Soil Preparation for Root Crops

by National Gardening Association Editors

This part of gardening is the key to healthy root crops - you need to prepare a foundation for your plants just as you would for a house. If your foundation is weak, your house falls down. Your plants can fail, too, but you won't have to worry if you get your soil into good shape before you plant. Here's the formula for success:

First . . . pH

You should check the pH of your garden soil at least every couple of years. The most accurate reading is taken in the fall. pH is the measure of soil acidity or alkalinity, with 7 indicating neutral on a scale from 1.0 (most acid) to 14.0 (most alkaline). Root crops and most vegetables prefer slightly acid soil, with a pH of 6.0 to 6.8.

To test your soil pH, you can buy an inexpensive testing kit at a garden center, or send a soil sample to your County Extension office if it offers that service. The test may indicate that you need to add lime to raise your pH or sulfur to lower it. Just follow the recommendations accompanying the test results.

The Wonders of Organic Matter

Root crops are harvested for what grows down, not up, so they really need the best possible growing quarters - preferably soil that is loose, rich and loamy.

To achieve this ideal soil condition, work into the soil plenty of organic matter such as leaves, compost, grass clippings, garden residues or easy-to-grow cover crops like buckwheat, cowpeas or annual ryegrass.

Most of us have less than perfect soil, ranging from light, sandy soil that drains too quickly all the way to heavy clay soils that take forever to drain and warm up in the spring. Whether you work on a garden-wide basis or just improve the spot where your root crops will be, here's how adding organic matter to the soil will help:

Organic matter feeds the soil life that will in turn break it down into nutrient-rich humus. In sandy soil that doesn't hold moisture, organic matter will make the soil act like a sponge, holding moisture to nourish the expanding taproots. On the other hand, with a heavy soil that doesn't drain well, the particles of organic matter wedge themselves between the tight soil particles so that air and water can circulate better.

A word of caution about adding manure to your soil: try to get dehydrated or well-composted manure, because even aged manure contains some weed seeds. By spreading it over your garden, you may be planting extra weeds, and that just doesn't make sense! The heat process of dehydrating or thorough composting kills most of the weed seeds. If you can't get well-aged manure, use what you have, but stay on the lookout for weeds.


Root crops taste better if they grow at a steady pace, and they need certain nutrients for this smooth growth. These nutrients are available in commercial fertilizers, which you can broadcast over the planting area and mix into the top two to three inches of soil.

The best time to add fertilizer is on planting day. If you wait more than a few days between fertilizing and planting, some fertilizer is bound to leach away or lose its potency.

Apply two to three pounds of a balanced fertilizer such as 5-10-10 for each 100 square feet. The numbers 5-10-10 or 10-10-10 refer to the percentages by weight of nitrogen (N), phosphorus (P) and potassium (K) in the bag of fertilizer, and they're always listed in the same order: N-P-K.

These three major plant nutrients are essential for proper plant growth. Nitrogen aids in leaf and stem production, phosphorus promotes strong roots and potassium also helps in root development by conditioning the entire plant.

Seeds are sensitive, and they can get burned by the nitrogen in any fertilizer that touches them. By mixing the fertilizer thoroughly into the soil, you can prevent that kind of accident.

The easiest way to avoid fertilizing mistakes is to always mix the fertilizer completely into the soil, and with root crops, to go easy rather than overdo it. Don't be tempted to add that extra handful of fertilizer. You may end up with no carrots at all - just lots of bushy tops!

You can aid root growth, however, by adding a little extra phosphorus in the form of bonemeal or superphosphate (0-20-0). Sprinkle it directly onto the rows just before planting the seeds, raking the bonemeal into the top inch of soil so it can be used by the young seedlings when they come up. A handful is about right for every four to six square feet.

Phosphorus won't burn the seeds, but the plants will only use as much as they need. So don't overdo it because excess will just go to waste.

You can also work a light coating of wood ashes into your soil before planting to ward off root maggots. Wood ashes can raise the soil pH because they are very alkaline, so don't overdo it. As with lime, the best time to add ashes is in the fall, but they may be added in the spring - they just won't have as much time to work. The right amount is four to five pounds per 100 square feet, mixed into the top two to three inches of soil.

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