Yes you can cut it level. Here is an excellent article I found on the forum regarding trimming plants.
Published in Tropical Fish Hobbyist, November 2005
Translated by Tomoko Schum
In last month's issue, I explained the method for planting aquatic plants. Aquatic plants grow well when the substrate is set up and the filter, lighting, and CO2 are working together to make environmental conditions in the aquarium ideal for plant growth.
Left unchecked, however, aquatic plants grow too tall and the layout becomes unattractive. Since stem plants and other sun-loving aquatic plants in particular grow rapidly, trimming down to size is important. With trimming, stem plants grow multiple terminal buds, and their stems and leaves grow densely. Repeated trimming shapes the beautiful thicket of stem plants.
Trimming of aquatic plants is best performed with specialized scissors. Scissors made for trimming aquatic plants are characterized by their sharp edges and long handles. The sharp edges cut without squashing the cells near the cut surface, thus lessening damage to the aquatic plants during trimming, and the long handles enable you to reach into the intricate part of the layout. Trimming scissors are very handy for trimming stem plants into well-formed bushes.
Trimming is also essential for maintaining Glossostigma, Riccia, and hair grass over a long period of time. These aquatic plants are relatively short, and the cutting height is very low near the substrate. Therefore it is difficult to cut a large area horizontally with straight-bladed scissors. For trimming this type of plant, I use scissors with curved blades. I use scissors in different sizes and shapes depending on the aquatic plant types and the location of the cuts. If you are new at this, I recommend trying basic style trimming scissors first. You can add curved blade trimming scissors to your collection if you feel the need. This makes a difference in the ease of operation and the finished condition.
If you have your tools ready, let's start trimming aquarium plants! The first trimming of stem plants is done when their stems have grown upward to some extent. Stem plants grow relatively fast. If left unchecked, their terminal buds reach the water surface in short order, and the plants start overhanging along the water surface. I recommend that you trim them sooner since the condition of the lower part of their stems becomes poor once they reach this point. Over the bottom part of the stem plants where light does not reach very well, they eventually lose their leaves, put out roots, and become unsightly. In the Nature Aquarium, Cryptocoryne and other aquatic plants are planted, or driftwood is placed in the mid-ground, to hide this part.
Although it depends on the layout, you should generally trim for the first time along the outline of a compositional material such as driftwood, which can serve as a useful guide for trimming. Normally, multiple shoots develop from a stem in a week or two after trimming. Taking advantage of this nature of stem plants, the second and subsequent trimmings are done at a location that is a little higher than the previous trim position. This encourages the tip of a stem to branch out and the stem and its leaves to grow densely.
When you trim stem plants, it is also important to sculpt the overall shape of the bush. Envisioning the way they grow, you must trim the bush so that the stem plants will grow into a beautiful bush in two to three weeks. One or two shoots start to protrude before all the stems grow out; if this happens, this type of shoot must be cut off immediately.
Various aquatic plants other than stem plants are used in an actual layout. These aquatic plants should be trimmed at the same time to keep their growth in balance. First of all, Glossostigma and Riccia in the foreground need to be thinned down as much as possible, since they grow into a thick mat if not trimmed, and they tend to dominate the layout space. As I explained earlier, I thin this section down using curved trimming scissors.
It is also important to trim willow moss that is grown attached to driftwood; if willow moss is allowed to grow unrestricted, it covers the driftwood completely, which makes the driftwood appear too bulky and destroys the overall balance of the layout. You can tear the moss off by hand to a certain extent, and then cut away any protruding part with scissors. If a fern such as Microsorium sp. is grown on driftwood, large leaves should be cut off frequently. By doing so, the size of its leaves gradually becomes smaller and the fern looks more attractive. Any leaves that are starting to touch the glass surface should be cut off since they can create a crowded, claustrophobic feeling.
Among others, the family of hairgrass needs periodic trimming. If hair grass is trimmed down to about 1 cm from the root, new leaves develop quickly and the plant appears attractive again. The leaves of hair grass also become gradually smaller with repeated trimming. Eleocharis vivipara, a family of hair grass, forms plantlets at the tips of its leaves. These plantlets should be removed frequently to maintain a clean look, since the layout looks untidy when too many plantlets appear.
The maintenance of aquatic plants after trimming is important as well. Although stem plants are relatively tolerant of trimming, the lower stems near the root become old and new shoots do not develop easily with repeated trimming. When this happens, I add a fertilizer containing some plant hormone to encourage the development of new shoots. If the stems become overly aged and the base of the plant lifts up from the substrate, I pull out the entire stem plant, trim off the older bottom section, and replant the top younger sections of the stems. You can enjoy stem plants over a long period of time through trimming and rejuvenating in this manner.
For tall-growing stem plants, mid-ground ferns, and low-growing ground cover and mosses, proper trimming and maintenance is essential to the long-term success of a beautiful Nature Aquarium layout.