Some folks in my part of New England plant seeds in the ground on Mother’s Day and seedlings on Memorial Day weekend. Not me. Soil temperature is the only true sign that the time is right to start planting.
Some folks in my part of New England plant seeds in the ground on Mother’s Day and seedlings on Memorial Day weekend. Not me. Others use Mother Nature’s clues: plant spinach when the forsythia blooms, potatoes when the leaves of an oak are the size of a mouse’s ear. That sounds good, but who really knows how big a mouse’s ear is?
I start a lot of seedlings indoors, some as early as February, and (like any good mother) I am protective of my young. I only put out plants or plant seeds when I am sure that they will succeed.
So I plant my tomatoes and other heat-loving plants in June, generally after the 10th of the month. Those heat lovers include tomatoes, peppers, eggplants and all the vine crops — cukes, squash and pumpkins. Even broccoli, which is frost-hardy in the fall, does not go in early. It is much more sensitive now to frost.
What I have found is that soil temperature is very important to success. Yes, you can plant peas or spinach “as soon as the soil can be worked” (as described on the packages), but those seeds won’t germinate and grow if the soil is in the 40s. And the seeds can rot. Seeds have triggers that tell them when to grow. That’s why starting seedlings indoors on heat mats speeds things up. The seeds think it is summer when the soil is 72 degrees. Generally, the soil must be 60 degrees to get a good, quick germination.
So how do you determine the soil temperature? Buy a thermometer designed for it. Generally, these thermometers look like a meat thermometer. The probe is 6 inches or so long. Push 3 inches into the soil and wait for a reading. I hear that digital ones now exist, too.
What can you do to warm up your soil? If you’re in hurry, rake off winter mulch and expose the soil to the sun. Do that now. Then you can cover the soil with a plastic sheet, either clear or black. I’ve found that clear plastic is best. Sun heats the soil directly, and the plastic holds in the heat (but be sure to seal the edges of the sheet with soil to keep the heat in). On a sunny afternoon in the 60s, the temperature under the plastic can exceed 100 degrees.
Another advantage of warming the soil with plastic for a few days is this: you can cook and kill annual weeds. They are sensitive to high temperatures when they first come up. But dandelions or witch grass, which are perennial, have root systems you know and hate. A few hot days under plastic will only make them giggle.
I’m not keen on rototilling. Yes, it will make your garden look very pretty, with not a weed in sight. But for some weeds, each scrap of weed will produce a new plant. Chop up some witch grass and watch it take off! And if you get the top 6 inches of your garden warmed up, and then rototill, all that cold soil below will cool down the rest.
I like to think of all the living things in the soil as my friends. Earthworms, beneficial fungi and bacteria, little arthropods? All of these help to break down organic matter and make it available in a form usable by my plants. And I think of the layers of soil as the floors of an apartment building. Some people like the penthouse, others want a ground-floor room. When you rototill, you jumble up the order of things and put the penthouse in the basement.
So how do I prepare my garden? I create wide, raised beds using only hand tools. I have a five-tined potato fork or hoe that has been in my family for 50 years or more. I use it to loosen the soil and shape the beds. But you can use an ordinary garden fork and a hoe to accomplish the same thing. I pull up soil from the walkways to raise the level of the beds and shape them. I try to disturb the soil as little as possible.
Most of my raised beds are between 24 and 36 inches wide and are 6 to 8 inches above the walkways, which I keep narrow, so as not to waste space. Generally, they have no wooden sides, though I do use planks to contain the soil in a few. I like a wood-sided raised bed for growing carrots, as they need fluffy soil with no rocks in order to get to be 12 inches long, my goal each year. With wood-sided beds, you can build whatever soil you want by mixing in the ingredients.
Before putting your plants in the ground, harden them off. Whether you bought your tomatoes or started them indoors yourself, they can get sunburned or wind-burned if they go outside to a full day’s sun without some preparation. Start with three hours of morning sun, then add some afternoon sun. Watch for signs of stress. After five to seven days of protection from too much wind and sun, they will be ready for planting.
I like to do some cold-season plantings, and I have a cold frame to get a few things growing in April. But I also know that my tomatoes planted in mid-June will catch up with any planted on Memorial Day weekend. Each of us has to figure out what works best.
Henry Homeyer’s blog appears twice a week at gardening-guy.com. Write to him at P.O. Box 364, Cornish Flat, NH 03746. Please include a self-addressed, stamped envelope if you wish a mailed response. Or email [email protected]