When to Plant Annuals

3 large pots in a grouping all freshly planted with annuals in a color theme.

These three pots feature a big Kangaroo apple and petunias, salvia, bidens and sweet potato (& more).

When to plant annuals can be tricky business.   I thought I would explain the rule that I use for making this decision.  I call it the 80/50 rule.   Once we have reached 80 degrees for the high and 50 degrees for the low, enough thermal energy has been added to the environment that we are unlikely to get another frost.   Just like it takes a lot of ice to cool down a hot cup of coffee, it takes a big cold front to cool down a warm environment.  The soil and all the plants are warmed up and act as heat syncs.  

Petunia with red streaks leading to center of the flower. Red, yellow and orange tones and many flowers shown.

Petunia ‘Citrus Swirl’ is a Crazytunia new for 2017. It blends well with many other flowers and is profuse blooming.

The 80/50 rule has been reliable for me for several decades here in the Spokane climate.   It would not be so reliable in the Front Range…Colorado warms up only to have a blizzard the next week.  We lack the early warmth, but we are a bit more predictable than the Rockies.  For the Spokane climate, the 80/50 rule has worked well for when to plant annuals.

If I see a forecast for 80/50 later in the week, and the temperatures are OK before that 80/50 day, I pull the ripcord and start installing plants.  We did that on May 2nd this year.   I find the snow on a peak and things like that to be quite unreliable, since that all depends mostly on snow-pack levels that accumulated months prior.  Mother’s Day is a decent rule here; May 20th is our more official frost free date.   But I’m like most gardeners and want to get a jump on it, so I use my 80/50 rule for when to plant annuals.

One of the containers we planted yesterday features a big Kangaroo Apple, as well as Nicotiana, Salvia and more.   Sweet potato vines are impressive after they grow a bit, and many are used in our containers here.  

I don’t apply the 80/50 rule to things like tomato plants or cucumbers.  These are plants that really need sustained 50 degree nights.   You have to wait for sustained warmth for them to thrive.  The annuals will do OK with a few dips around 40, but these tender veggies want it warm.  I hope that helps you decide when to plant annuals.  It has worked for us for some time.  We don’t have a direct line to God for the weather, and we don’t guarantee against frost damage, but this is the best rule we have found for those like me who like to get an early start.

We have containers planted all over the nursery now, so you can get ideas from our baskets or containers as you shop.

purple petunia with a yellow eye or yellow center of the bloom. Many blooms shown

Another Crazytunia, ‘Moonstruck’ has struck us as a particularly beautiful annual.