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How to grow a garden: Three important factors to consider before you plant

Not all dirt is created equal

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Marie Viljoen's first terrace in Brooklyn measured just 66 square feet, yet she managed to turn the tight space into an outdoor oasis with a small grill, a table and chairs, and dozens of plants: roses, herbs, figs, lilies, strawberries, vines, and more. Her micro garden grew into a blog and a book, both named after the tiny terrace’s size. Here, Viljoen shares her expertise for a successful garden.

Your outdoor space is ready, you have your ideal landscape sketched out, and you want to start planting. But hold your horticultural horses until you have considered three important factors if you want to save yourself some flora-induced stress and money in plant-replacement.

Know the dirt on your dirt

The soil is where it all begins—or ends.

If you are gardening in-ground, you have to work with the earthy hand that you have been dealt. What is in your soil? For starters, in a city, two words: heavy metals. Don’t freak out.

The highest risk of heavy metal poisoning is for toddlers and small children who play outside and inadvertently ingest dust and soil. Secondly, the concern is for gardeners who grow edible plants.

In terms of lead, it is the residue or soil on the outside of the plant that is the problem. This is solved by thorough washing. As it turns out, most plants—there are exceptions, like ferns—do not absorb enough lead to hurt an adult. Root crops will absorb most (which accumulates largely in their skins), followed by leafy greens, with fruit absorbing the least, if any. Also, acidic soils (with a low pH) make lead available to plants. Sweetening the soil—raising the pH to near-neutral (which is seven)—by adding soil amendments like garden lime or ground oyster shells, makes lead unavailable for absorption.

Arsenic and cadmium are more serious.

What to do? Before you plant, contact a local university or lab, take the recommended samples, and send the package for analysis. Apart from heavy metals, the analysis will reveal your soil’s pH, which will guide you in choosing the best plants for that environment, what nutrients are in the soil, and the quality of the soil. There will be recommendations for correcting any problems.

What if the soil test comes back for heavy metals well above the recommended levels for your state? It depends what they are. Lead can be managed, as mentioned above. But arsenic and cadmium, for example, are non-negotiable. Replacing soil in a garden is very costly. If you still want to grow edibles, your next step is to build raised beds or to use planters. These will be filled with bagged potting soil.

Potting soil is a pricey purchase, but you only do it once if you're gardening in containers. You are starting with a clean slate, and no in-ground contaminants.

Avoid anything labeled “topsoil.” Topsoil is too heavy. You want a potting medium, often labeled potting soil, despite the fact that there will be very little, if any, actual soil in the bag. It is much lighter.

Good potting media are a mixture of products like compost, manure, guano, worm castings, seaweed, coir, bark, and perlite. The bag will list the ingredients. Of course, you want to grow organically and sustainably (don’t you?). Counterintuitively, the business of gardening is very tough on the planet. As a general guideline, avoid bagged mixes that contain peatmoss and synthetic fertilizers; the harvest and production of both is environmentally problematic. Some brands carry organic products while the bulk of their business remains conventional; I personally avoid Scott’s Miracle Gro, a Monsanto partner. Do research and find out who owns the bag you want to buy.

How much potting soil will you need? Calculate the cubic feet (volume) of your containers by multiplying each one’s length by width by depth. A 3 x 1.5 x 1.5-foot planter will have a volume of 6.75 cubic feet. Most potting mixes come in a handy cubic-foot size. You’d need six bags, taking into account that your plants’ root balls will use up some volume.

Learn how to plant properly

So the soil is sorted, and you have your plants, which were carefully chosen to fit your USDA Hardiness Zone and sun exposure. Plants purchased in grow-pots from a nursery must be wiggled gently free of their container. With your fingers, loosen the root and soil mass that emerges. If the plant is rootbound with a rigid white root mass, use the blade of shears or a small garden fork to slash the roots from top to bottom. This helps rather than hurts; new feeder roots will establish to absorb soil nutrients and water.

Place the plant in a hole the same size as the root mass. Add soil to fill in and tamp down firmly. Soil will settle with watering. The top of the plants’ root and soil mass must be level with the surrounding soil (too low and water will pool, causing rot; too high and the roots will dry out).

If you have bought a bare-root plant, soak it in a basin of water before planting. Make its hole as deep as the roots are long. Water at once.

Be prepared to water adequately and regularly

A thorough soaking trumps a sprinkle. In pots, water till moisture seeps from the drainage holes. And there must be drainage holes. When to water next? Most new gardeners overwater. If the soil looks dark and feels damp, like a wrung-out sponge, no water is necessary. If the soil is paler, and is dry to an inch deep (stick your finger in), soak it. Smaller pots will dry out faster. To cut down a little on watering duties, add a hydrogel like Terra-Sorb to the soil mix when planting.

Soaker hoses on a cheap timer can save you for a weekend away from the garden. And if you have the budget for professionally installed automatic irrigation (which will run into several thousand dollars), go for it. But the settings will still have to be adjusted through the growing season.

Finally, for the best outcome, visit the garden every day. Observation and time are the best teachers.