| Sawdust can be used as mulch and is often recommended around blueberries and other plants that prefer an acid soil. It is best if the sawdust has been composted for at least six months (preferably one year). If not, it can tie up available nitrogen in the soil and create a deficiency in the plants growing there. You can also add pound of actual nitrogen per cubic yard of sawdust to avoid the problem. Very fine sawdust can pack down and interfere with the movement of water and air through the soil. Be sure to stir it up periodically to avoid this problem. A 2- or 3-inch layer is sufficient to help keep weeds down, maintain soil moisture and moderate soil temperatures. Avoid piling it up around the stems of plants, especially if it has not been composted thoroughly. For example, 10-10-10 is 10 percent nitrogen, 10 percent phosphorus and 10 percent potash, always in that order. 0.5 divided by 0.1 equals 5 pounds of 10-10-10 fertilizer added to a cubic yard of sawdust. It is helpful to choose a fertilizer that contains only nitrogen, such as urea (46-0-0). It will take about 1 pound of urea to add one-half pound of nitrogen. Q. I have noticed a yellowish-white crust on the surface of the soil and sides of my clay pots on many of my houseplants. Is this some kind of fungus? What you are seeing is the accumulation of soluble salts from fertilizers and the minerals dissolved in hard water. Fertilizers are salts, just like table salt, except that they contain plant nutrients. As the salt builds up in the soil, it becomes difficult for the plants to take up water. To minimize this buildup, be sure to water houseplants until the water comes out of the drainage hole(s) every time you water. It is easiest to put smaller pots in the sink or bathtub and water them there. Use a turkey baster to empty the saucers of plants too large to move so they do not sit in the drainage water. Otherwise, the soluble salts will be reabsorbed as the soil takes up
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