Colorado spring lawn and garden care: Pruning, planting, aerating, fertilizing and more (2024)

Tuesday, March 19, was the first day of spring. Last week, the Fort Collins area saw snow and rain. This week, temperatures will be mostly in the 60s.

These are all signs that it's time to start spring lawn and garden tasks.

But not all tasks.

Here is the right time and right way to prepare your trees, vegetable garden and lawn this spring:

Why and when you should prune trees, roses and perennials

• If pruning a tree for shape, February and early March are the best times.
• Prune damaged or dead branches or limbs rubbing against each other or those growing upright in the center of the tree anytime of the season, but through February and March are best.
• Prune hardy shrub roses now, but wait until April to prune more tender roses, such as hybrids.
• Prune ornamental grasses back to several inches or to any new green leaves.
• All perennials can be pruned to near the ground in spring.

Read this story for information on how to properly prune trees.

Why knowing Fort Collins' average last frost and freeze is important

The average last frost/freeze dates should be used as a guide, as our spring weather widely fluctuates.

But knowing those dates can test how much you want to gamble on when to plant vegetables and annual flowers and turn on your sprinkler system.

Here are the probabilities of Fort Collins' last spring frost and freeze:

• Frost (32 degrees): 90% until April 23, 50% until May 4 and 10% until May 16, which is why a general rule of thumb is to wait to plant tender plants around Mother's Day (May 12 this year).
• Freeze (28 degrees): 90% until April 5, 50% until April 19 and 10% until May 2.

Here is when to plant vegetables in your garden

• Mid- to late March: Hardier vegetables such as onions, peas, radishes, carrots, lettuce and spinach.
• Early May: Semi-hardy vegetables such as beets, carrots, cauliflower, parsley,potatoesand Swiss chard.
• Mid- to late May: Tender vegetables such as peppers, tomatoes, beans, cucumbers, squash, pumpkin and watermelon.

The truth about when to apply lawn fertilizer and what fertilizer to use

You see and hear a lot of lawn fertilizer commercials this time of year. But not everything in those commercials is applicable to Colorado lawns.

• You don't need to apply fertilizer to your lawn four times a year, as many commercials would have you believe. Two or three applications are sufficient for most Colorado lawns. The best times to fertilize are around Memorial Day, Labor Day and Halloween.
• So-called "weed and feed" fertilizers might appear to save time, but they are more expensive than just fertilizer and unless you have an excessively weedy lawn, the herbicide will be applied to areas that don't require it. This creates waste and can lead to pollution from water runoff from your lawn. Instead, control weeds by pulling or spot spraying.
• Most established Colorado lawns have adequate phosphorus and potassium in the soil without applying additional fertilizer. Look for a slow-release fertilizer that contains mostly nitrogen, the first number in the ratio, much smaller or 0% phosphorous and a low percentage of potassium. If you're unsure of your soil condition, a ratio of 10-0-2 or 4-1-2 is fine.
• Grass doesn't distinguish between nutrients supplied by granular, liquid or organic fertilizers, so use whichever you prefer.

Why aerating is better than power raking for most lawns — and why the earlier you do it, the better

These tasks are best to do sooner rather than later in spring because waiting can cause damage to young grass roots.

• Aeration improves the grass root zone by pulling plugs from the ground, which lessens soil compaction while controlling thatch accumulation. Soil compaction is one factor that contributes to thatch buildup.
• Deep power raking (machine) often removes a substantial portion of the living turf, which is not good. Light power raking (lawn rake) of wet, matted grass can speed spring green-up by letting air move into the root zone and warming the turf.
• You can rent an aerator for about $70 or more, plus a tote trailer, or pay a lawn care company $70 or more depending on the size of your lawn. Usually, the minimum time to rent an aerator is four hours, so you can do multiple lawns to cut individual cost.
• When aerating, make sure your soil is adequately wet, which allows for deeper plugs and better aeration.
• You can allow the plugs to break up naturally, break them up using your lawn mower, or rake them up and compost them.

The truth about leaving grass clippings on your lawn

• Contrary to popular belief, grass clippings do not contribute to thatch accumulation in your lawn.
• Clippings reduce by one-quarter to one-third the amount of nitrogen you need to apply to your lawn because clippings recycle nutrients.
• Mow regularly enough that you only cut one-third of the grass blade length. This is beneficial to the grass blade and keeps clippings short enough to break down faster.
• If weather or another factor prevents mowing at the proper time, raise the height of the mower. Cut the grass again a few days later at the normal mowing height.
• Bluegrass lawns in Colorado should be mowed to a height of 2½ inches in spring, then allowed to grow 3 to 3½ inches as the weather warms. The longer grass length helps retain soil moisture.

When to turn on your sprinkler system and water-saving tips

• The longer you can wait, the better for water conservation but also to lessen the chance of a freeze damaging above-ground parts of your system. This winter, we have received less snow than average but much more precipitation in the form of rain than average, so lawns are in good shape.
• The rule of thumb for watering an established lawn is to do it as deeply and as infrequently as possible. Programming your system to deliver shorter periods of water in two cycles is optimal. This allows water to soak in and results in less water waste.
• Generally, apply 1 to 1.5 inches of water per irrigation. To determine how long this takes, set several shallow containers (such as baking pans) in different areas of the lawn for 30 minutes while irrigating. Measure in inches the depth of water accumulated in the containers for the amount applied in 30 minutes.
• The most efficient time of day to water is 10 p.m. to 6 a.m. Contrary to popular belief, watering at night does not encourage disease development in Colorado.

Step-by-step process to turn on most residential sprinkler systems

• On thebackflow device outside of your home, check the two petco*cks, or pressure release valves, to make sure they are closed.
• Close the valve going from inside your house to the backflow device. This will usually beon the water line below the backflow deviceand the valve going from the backflow device to your outside irrigation line.
• Look for the water line to your irrigation system — usually in the basem*nt, if you have one. Make sure the drain valve on the irrigation lineis tightly closed.
• Very slowly turn on the valve that allows water to run from your main line to the main irrigation line. This pressurizes the system. Do this slowly so you don't damage water lines.
• Turn on the valvegoing from inside your house to the backflow device that you closed in the second step. When you do this, you might hear a pop from atop the backflow device. You know the backflow device is sealed when no water seeps from it.
• Slowly open the valve going from the water line that goes from your backflow device to the outside irrigation linethat you closed in the second step.
• Go to your irrigation control panel, usually in your garage, and manually run each zone to make sure all the heads are working properly.
• Adjust any heads to make sure they are evenly spraying the grass and not hard surfaces.

If a freeze is imminent, here is how to do a quick drain of your system.

Colorado lawn and garden resources

For more Colorado lawnand garden advice, visitextension.colostate.edu/topic-areas/yard-garden/watering-established-lawns-7-199/andextension.colostate.edu/topic-areas/yard-garden/.