Transplant growing

Transplants being produced for setting out in mid to late May should be well along by now. The peppers in the photo are being grown for sale at our Plant-A-Palooza fundraiser. They are the improved chile types described in the recent “Back to the Future” article about chile seed that was cleaned up to be the more productive and flavorful peppers they used to be. Information on the sale is in the top right corner of the blog.

It’s been hard with recent cold/warm weather punctuated by rain/snow to move transplants outdoors during the day for a dose of sunshine. Even when day temperatures have been above 55 degrees F for peppers and tomatoes, it’s often been excessively windy. While mild wind is fine for promoting strong stems, gales are not.

Shuttle homegrown transplants outdoors on warm, calm days and bring them in before temperatures cool too much in late afternoon. This acclimates plants to drier air and UV light, helps build thicker stems with flexing from wind movement, and provides higher light intensity than generally available indoors. Leave plants indoors when air temperatures are in the low 50’s or below. Of course transplants of cabbage and other cool season crops will withstand cooler temperatures. Many of these should have been set out and already out of the house.

Do balance light and temperature to promote growth with adequate fertilization for good plant color. Avoid excessive fertilization which produces lanky, succulent growth. Watch for golden yellow lower leaves that indicates the need for nitrogen fertilizer and for purpling suggesting the need for phosphorous (photo left).

Between timing seed planting to have the plant the right size to set out, manipulating the environmental light and temperature conditions, and regulating fertilizer nutrients, growing transplants is an art as well as a science.

Photo credit: Chile pepper transplants, Phosphorous deficient tomato - both Carl Wilson

Winds don’t defeat seed germination efforts -

Wind, wind go away! If you regularly check this blog you might have gathered by now that I’m a big fan of germination fabric. With all the recent windy days, I thought the lettuce, kale, kohlrabi and other small seed I planted might not germinate. It seemed like the surface soil was drying out faster than I could replace it with once or twice a day watering.

Indeed I wasn’t sure the fabric would stay in Colorado and not end up in Kansas. This in spite of being secured with wire U pin anchors punched through the fabric into the soil plus heaps of soil piled on the edges. I got good germination, thank you, as you can see from the photos of lettuce seedlings left and the familiar notched leaves of cabbage family plants right. I know I couldn’t have achieved that germination percentage if it weren’t for the fabric.

Shallow planting to avoid burying seed and surface moisture for germination (wetting top ¼ to ½ inch) are critical to getting seedling emergence.

The next challenge is to keep seedlings moist enough to develop a root system and grow. After that they can be weaned from light, frequent watering to less time intensive every two day and then every three day watering. Gradual changes in watering frequency are best to avoid stressing plants. Keep them actively growing to preserve quality.

Photo credit: Lettuce seedlings and kohlrabi seedlings, both Carl Wilson

Seed warm season crops indoors now

It’s now 7 weeks out from the May 31 traditional Memorial Day transplanting date for warm season crops into the garden. Even though the Denver last frost date is approximately May 10, many gardeners wait until the end of May when weather is more stable to set out tomatoes, peppers, eggplant, squash and more.

If you plan to grow your own transplants, 6 weeks before transplanting is generally sufficient for tomatoes and 8 weeks for peppers. Have the soil in pots warm (70 to 75 degrees F is ideal) and grow in a warm room, not cold basement. One advantage we have in Colorado is many days of bright sunshine so growing in a sunny window is doable even without a greenhouse.

A guide for seeding and transplanting vegetables into the garden based on outdoor soil temperatures follows (see last week for soil temperature details and on-line soil temperature readings link):

Garden soil temperature and planting times
35 degrees F – lettuce and onions
40 degrees F - peas, radish, spinach, cabbage
50 degrees F – tomato, pepper, corn
55 degrees F – beans
60 degrees F – cucumbers, squash, eggplant

Photo credit: Peppers seeded and growing in window - Carl Wilson

Time to seed early vegetables

A check of soil temperatures today showed 41 degrees F. That’s warm enough to seed cool season crops such as lettuce, onions, peas, radishes, spinach, cabbage, broccoli and kale in an open garden. (Those using coldframes could beat this planting date by a month or more.)

Soil temperatures should be measured at 4 inches deep at 8:00 a.m. If you don’t have a soil thermometer, you can follow the on-line readings taken at the weather station on the Fort Collins campus of Colorado State University.

Once seeded, you may want to cover with a germination blanket (photo above) to keep small seeds moist until seedlings emerge and even for a week or so afterwards. Our sun, wind and dry air at mile high elevation rapidly dry the surface of soil. This material, anchored with soil at the edges or U pins of bent wire punched through the fabric, helps the surface stay moist. It’s sold as floating row cover or seed germinating fabric at garden centers.

Even with a fabric cover and cool temperatures, at least daily watering likely will be necessary during the days to germination period generally listed on the seed package. In addition to proper planting depth (avoid seed burial deeper than recommended), maintaining consistent moisture is the biggest factor in successful seed germination.

Photo credit: Using seed germination blanket, Carl Wilson

Hold your spring soil prep enthusiasm

If you didn’t prepare soil in the early part of March when it was dry, think twice about when to do it now. Two snowstorms on the 19th and 23rd (see raised bed photo right) each left my Denver garden with an inch of water, 2 inches total in less than a week. Heavy, spring snows can bring a lot of welcome moisture to gardens when snow melts (photo below left) but can interfere with cultivating soil.

Clay soils are especially sensitive to tilling at improper moisture content. They should be tilled at medium moisture, not too wet and not too dry. Tilling when too wet can create clods that take years to disperse on some clay soil types.

To check moisture, take a handful of soil and gently squeeze into a ball. If the ball crumbles when poked with a finger, it can be tilled. If the ball only reshapes with the pressure of poking, it’s too wet. Wait for it to dry more. With some clay soils there may be only a few days when soil is at the proper moisture content. If spring snows or rain are frequent, planting may be delayed.

Very wet soils are also easily compacted. Stay out of the garden when soil is wet. Water acts as a lubricant allowing soil particles to more easily slide over each other. Don’t compact soil that you worked so hard to make loose by walking in a wet garden.

One other moisture related matter is worth mentioning. Wet soils warm more slowly because the sun’s energy is used in evaporating water rather than in raising soil temperature. Cold soils will delay planting further.

Photo credit: Snowy spring raised bed gardens, both Carl Wilson

Turn under winter cover crops

If a winter cover crop of rye or Austrian winter pea was planted in the fall, turn it under a month before planting or seeding. I turned my winter rye under this past weekend adding “green manure” to the soil.

The large soil critters such as the earthworm pictured here (below right) and soil microorganisms will “chew” through the raw roots and tops over the next weeks for soil improvement. I left the soil “rough” and certainly didn’t step on and compact it. That’s an advantage of raised bed gardening – standing outside the bed to work your soil. It will not be tilled again when seeding or planting so the soil structure can be preserved as much as possible. More tilling would simply destroy it and there is no good reason for it.
















First, why do you need to wait a month before planting? The living critters working over the plants consume soil oxygen and can create plant health problems if not tilled in ahead of time. Once the bulk of the “raw” plants have been consumed, the soil environment stabilizes and lack of oxygen for plant root growth is no longer a problem.

Second, it’s about more than the buried plants. If it was only the plants we could find a way to chop them into fine pieces and instantly improve the soil. The secret is what the soil critters add to the mix and the squeamish need read no further. Simply know that without them, you couldn’t realize the soil structure and fertility improvement benefits from planting and turning under cover crops.

Large and small critters feed on the buried plants adding substances such as slime, mucus and fungal mycelia. Analyzing these substances show things such as gums, waxes and resins which glue soil particles together. Clumped particles enhance the tilth, porosity, and water holding capabilities of soil – all good things for healthy plant growth.

Take care of your vegetable garden soil and it will take care of you.


Photo credit: Two soil spading photos - Carl Wilson