Seed-starting questions are already popping up in local gardening discussions on social media and in OSU Extension’s online question answering service “Ask Extension.”
Unless there is space and supplemental lighting to maintain plants indoors for several months, it’s too early to start indoor vegetable seeds in the Klamath Basin. Seedlings grown indoors without sufficient light will stretch out to be tall and leggy, with lots of stem space between leaves. These gangly plants become difficult to transplant when it’s time for them to transition outside.
With some garden seeds in short supply this year, gardeners will want to make the most of the seeds available. One approach to healthy plants includes considering the specific needs of seedlings, which are often significantly different than mature plants of the same type. For instance, seedlings have underdeveloped root systems, and often benefit from mist on the leaves, a practice discouraged on older vegetable plants because it promotes certain diseases. In many vegetables, the ideal temperature for the seed to sprout is different from the ideal temperature for the mature plant’s growth. Exploring some botanical terms associated with seeds and seedlings may be helpful for those seeking to start their own vegetable plants.
The transition from seed to plant. Each plant has ideal conditions for germination, a combination of temperature, soil, moisture, and either darkness or light penetrating the soil. When ideal conditions are unmet, some seeds will germinate, but over a longer time and with less uniformity. Uniform germination is the goal of professional growers: it results in a crop that is easier to care for and is more visually pleasing. Home growers can create conditions conducive to germination with the use of covered seedling chambers to promote humidity, supplemental lights, and heating mats for soil temperature, as budget allows.
The scientific term for “seed leaves.” These first leaves usually fall off the plant, and often look different from the true leaves, which develop later. Seedlings are very fragile while in the cotyledon stage: planting directions often refer to the number of true leaves that should be present before transplanting. Monocot plants like onion and corn have one seed leaf. Most vegetables are dicots, meaning they have two seed leaves.
The leader or “growth tip” of a plant, where a concentration of naturally occurring plant growth hormone is found. In many dicot seedlings, the meristem can be pinched out to produce a bushy plant with multiple leaders, a common practice in professional growing. Monocot plants, and those in the squash and melon family, don’t have the same reaction and should not be pinched.
Seedlings started indoors, or in a greenhouse, develop with consistent temperatures and no wind exposure. Young seedlings transition to outdoor growing more successfully when hardened off. There are a number or ways to accomplish this: using a cold frame, moving plants in and out of doors according to the temperature, or covering plants at night to keep them from getting too cold the first few weeks. The idea is to introduce the young plants to temperature extremes gradually. Sudden exposure to freezing temperatures can shock plants, stunting or even killing them. Stunted plants will take longer to produce food, even when there is little visual evidence of cold exposure.
Not to be confused with hardening off, hardiness refers to the ability of the mature plant to withstand cold and freezing temperatures. When mature, lettuce, spinach, and parsley are considered semi hardy: plants will not be killed by a light frost. Kale, Brussels sprouts, and parsnips are considered very cold hardy, and can even be harvested during freezing weather. Key to understanding hardiness is that is does not apply in the same way to seedlings. A kale seedling that was started indoors, then planted outside in freezing temperatures, will be killed just the same as a tender tomato seedling. Hardening off and hardiness are not the same, but proper hardening off enables an indoor-grown seedling to attain its natural hardiness once it matures.
For those who can’t resist the urge to start planting early, a variety of herbs and loose-leaf lettuces can perform fairly well indoors, especially with supplemental light. Parsley, chives, and cilantro are among the easier of herbs to grow indoors. Parsley, notoriously difficult to germinate from seed, benefits greatly from those ideal germination conditions.
Oregon State Extension provides a table that includes ideal soil temperatures for vegetable seed germination online.
— Nicole Sanchez is horticulture faculty at OSU’s Klamath Basin Research and Extension Center. For more information on this or other gardening topics, contact Sanchez at 541-883-7131 or Nicole.firstname.lastname@example.org.