Saturday, June 29, 2013

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

Tuesday, June 11, 2013

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

Saturday, June 1, 2013

Tough Weather Week for Vegetables

This past week was a tough one in Front Range vegetable gardens from several standpoints. For establishing tomatoes, we had five nights of overnight low temperatures in the forties F with a sixth night predicted tonight. The official early morning low on June 1 was 42 degrees F. [Postscript - the sixth night June 2 low was 39 degrees F - brrrr!]. This long stretch of lows under fifty degrees F will stop growth of tomatoes and take more days for growth to resume once lows are again in the fifties the first week of June. Can you say lost days for your tomato growing season?

Tomato transplants held for June planting 
Of course if you have your plants in nighttime heating water walls this has not been a problem. The other option some people have taken is keeping their plants "on the shuttle", bringing potted transplants in at night and setting them outdoors by day. June 2 will be the day to plant for those who have waited as this will be the first nighttime low over fifty F. If you timed growing transplants not to become too large, you will have success with holding as plants have stayed in active growth mode.

Remember tomato transplants can be planted deeper than they were growing in the pots and will root out along the stem. This only works if you have a deep depth of decent soil or use the horizontal-planting-with-upturned-top method in shallower topsoil.

Chances are very high the last spring freeze will have passed at this point. Remember the average last freeze in Denver is May 5 with the latest freeze occurring June 8, 2007. For kicks I'll throw in that the latest date of the last measurable snow in Denver was June 12, 1947 (data from NOAA National Weather Service Denver/Boulder office).

The second reason this was a tough week for vegetables was several days of winds in the twenty to thirty mph range. This dried foliage of newly established transplants or germinated seedlings. Careful watering and setting up wind protection structures were in order.

Photo credit: Tomato transplants held for June planting - Carl Wilson