Wednesday, March 24, 2010

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

Saturday, March 13, 2010

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

Tuesday, March 9, 2010

Late dormant season fruit tree pruning

Before buds break in March, prune dormant fruit trees. Recently I helped prune peaches in a Denver community garden (unpruned peach photo left). Peaches must be pruned hard every year as they only bear fruit on one year old twigs. Renew them yearly by pruning to replace nearly all fruiting wood. Two year old or older twigs are unproductive.

The photo left illustrates how hard this pruning should be on peaches (pruned branch left, unpruned tree right side of photo). You should end up with a skeleton of thick, blunt scaffold limbs sprouting very few thin, one year old twigs (photo right). Leave bearing twigs of 12 to 18 inches in length removing the shorter ones (bear small fruit) and longer ones (bear too many and are subject to breakage).

Twigs pointing upward and out at 45 degree angles from horizontal are most productive. Remove vertical and downward pointing twigs. “Stacked” twigs or branches growing over top one another shade the lower twig so remove one of them.

Prune trees to allow light into the center of the tree. With fruit trees, light equals fruit. Dense, unpruned trees will yield poorly. Remove dead and interfering branches, renew fruiting wood, and control size to keep bearing wood close to the ground.

Maintain a zone of equilibrium between excess growth (the rank growth tendency of the top of the tree) and poor fruiting (lower portion tendency). Do this by pruning harder in upper, outer portions of a tree to allow light in. Most home gardeners tend to prune mature trees too little.

Finally, remember that pears, cherries, apricots and most apples bear fruit on short spurs that last for some years. This is very different than peaches so don’t prune off the short spurs or you will have no crop.

Here’s hoping that spring freezes spare our fruit tree blossoms so we can have a good fruit crop this year.

Photo credit, All peach pruning photos, Carl Wilson

Wednesday, March 3, 2010

Vegetable Gardening 101 class

Learn the keys to successful vegetable growing on the Front Range including tips and tricks to make your gardening life easier. Colorado’s climate realities include a short growing season, cool summer nights, dry air, erratic late spring and early fall frosts. Soil conditions add another gardening challenge. The guiding hand of you, the grower, makes all the difference in altering growing conditions to achieve results. Come learn when and how to intervene to produce the vegetables you want for fresh eating and preserving.

Instructor: Carl Wilson

For: Beginning to intermediate gardeners

Dates: Saturday, March 20, 2:30 to 4:30 p.m.
repeated Saturday, April 10 same times

Location: 200 Santa Fe Dr., Denver

Click to Register: Denver Urban Homesteading
Cost: $25

Photo credit: Plant starting under lights, Carl Wilson