Anchorage Daily News

It may be dirty business, but a good garden starts with the soil. With Anchorage's traditional planting date, Memorial Day weekend, looming on the horizon, it's time to prepare your soil.

Garden books and magazines stress the importance of not working the soil when it's wet. This is especially true of heavier soils containing clay and high amounts of silt. Fortunately, many Anchorage gardeners have sandy loams that are not as prone to compaction. Tilling or digging a heavy soil with too much moisture leads to long-term problems. It creates clods that, once dry, have the strength of concrete and are almost impossible to break apart.

Once the soil has dried out properly, you can speed up the warming process by covering it with a sheet of clear plastic. If you're gardening in raised beds, staple the plastic to the sides of your boxes to keep it from blowing away. The real fun is watching how quickly a few sunny days will raise the soil temperature by 10 degrees. It's well worth investing in a soil thermometer so you can see the results of your actions.

Once your soil is warm, if air temperatures cooperate, you may be able to plant a week or two earlier. There's no rule that says the entire garden must be planted at once. Seeds and cool-season transplants such as broccoli, cabbage, pansies and snapdragons can handle cool temperatures if they are properly hardened off.

But before you start putting plants in the ground, there are a few other steps to getting your soil ready. Do you really need to rent a rototiller or turn the soil over with a shovel? With all the talk about sustainable gardening and Earth-friendly growing techniques, no-till agriculture is a method that a number of gardeners are considering. Raised-bed gardening has many advantages, my favorite being that you don't have to bend down so far. But another beauty of the system is that you don't walk in the beds and compact the soil. So theoretically, you shouldn't have to turn the soil and disrupt the natural cycle of the microorganisms that live there. However, if you have birch or spruce anywhere in the vicinity, their roots will have found their way into your beds where there is easy access to the water and nutrients you are supplying to your flowers and vegetables. If you don't sever these roots, your garden will suffer.

The other benefit to turning over the soil is that it allows you to work soil amendments into the root zone. Weed-seed-free compost, fertilizer and lime can all be spread on the surface before you start digging. How much you should add is difficult to say.

Most vegetables and flowers will grow well if soil pH is between 6.0 and 7.0. If you've been liming regularly, you may not need to do so again this season. Not only is lime expensive, but once you raise the pH of your soil too high, it negatively affects a plant's ability to take up nutrients. Many greenhouses will do a pH test as a public service. Home test kits and pH meters are also available.

The standard soil test performed by the Agricultural & Forestry Experiment Station in Palmer costs $40 and includes pH, nitrogen, phosphorus, potassium, lime and fertilizer recommendations. You can pick up a test packet at UAF Cooperative Extension Service offices. In Anchorage the location is 2221 E. Northern Lights Blvd., behind Medical Park. The packet includes a bag for mailing soil to the lab along with your check. It will take at least two weeks to get your results. If you're ready to prepare your soil now, I'd suggest waiting until fall if you wish to submit a sample.

Peter Bierman, land resources agent with the University of Alaska Anchorage Cooperative Extension Service in Palmer, has written a new publication titled "Factors to Consider in Selecting a Soil Testing Laboratory." For a free copy, contact the UAF Cooperative Extension Service at 786-6300 or download it from the CES Web site, www.uaf.edu/ces/publications/anrpubs.html#fgv.

Soil can also be tested for microorganisms including bacteria, fungi and protozoa. This type of testing costs more than $100 and is performed by labs outside Alaska. Microorganism populations in the soil are very sensitive to temperature and moisture conditions. According to Dr. Jeff Smeenk, Cooperative Extension's commercial horticulture specialist, you can jump-start microbial numbers by adding well-cured compost, worm compost or aerobic compost tea. But just maintaining a healthy garden also increases microbial activity. Plant roots leak food that microorganisms love. This leads to an increase in numbers and a breakdown of organic materials, which in turn helps plants to grow. It's a wonderful biological circle.

Many references suggest adding peat to garden soil. Anchorage gardeners who have purchased topsoil are likely to already have a soil with a high peat content. Peat is quite stable and is not considered to be an active source of organic matter from which microorganisms can release nutrients. Peat does affect a soil's water-holding ability.

If you've brought in new topsoil, chances are good that the pH will be low (acidic) and the soil will need to be limed to facilitate proper plant growth. The amount of lime you need to add varies depending on soil chemistry and texture. It takes more lime to change the pH of a soil that is claylike or has a high organic matter content than it does a sandy soil with little organic matter. The Anchorage UAF Cooperative Extension Service can provide you with a liming chart based on average garden soils for this area.

Most new topsoil is also low in the primary nutrients, nitrogen, phosphorus and potassium. The same holds true for native soils that have never been gardened. These nutrients are easily applied by adding fertilizer. A common recommendation is to add 3 to 4 pounds of 8-32-16 or 10-10-10 per 100 square feet of garden, or 2 to 3 pounds if you're making a new flower bed. Organic nutrients can also be added in the form of fish meal, cottonseed meal, bone meal and green sand, to name a few. Unlike most organic fertilizers, blood meal can burn plant roots. Make sure to mix it well into the soil before planting.

It makes sense to spread out any lime, fertilizer or other soil amendments you intend to use before you turn over the soil. This way, you only have to till or dig the soil once.

Once summer is under way, tune in to the color and growth of your plants. Lower yellow leaves indicate low nitrogen levels. A purpling signals phosphorus deficiency. This is easy to see on the undersides of young tomato leaves or on newly transplanted marigolds. Sometimes phosphorus is present in the soil. It may just be too cold for plants to take it up.

Soil preparation doesn't have to be a big mystery. Keep it simple. Apply compost, organic matter and fertilizer. Don't overdo the lime. Don't plant if the soil is too cold. Watch the growth of your plants and add additional fertilizer during the summer if plants seem to need it.

Julie Riley is horticulture agent with the University of Alaska Fairbanks Cooperative Extension Service in Anchorage.