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When is the Best Time to Plant?
By Rita Pelzar, Organic Gardening Magazine
Too Cold or Too Wet?
If you've read a spinach-seed packet, then you've probably seen the advice "sow as soon as the soil can be worked in spring." But what exactly does this mean? We called on a team of horticulturists and soil scientists to help us identify clues that indicate if soil is ready for seeds and transplants. After a little digging, our experts revealed that learning your soil's temperature and moisture content is the key to knowing when to sow and grow.
Each vegetable crop has an ideal temperature range that promotes optimal growth. Cool-season crops, such as kale and peas, grow faster and resist disease better at lower soil and air temperatures than warm-season crops, such as tomatoes and eggplants. If the soil is too cold at planting time, "germination and early growth is slowed, which leaves the new seedling exposed and vulnerable to soil microbial and fungal attacks," explains Tony Bratsch, an extension vegetable specialist with the Virginia Cooperative Extension Service in Blacksburg, Virginia.
Getting your soil's moisture content right is a bit of a balancing act: If there's too much moisture, your seeds will rot; too little, and they won't germinate. Wet soils can contribute to disease problems, "and even 'drown' the seed by limiting oxygen uptake critical for early seedling growth," adds Bratsch. Working in wet soil can also damage its structure, resulting in hard clods that take years to break back down.
Signs of Spring
Noting when certain native trees and hardy annual weeds begin to grow or bloom in your area enables you to fine-tune your spring planting dates. For example, early peas can be planted when chickweed (Stellaria media) or pussy willow (Salix discolor) blooms, provided the soil is not too wet. By observing early signs of spring, you may find that nature's clues are more reliable than a calendar.
Get a Head Start
Get an extra-early head start on your vegetable garden by trying one of these techniques:
Use raised beds. Plant early vegetables in raised beds, which tend to drain better and warm up earlier than in-ground beds.
Warm the soil. Cover some of your garden beds with sheets of black plastic for a couple of weeks before you want to plant. Remove the plastic before planting, or plant seedlings through holes cut into it.
Build plastic tunnels. Protect early plantings from cold or overly wet weather by growing them under clear plastic. Linda Brewer, a horticulture research assistant and Oregon State University, uses rebar and PVC pipe to support the plastic over her early vegetable beds. "This gives me a chance to exclude rain and increase the rate at which the soil warms," she says.
Take advantage of micro-climates in your yard. A protected garden bed in front of a south-facing wall may warm up a few weeks earlier than exposed areas.
5 Steps to Seed Sowing Success
Step 1: Know your average last-frost date. This date, which is specific to your location, is the average date of the last spring frost as observed over several years. Call your county extension service (it's in the blue pages of your phone book) for the date.
Step 2: Determine your soil's temperature. A soil thermometer is the most accurate way to take your soil's temperature. Simply stick the probe into the soil and wait to see consistent readings for a few days. Plant when the soil reaches your crop's ideal temperature. A soil thermometer with an 8-inch probe costs about $9.
Step 3: Test soil moisture. Dig down 4 to 6 inches, grab a handful of soil, and squeeze it into a ball. Then try to crumble it between your fingers. If it won't crumble and feels a bit like brownie batter, it's too wet. Wait a few days and try again. If it crumbles easily, it's ready for planting. If the soil slides through your fingers, it's too dry. Soak the soil and let it drain. Plant once it passes the squeeze test.
Step 4: Know your crops. Figure out what soil temperatures your favorite vegetables prefer and what weather they can tolerate. Nancy Bubel's guide, The New Seed-Starters Handbook, lists the ideal temperature ranges of most vegetables. Use your last-frost date to establish planting dates. Just be sure than the soil is warm and dry enough before planting.
Step 5: Add organic matter. Regularly incorporating organic matter (compost, cover crops, etc.) into soil improves its tilth - physical condition and workability. A soil with good tilth drains well and is easy to cultivate, conducive to seed germination and root growth, and resistant to crusting. |
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