Now that you have your seeds and you’ve decided which seeds to start indoors and which to direct sow, the question becomes, when do you plant?
Determining when to start seeds for transplants
Starting your seeds indoors at the right time will give you nice, healthy, transplant-size plants at the ideal planting time in the spring. The correct timing depends upon where you live (what your average last frost date is) and the type of vegetables you grow.
Cool season crops like broccoli, cabbage, and cauliflower are tolerant of colder temperatures and transplants can be placed out in the garden earlier than warm season crops.
In general, cool season crops for transplanting should be grown indoors for about 4 to 6 weeks, but they can be planted outdoors 2 or 3 weeks before the last frost date. For some, these crops can be started pretty soon!
Warm season crops should be grown indoors for about 6-8 weeks but they should not be transplanted into the garden until a week or two after the last frost date. It doesn’t do any good to plant warm season crops like tomatoes, peppers, and eggplant early because, if the soil and/or air temperature is not optimal, the plants will just sit and not grow much until it gets warmer. These plants need warm temperatures to spur growth.
Here is a link to calculate (by zip code) your average date of last 32°F temperature (50% column on the chart).
Johnny’s Selected Seeds has developed a chart that will give you a date range for starting your seeds indoors and also when it is best to transplant your seedlings outdoors. All you need to do is input your spring frost-free date. You might want to use a more conservative date for this – maybe the 20% column rather than the 50% (average date) column.
When to sow seeds directly in the garden
The timing for direct seeding into the garden is really more dependent on the spring weather conditions and the temperature of the soil. In general, it is safe to sow seeds directly in the garden after the last frost date but most vegetable seeds have specific soil temperature requirements for germination. It’s not the air temperature but the soil temperature that is critical in seed germination. Seeds begin growing when the soil reaches the optimal temperature for germination.
Seeds can rot in the ground before they germinate if planted in soil that is too cold – a waste of time and money!
Peas can be planted early since they are more cold hardy plants. Pea seeds can germinate in soils as cool as 40°F; whereas cucumbers germinate best when the soil temperature is 70°F and will not germinate at all if the soil temperature is below 50°F.
As you can see, it can be really helpful to have a soil thermometer!
Your seed packets will often provide information on the optimal soil temps for germination and this is the best guideline to follow. Many seed websites, like Johnny’s Selected Seeds, provide detailed growing information including when to direct seed each variety.
A word of caution!
Never work in the soil when it is wet – even if the soil temperature is perfect for planting. Digging or tilling in wet soil (or very dry soil) can destroy its structure by compressing the soil particles tightly together so that the pore spaces that hold air and water are lost. This hinders aeration and drainage and can quickly turn good soil into something almost as hard and crusty as concrete.
It is very important to make sure your soil is dry enough before you get in there and tromp around in the garden. You can test this by taking a handful of soil and squeezing it into a ball. If the ball breaks apart when you tap it, the soil is dry enough to be worked.
Using Phenology to determine planting time
Rather than going by a certain calendar date, some gardeners use phenology to determine the optimal time for various gardening chores, such as planting, pruning, weed control, etc. Phenology is the study of the timing of certain events in nature (for instance, the swelling of buds or the appearance of flowers) in relation to weather and climate.
For generations, many farmers and gardeners have relied on these observations of nature rather than the calendar. Plants and animals don’t know when the first day of spring is or what the average date of last frost is but they do respond to changes in local temperature and precipitation and their responses can give us a pretty good idea of how spring is progressing (or not) in any particular year.
“Indicator plants” are commonly used as a guide for planting and other spring chores.
Lilacs have proven to be a good indicator plant but one of Andre’s favorites is forsythia.
He says …
- When the forsythia are in bloom, it’s time to direct sow cool-season crops in the vegetable garden. These include: spinach, lettuce, peas, carrots, chard, beets, and radishes.
- When the forsythia are in full bloom, it is time to prune your hybrid tea roses, floribunda roses, and grandiflora roses.
- Before the forsythia petals drop, apply a pre-emergent herbicide to control crabgrass in your lawn.
- When the forsythia petals begin to drop, cut your Buddleia (butterfly bushes) back to about 12″-18″ from the ground. Use this same timing for cutting back your Caryopteris and Vitex.
- When the forsythia have finished blooming, you can safely plant potatoes.
Here are some others:
- When daffodils bloom, plant spinach, beets, onions, and kale
- When apple blossoms drop their petals or the lilacs are in full bloom, plant bush beans, pole beans, cucumbers, squash, and corn
- When peonies flower, transplant tomatoes, peppers, eggplant, and melons
Well, there you have it; a few good tips on when to do some planting!