Greens crop replacement

Buckwheat seedlings following
harvest of spring lettuce crop

The onset of ninety degree F weather along the Front Range means those cool season greens that have lasted so long this year due to a cool May will soon be gone. The heat decreases quality (bitterness), long days induce bolting, and the crops days to harvest may have just ticked by.

What to do now? In late June to mid-July you can begin planting mid-season crops for late summer or fall harvest. Some crops tolerate heat well such as Swiss chard, bush beans and New Zealand spinach. Collards can be planted up to 3 months before frost by direct seeding. Root crops that mature in 50 days such as beets and carrots are also good bets.

With other vegetables it is best to chose heat tolerant varieties. With lettuce the Cos (Romaine) types as well as others noted for heat tolerance (such as 'Muir' cultivar Batavian type lettuce) can work. Note that lettuce seed has a natural thermal dormancy and seed may not germinate well at high temperatures. Pre-germinate seed, plant in cooler weather and use irrigation to cool soils to obtain germination.

Likewise with spinach look for heat tolerance such as in the Asian arrowhead types; one example is 'Flamingo' cultivar.

Keep in mind crop rotation when second cropping, rotating to a crop from a different plant family. In addition to edible crops, remember you can also utilize a summer green manure (soil building) cover crop such as buckwheat, Fagopyrum esculentum. Turn under in 30 to 40 days as it starts to flower to increase soil organic matter.

Photo credit: Buckwheat seedlings - Carl Wilson

Seed or transplant for Fall

Now is the time to finish seeding or transplanting 50 to 60 day crops to mature in Fall. We just finished installing kale, red and golden beet transplants (photos). Even though it's hot now, these crops and others including lettuce will grow and be of good quality as they mature in cooler fall temperatures.

Planting a second crop where spring crops leave "vacancies" increase yields from a given square footage of soil during a growing season. Rotate crops and don't plant same family plants such as kale following cabbage. We planted beets following lettuce and cabbage, and kale following beets.

This higher demand on garden soil is equivalent of a full season crop such as tomato or potato. It requires adequate organic matter and fertility to meet the needs of the second crop so do be sure your soil is prepared to handle succession planting.

Photo credit: Transplanted kale, red beet, golden beet - all Carl Wilson

It’s time to seed fall vegetables

Although it may seem that vegetable gardens have just begun growing well and planting is done, it’s time to seed crops for fall harvest. Sixty day crops planted in July will mature in September as weather is cooling.

Look at seed packets and note the days to harvest. Count back from the first fall frost date, October 11 for the Denver area. With cool season vegetables note that many tolerate the first light frosts of fall very well and an extended harvest period can be expected. Warm season vegetables must be planted to mature well before frost when temperatures remain warm.

Here are some vegetable planting suggestions listed with their typical days to harvest. Cool season vegetables such as peas (65), cabbage (85), collards (55), broccoli (65), kale (60), spinach (40), lettuce (60) and endive (45) are good candidates. Root vegetables such as beets (60), carrots (70) and turnips (50) can be planted this month. Even some fruiting vegetables such as bush beans (60) and cucumbers (55) can still be planted if done by mid-July. The very short season radish (30) can be planted into August with success.

Note that peas planted for fall harvest (photo above) are prone to powdery mildew. Choose powdery mildew resistant varieties. Be sure to provide support such as netting stapled on posts (right) for them to climb to insure good air circulation. Often harvests are reduced as compared to spring plantings. I’m willing to gamble on these Oregon Sugar Pod II’s because I like snowpeas and have a separate area where the air movement is not blocked by tomatoes or other vegetables.

Planting fall crops in “succession” where other spring crops have been harvested is a way to extend harvests past the first frosts and maximize yields from your garden.

Photo credit planted pea seeds and pea netting - 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