soil temperature website have been bouncing around between 36 and 39 degrees F since the beginning of the month. Soil temperatures warm on sunny, 50 to 60 degree days and cool in cloudy/snowy weather.

Parsnip seed is notoriously slow to germinate. It may work well to plant them with radishes to gain double use from the area. Quick maturing radishes can be harvested in 20 to 30 days and parsnips require the whole season (100 to 120 days depending on variety). 'Hollow Crown' is an heirloom variety (heirlooms are open pollinated varieties that have been in cultivation 50 years or longer). Other parsnip varieties are 'Lancer', 'Albion' and 'Javelin'.

Planting now means soil should have been fall prepped. Last season's dead plants should have been carted away or composted and the soil tilled and left rough to further break up during winter freeze-thaw. Any compost should have been added then. Note if you grew a winter cover crop, it will require 30 days after tilling under before you can plant vegetables.

Other spring crops require a 40 degree F soil temperature for seed to germinate. These include spinach, kale, beets, carrots, peas and more. Hold off on planting them for now. Of course if you have a soil thermometer and have reached forty at your Front Range Colorado location, proceed with planting.

Photo credit: Parsnip and Lettuce seed packets - Carl Wilson

Learning from the 2013 Gardening Season

The 2013 gardening season was bookended by a very hard freeze on May 1st (19 degrees F in Denver) and a week of rain starting September 9th that soaked gardens and caused record flooding along the Colorado Front Range and plains. The last spring freeze in Denver was May 5th (our average date) and first fall freeze October 4th (October 7th is average date).

Gardeners who planted cool season crops in mid-March achieved a harvest before the May 1st hard freeze although bolting afterwards was an issue. Eighty degree temperatures arrived the last week of May (85 degrees F on May 26) that prompted decline of cool season crops.

For planting warm season crops forty degree lows continued through the end of May and consistent fifty degree F or above nights didn't arrive until June 9th. One 92 degree F day occurred June 3 and then a record 99 degrees F June 10th and 100 degrees F June 11th. Early planting of very warm season crops such as tomato or peppers was best delayed until June or done with water walls if planted earlier.

Vegetable gardeners who haven't considered temperature moderating devices such as water walls until now may want to rethink their approach. It is generally accepted that temperature swings will be more pronounced with worldwide climate change. Take advantage of mulches and season extending devices if you haven't already to achieve satisfactory harvests.

Keep on planting

Follow-on crops to those spring and quick maturing crops already harvested from the garden are the order of late June. Don't let recent above average temperatures in the mid to upper nineties F deter you. If you use hot weather seed germination techniques, summer direct seeding in the garden isn't hard.

Carrot seedlings germinated under
polyester floating row cover fabric.

I recently germinated notoriously slow-to-germinate carrots under germination fabric. This is the same material that many people call floating row cover fabric, simply used for a different purpose. It is readily available in garden centers and will last for many seasons.

Plant seed shallowly as normal, cover bed with cloth, bury edges with soil and/or use bent wire U pins punched through fabric to hold down the middle from winds. Water frequently but in small amounts right through the fabric. Remove fabric upon germination. My carrot seed germinated in 10 days.

If you are interested in more follow-on gardening techniques for late summer and fall growing, join me for my July 10 class at Denver Botanic Gardens (see class list at right).

Photo credit: Carrot seed and Carrot seedlings under row cover fabric - both Carl Wilson

Weather Changes to Too Hot

In typical high altitude fashion the weather has gone from too cold nights to too hot days for vegetable crops along the Front Range of Colorado. A new record high of 99 degrees F was reached in Denver on June 10 and more temperatures in the nineties are expected to follow the rest of the week.

Lettuce now bolting

Tomatoes will stop growth at temperatures over 95 degrees F. These hot days have arrived just when we have plants established and want them to grow vegetatively to develop a good sized frame to set blossoms. Moderate temperatures between 65 and 85 degrees F are best for tomatoes and the last few weeks illustrate why the Front Range is less than ideal for growing them.

The cool season crops will quickly wane with hot weather. Spinach bolts and goes to seed at high temperatures especially under long days. High temperatures cause lettuce seedstalks to develop and quality to decline quickly as this photo taken a few days ago shows. 

'Indian Red Giant' mustard starting to bolt  -
 photo taken two days before post

Several of the oriental brassicas have a tendency to bolt under the following conditions. Low temperature in the early stage of growth is thought to be the single most important factor. If seedlings log enough heat units before the low temperatures, bolting is prevented. The long days of June are another risk factor. Stresses such as transplant shock, lack of or excess water, and temperature shocks increase bolting risks.

Once bolting begins, salvage leaves immediately before quality declines further. Choose bolt resistant varieties next time or use bolt-prone varieties as cut-and-come-again seedling crops to avoid the bolting issue.

Low humidity and drying winds of 10 to 30 mph this week will make conditions difficult for young vegetable plants and seed germination in progress. Frequent, light waterings and wind protection if available are in order.

Photo credit: Lettuce bolting and 'Indian Red Giant' mustard bolting - both Carl Wilson