I was always more comfortable in art class than math class.
How about you?
For better or worse, we need both subjects in the garden. We need the color wheel and sometimes we need a calculator.
Here are some of the numbers I calculate most often:
- Growing zone. Here’s a post about that in our garden library.
- Average first and last frost dates. Whether you are starting your own seeds or wondering if it’s too early in spring to prune your boxwood or too late in fall to prune a rose, it’s helpful to consult the average first and last dates for freezing temperatures in your area. The internet or a local university or agricultural institution can help you out here. Even better, if you keep a garden journal, you’ll be able to estimate your own average more precisely.
- Date to maturity. This information is usually offered on the back of a seed packet or on a plant label. This is important information if you are growing plants to harvest. For instance, if a fall vegetable needs 90 days to grow from germination to harvest, I do not want those 90 days to extend past the date of my first average freeze. That means there’s a good chance my vegetable plant will be killed by winter weather before I can harvest it. Yes, this math problem requires us to count backwards!
Here are some sample math problems for the garden that are particularly relevant as winter turns to spring and as summer turns to fall:
- When should I start the seeds for my fall garden of cool weather crops like kale or lettuce?
First, check the “days to maturity” information on the seed package.
Then, count backwards that number of days from your average first frost date.
Then add 3 or 4 weeks more to give your seeds time to germinate and grow to a size suitable for transplanting. You’ll have more flexibility with those crops that can tolerate a light freeze (like kale), or if you are covering your plants with fleece or other protective covering.
- When should I start the seeds for my spring and summer garden?
First, consult the average date of last frost for your area or decide when you feel comfortable planting them outdoors (for instance, some plants can tolerate light frost and may be planted out earlier, some, like tomatoes, need to be planted out only after the soil has warmed).
Then, consult the seed packet for information about how many weeks the seeds should be sown before their planting date. The best advice I can give (which I have consistently learned the hard way) is not to start your seeds too early. Strong, healthy seedlings can catch up, but there is little hope for a seedling that has grown leggy while you wait for warmer weather or a seedling that is planted out too soon and killed by a late freeze.
- When should I start the seeds for hardy annuals like snapdragon?
Not all annuals must be completely protected from winter weather. Cool season hardy annuals like snapdragons and sweet peas can be planted in the fall and very early spring. These plants love to get established during cool weather.
In many regions, these flowers can be planted in the fall to winter-over and bloom in spring. Even in colder regions, these flowers should be planted in the earlier spring days, long before the last frost date has arrived.
Consult the growing zone information for the hardy annual you want to grow. For instance, some snapdragons are winter hardy to US zone 4, which means most of us should be planting these cut-flower beauties in fall, not spring.
Here is a handy online calculator for seed starting dates.