When Can I Plant?

Here comes the sun!  With it and the warm day temperatures of spring comes one of the most frequent questions we hear.  “Can I plant this now?”  The answer depends on the plant and particularly, on the nighttime temperatures.  Our early spring days are often beautiful and daytime temperatures may reach well into the 70’s.  It’s the night temperatures that really tell us when it’s safe to plant.  Our last frost date is generally considered to occur around May 20th.  While some years the date arrives earlier, there are occasional years when it occurs as late as June 1.  We’re eager gardeners and antsy to get plants in the ground, but if we aren’t mindful of the night temperatures, we can do more harm than good.

Before I get carried away talking about plants, I should mention the value of hardening off your plants before you plant.   What is hardening off?   It’s a process that acclimates plants prior to transplanting in order to reduce the risk of transplant shock.  The process takes a few days, but it’s worth the investment of time, particularly in early spring or late summer heat.  Day one, place the plants in a shaded area outside and move them indoors or into a garage that night.  Day two, place the plants in partial sun for the day and move into the garage or indoors at night.  Day three, place the plant in a sunny spot for the day and move to a protected outdoor location, like against the house or under a porch, for the night.  Day four, move into the sun for the day and leave them in the exposed location for the night.   Day five, plant.  In late summer, when the temperatures are well over 80°F, I often use the same process, but shortened to 3 days.  This helps prevent sun and wind burn to the young plants.  Hardening off plants increases successful transplanting.

Now back to what we can plant and when we can plant it.

Hands down, the most common plants asked about are tomatoes and peppers.  Tomatoes and peppers, two of the longest season garden vegetables, prefer night temperatures to be above 50°F for about a week before they are planted.  The ground needs to be consistently warm for them to do well.   If we plant too early, and the night temperatures are still cold, plants set less fruit and are often more susceptible to problems like blossom end rot later in the season.

There are helpful tools like Season Starters that can be used to warm the ground earlier than traditional planting would allow.

They should be set up for 7-10 days to warm the soil, before they are planted with your seedlings.  Once planted, the plant protectors act as insulators against cold temperatures, much like a mini greenhouse.  Generally, Season Starters can give you a jump start by several weeks.  Set them up about April 15 and you can plant inside them a week later.   

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We hope this Frost Hardiness list will help gardeners know when it is safe to set out their plants. The actual dates vary, of course, with each area, but the principle is the same. Perennials that are not hardy in Colorado are listed as annuals. The hardiness of perennials is based on coming out of a protected climate.

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Very Hardy Plants–Plant Out up to 7 weeks before last frost.
(April 1 in Denver, April 10 in Golden & Parker)

PansyAnnuals
Alyssum, Anchusa, Centaurea, Dracaena, Dusty Miller, Larkspur, Nigella, Pansy, Snapdragon, Sweet Pea

Perennial Starts
Achillea, Aegopodium, Ajuga, Aurinia, Arabis, Armeria, Aubretia, Basket of Gold, Bishop’s Weed, Carnation, Creeping Phlox, Gayfeather, Hardy Hibiscus, Lavender Cotton, Liatris, Lobelia, Primrose, Primula, Rock Cress, Purple Rock Cress, Red Hot Poker, Santolina, Sedum, Thyme, Torch Lily, Tritoma, Viola, Yarrow

Vegetable Plants
Asparagus, Chives, Fennel, Garlic, Onions, Peas, Potato, Radish, Strawberry

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Hardy Plants–Plant up to 5 weeks before last frost.
(April 20 in Denver, April 30 in Golden & Parker)

Annuals
African Daisy, Arctotis, Baby Blue Eyes, Calendula, Carnation, Dianthus, Diascia, Flowering Kale, Lobelia, Osteospermum, Phlox, Twinspur, Vinca Vine

Perennial Starts
Alstromeria, Anemone, Baby’ Breath, Bachelor Buttons, Bellis, Campanula, Candytuft, Centaurea, Cerastium, Columbine, Coral Bells, Coreopsis, Daylily, Dianthus, Digitalis, Doronicum, English Daisy, Erysimum, Festuca, Feverfew, Flax, Forget-Me-Not, Foxglove, Galium, Garden Mums, Gloriosa Daisy, Gypsophila, Helianthemum, Hemerocallis, Heuchera, Hollyhocks, Hosta, Iberis, Lavender, Lenten Rose, Lupine, Lunaria, Lysimachia, Maltese Cross, Matricaria, Mexican Feather Grass, Missouri Primrose, Money Plant, Myosotis, Oenothera, Painted Daisy, Penstemon, Tall Phlox, Pincushion Flower, Poppy, Pyrethrum, Roses, Rudbeckia, Scabiosa, Shasta Daisy, Snow-in Summer, Statice, Sweet William, Sweet Woodruff, Veronica, Violet

Vegetable Plants
Broccoli, Brussels Sprouts, Cabbage, Cauliflower, Kohlrabi, Lettuce, Pak Choi, Perennial Herbs, Radicchio, Rhubarb, Spinach

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Half-Hardy Plants–Plant out up to 3 weeks before last
frost date.
(May 1 in Denver, May 10 in Golden & Parker)

Annuals
Anagallis, Angelonia, Angel’s Trumpets, Bacopa, Bells of Ireland, Blue Lace Flower, Calibrachoa, California Poppy, Campanula, Clover, Coreopsis, Cosmos, Creeping Zinnia, Datura, Dichondra, Didiscus, Fountain Grass, Gaillardia, Gazania, Gerbera, Gloriosa Daisy, Gomphrena, Lotus Vine, Ornamental Grasses, Petunia, Pennisetum, Phlox, Purple Bell Vine, Regal Geranium, Ruby Grass, Rudbeckia, Sanvitalia, Scarlet Pimpernel, Stocks, Strawflowers, Steirodiscus, Sutera, Sweet Peas, Sweet Sultan, Transvaal Daisy, Trifolium, Verbena, Xerianthemum

Perennial Starts
Artemesia, Hardy Asters, Astilbe, Balloon Flower, Bee Balm, Bleeding Heart, Delphinium, Echinacea, Euphorbia, Felicia Daisy, Geum, Gladiolus, Hibiscus, Hypericum, Monarda, Peony, Platycodon, Purple Coneflower, Roses, Salvia, Sagina, Saxifraga, Verbena

Vegetable Plants
Artichoke, Celery, Leek

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Tender Plants–Plant outside after almost all danger of
frost has passed.
(May 20 in Denver, May 30 in Golden & Parker)

Annuals
Abutilon, Achimenes, African Daisy, Ageratum, Argyranthemum, Alternanthera, Alternaria,amaranthus, Asparagus Fern, Asters, Axilflower, Balsam, Banana, Begonia, Bidens, Black Eyed Susan, Bloodleaf, Blue Throatwort, Bougainvillea, Bower Vine, Brachycome, Browallia, Brunfelsia, Caladium, Calla Lily, Calliopsis, Canna, Cardinal Flower, Catharanthus, Celosia, Chrysanthemum, Chrysocephalum, Cigar Plant, Cleome, Coleus, Copperleaf, Crassula, Crossandra, Cuphea, Dahlberg Daisy, Dahlia, Dallas Fern, Dipladenia, Elephant Ears, Evolvulus, Fanflower, Fiber Optic Grass, Flowering Maple, Flowering Tobacco, Fountain Grass, Four O’ Clock, Fuchsia, Geranium, Gloriosa Lily, Firebush, Guara, Hamelia, Heliotrope, Hibiscus, Impatiens, Iresene, Jasmine, Lantana, Livingstone Daisy, Lisianthus, Lithospermum, Marguerite Daisy, Marigold, Mecardonia, Melampodium, Millet, Mimulus, Monkey Flower, Moon Vine, Morning Glory, Napa Valley Fern, Nasturtium, Nemesia, Nicotiana, Nierembergia, Nolana, Oleander, Oxalis, Painted Tongue, Pampas Grass, Pentas, Perilla, Periwinkle, Plectranthus, Polka Dot Plant, Polygonum, Portulaca, Salpiglossis, Salvia, Sanvitalia, Scarlet Runner Bean, Scaevola, Scutellaria, Schizanthus, Skullcap, Statice, Stoneseed, Streptocarpella, Sunflower, Swan River Daisy, Sweet Potato Vine, Thunbergia, Tithonia, Torenia, Trachelium, Trailing Portulaca, Tropical Hibiscus, Tropical Water Plants, Zinnia

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Vegetable Plants
Annual Herbs, Cantaloupe, Corn, Cucumber, Eggplant, Okra, Peanut, Bell & Chile Peppers, Pumpkin, Squash, Sweet Potato, Tomato, Watermelon

FROST HARDY PERENNIALS, ANNUALS AND VEGETABLES
To obtain maximum frost hardiness, HARDEN PLANTS OFF gradually by exposing them to sun, wind, and cold, but above freezing temperatures for a few days.

Very Hardy (After April 1st)

Flowers: Achilles (Yarrow)
Aegopodium Bellis Iberis (Candytuft) Roses,Bare Root
Ajuga Carnation, Grenadin Iris Santolina
Alyssum Cerastium (Snow in Summer) Liatris Sedum
Arabis (Rock Cress) Columbine Lobelia, Cardinalis Thyme
Armeria Creeping Phlox Myosotis Tritoma (Red Hot Poker)
Aubrietia Euphorbia Penstemon Viola
Hibiscus (Purple) Euonymus Primula (Primrose)

Vegetables: Asparagus Chives Rhubarb Strawberries

Hardy (After April 15th)

Flowers: Alstromeria Helianthemum Scabiosa
Anemone Hemerocallis Shasta Daisy
Campanula Hollyhocks Statice
Centaurea (Bachelor’s Button) Hosta Sweet William
Coral Bells Lavender Veronica
Coreopsis Lupines Violet
Daylily Lunaria (Money Plant)
Delphinium Lysimachia
Dianthus Lythrum
Doronicus Maltese Cross
Festuca Myosotis (Forget-Me-Not)
Flax Oenothera
Foxglove Phlox, Tall
Galium Poppy
Garden Mums Pyrethrum (Painted Daisy)
Gypsophila (Baby’s Breath) Rudbeckia (Gloriosa Daisy)

These dates are approximate for the Denver area. Safe dates vary from year to year, suburb to suburb, and even from one location in the garden to another. Covering plants on unusually cold nights will help protect them. On extremely cold nights it may be necessary to dig plants up and bring them inside.

Seed Starting Basics

Have you ever gone to the grocery store and said oh my 4 dollars for 4 sprigs of basil. Well there is an easy way to get what you want and help you save a bit of cash, as well. Not only will starting your vegetables, herbs, and flowers from seed help the pocket book, it is a wonderful thing for the whole family to watch a plant grow from a tiny seed, and there is nothing more rewarding than harvesting a crop that you grew.OLYMPUS DIGITAL CAMERA

The first thing to do is determine where you plan to plant your garden outdoors. Most vegetables require full day sun to mature properly. There are only a few that will grow in partial sun, mostly leafy greens. Knowing your available light will determine what you can successfully grow. It’s also a good idea to have a basic soil test done to determine the big three nutrients available in your soil – Nitrogen, Phosphorus and Potassium. The information will let you know what amendments may be needed.

Read the seed packet. There should be a description of plant characteristics, giving you an idea of what to expect. Look for information about the preferred season to grow, seed sowing depth, days to germination, and days from transplant until harvest. There should also be information about preferred light and whether or not the seed will do best if started indoors or directly sown into the outdoor garden bed. Often there is information about the disease resistance of the variety, too. In the case of tomatoes, there should be a notation of the plant being determinate or indeterminate. Some seed companies provide additional information inside the packet. If you prefer to use organic seed, look for the USDA organic symbol on the front of the packet. You won’t find GMO seeds at Echter’s. In fact, GMO is primarily used on commercial farms and is rarely seen in the garden center or home garden.

Why is the information on the packet important? All of that information allows you to select the right varieties to grow in your climate and those that suite your both your needs and taste buds.

Is the plant warm season or cool season?
This will help you decide when to plant said crop for instance things like spinach, kale, chard, Brussels sprouts, are all cool season crops. Meaning you can start those 4-6 weeks before the average last frost. Whereas things like peppers, tomatoes, zucchini, need to be started after the last frost. I know it can be confusing but on most seed packets you will have that information of cool season or warm season right on the front.

What is days to emerge?
This is how many days it will take that seed to as we say crack or germinate. It is when you will see the first sign of life the first little showing of green.

How many days until harvest?
This means how many days it will take from the time you plant in the ground or container, till you will be able to harvest said crop, or see blooms on flowers.
Should I start my seeds indoors our outside?
Most seed packets will recommend whether to start inside or outside. For instance it is a good idea to start your tomatoes and peppers inside since Colorado has such a short growing season. Whereas things like corn, leafy salad greens and root crops like carrots prefer to be directly sown into the ground.

Now that you can identify what and when to plant there is no stopping you! You will have a few other needs to get started. You’ll need seed trays and seed starting mix or Jiffy pots. It’s also helpful to have some plant labels so you can note the date the seed was sown and the variety. A heat mat is helpful, particularly if your home temperature is on the cools side. It will heat the soil evenly, providing optimal conditions for seed germination. Humidity domes can help keep the necessary moisture around the seed to aid in germination. If the light on your windowsill is inadequate, try adding indoor grow lights. Most are energy efficient and you’ll use them for years to come. If you are starting indoors it will be important to have additional pots on hand, usually 3”-4” diameter. Once seedlings have established, they will need to be potted up until it is time to transplant outside.

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It’s a good idea to keep the empty seed packets for a couple of reasons. The first is that it can be a few months before your plants reach maturity. In that time, it’s easy to forget details that may be handy to know as harvest time approaches. The second is that you may find out you love that variety and having the seed packet will help you remember what to buy the following season.

It is important to remember that gardening involves some trial and error, and there is no fool proof method. Mother Nature has her own ideas sometimes. It never hurts to try new things. If you are successful you will not only reap the benefits of tasty veggies, aromatic herbs, and beautiful flowers, but the confidence that, yes, you can grow something from a seed.