Seeding Indoors and Outdoors - What and When

A very common outdoor gardening question is what plants can be propagated by seed and when. Take it a step further and ask about seeding plants indoors prior to the growing season - and the what and when gets more interesting and perhaps confusing. All answers boil down to four points of the seasonal planting windows and the plant's preferred growing conditions.

1. Frost Dates - what are the final spring frost dates? Mother's day is often used, don't bet the farm on this date. In '07 the last spring frost was June 8. The first fall frost date - early to mid October, an average at best. We have about 150 frost-free days, give or take.
2. Seasonal windows to plant - from early spring (possibly March, the norm is April) through mid-fall here along the Front Range of Colorado - before, around or after the final spring frost date.
3. Does the plant prefer to grow in cooler daytime temperatures (cool-season crops) or prefer warm days (warm-season crops)? Some gardeners use a soil thermometer to guide their planting schedule. Click HERE for more information.
4. Can the plant be seeded indoors for transplanting outdoors, seeded directly outdoors or planted as a plant?

I'll cover these four points and write about the how to direct seed indoors in a future blog. If you are using cold frames or tunnels for earlier seeding or planting. Move time frames up accordingly. Higher elevation gardeners have a later start date.

Ferris knows about the Seasonal Windows

1) Frost Dates: 

• Most planting charts refer to seeding indoors, outdoors or planting before, near or after the final spring frost. First fall frost dates determine when mid-summer plants are seeded or planted.

2) Seasonal Windows 3) and Cool/Warm Season Plants:

• The first cool season planting period ranges anywhere from March to the middle of May. These include cool weather loving annual vegetables like spinach, peas, lettuce, kale, broccoli, parsley (herb), Brussels sprouts and beets and cool season ornamental annuals like pansy, calendula and sweet peas. This is just a sampling of cool season, check my charts for more plants.
• The warm season window is anywhere from mid-May to the first of July and includes annual vegetables like - tomatoes, peppers, squash and corn, herbs like basil, plus ornamental annuals - petunias, marigolds, sunflowers and cosmos.
• Hardy perennials (long lived), shrubs and trees can be planted during the warm season period and all the way to early fall. Try to avoid planting when temperatures are extremely warm (85+). It can be done, but pay close attention to watering and providing some shade for a few weeks. 
• Exceptions - bare root roses, plus bare root trees and shrubs can be planted almost anytime the soil is workable (not too wet) from March to late April or so. Bare root plants may look like barely alive plants with few, if any roots without a container - just a plastic or burlap wrapping. They are shipped this way - dormant, just follow planting instructions.
• Mid-summer or the fall season is  the third planting window begins - mostly cool season vegetables that mature in sixty days or less and warm season crops that also have a shorter maturity date like summer squash, okra and basil.
• Many perennials, trees and shrubs can be fall planted. The exceptions are conifer and evergreen plants and some perennials that are fall flowering or establish better when spring planted -agastaches are the best example.  

4) Seeding Options. You're in charge, so depending on your time, pocket book and desire to start your own, you don't even have to start seeds indoors. You can choose to direct seed your favorite plants or vegetables outdoors at the right time. OR skip seeding all together and opt for buying transplants - grown by garden centers or your friends who share.

Let's roll up our sleeves and assume you want to start seeds indoors for transplanting your new little plants outside during one of the planting windows. Good for you, seed starting at home is fun and toughens you up whether you succeed, or not. There's no failing grade - you learn from doing.

"What" do you want to start by seed indoors this year? Vegetables, herbs, annuals, and perennials are the big category choices. Within these groups there are ornamental grasses, native plants and fruits. I won't get in to trees, shrubs or roses because most are propagated by cuttings and are much easier to purchase and then plant as potted plants or bare root. 

Bare root plants are available for purchase in garden centers, they start showing up in March or so. Garden centers or mail order offer roses, asparagus, rhubarb, strawberry, raspberry, and blackberry as bare root plants.

Most cane fruit is easier to plant outside as bare root or potted plants. However, there are strawberry seeds which can be started indoors or directly seeded outdoors.
 
Back to "When."
No math stress needed to figure out when to start seed indoors. Simply subtract weeks from the time it takes to plant the seed indoors for it to grow to the correct size before it can go outdoors. It's important to add at least a week of time the plant will take to acclimate from being indoors under lights to living and growing outdoors, this is referred to as "hardening off" the new transplant.

Next, read the seed packet, not all companies use the exact language. Look for the phrase - When to start inside or Propagation. Time frames will be listed in weeks or days.

Let's use the easiest and most popular backyard vegetable as an example - tomatoes (warm season).

Most tomato seed packets will say they need 6-8 weeks before setting outside. Warm season vegetables shouldn't be planted until after the final spring frost, which in the Denver area can be anywhere from Mother's Day or later to early June. 

If using May 15 to plant outside. After 8 weeks growing indoors plus a week of hardening off - direct seed the tomatoes in mid March.



Continuing with "When."
Some seeds can be started in January. This short list includes plants that take longer to grow indoors about 10-12 weeks before they are ready to be transplanted outside. Here's a short list: 

• Cool-season vegetable and herb seeds includes: artichokes, celery, celeriac, onion and leek, parsley.

• Ornamental annuals includes: pennisetum grass, lisianthus (seeding tips), snapdragons, stock, verbena, pansies/viola, geranium, wax begonia, dusty miller, heliotrope, petunia, lobelia, ornamental peppers.

• Perennials include: delphinium, foxglove, dianthus, echinacea (coneflower), eryngium (sea holly), tanacetum (feverfew), rudbeckia (Black-eyed Susan), viola, yarrow, carnation (tender perennial) bee balm (tender perennial), sweet William (biennial, which means it flowers in its second year of growth). 

The best way to know if the plant can be seeded indoors, outdoors or planted as a plant is to read the seed packet or refer to handy charts.

Take advantage of all the great garden classes and seminars along the Front Range or in your area. This is the perfect time to learn the basics of gardening or fine tune what you already know. Click HERE for 2018 resources.

Below is an overview of our planting season and months to seed indoors, outdoors and planting. Look for my planting charts in the next blog.